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Cardiolipin (CL) is a unique, four-chain phospholipid synthesized in the inner mitochondrial membrane (IMM). The acyl chain composition of CL is regulated through a remodeling pathway, whose loss causes mitochondrial dysfunction in Barth syndrome (BTHS). Yeast has been used extensively as a model system to characterize CL metabolism, but mutants lacking its two remodeling enzymes, Cld1p and Taz1p, exhibit mild structural and respiratory phenotypes compared to mammalian cells. Here, we show an essential role for CL remodeling in the structure and function of the IMM in yeast grown under reduced oxygenation. Microaerobic fermentation, which mimics natural yeast environments, caused the accumulation of saturated fatty acids and, under these conditions, remodeling mutants showed a loss of IMM ultrastructure. We extended this observation to HEK293 cells, where phospholipase A2 inhibition by Bromoenol lactone resulted in respiratory dysfunction and cristae loss upon mild treatment with exogenous saturated fatty acids. In microaerobic yeast, remodeling mutants accumulated unremodeled, saturated CL, but also displayed reduced total CL levels, highlighting the interplay between saturation and CL biosynthesis and/or breakdown. We identified the mitochondrial phospholipase A1 Ddl1p as a regulator of CL levels, and those of its precursors phosphatidylglycerol and phosphatidic acid, under these conditions. Loss of Ddl1p partially rescued IMM structure in cells unable to initiate CL remodeling and had differing lipidomic effects depending on oxygenation. These results introduce a revised yeast model for investigating CL remodeling and suggest that its structural functions are dependent on the overall lipid environment in the mitochondrion.

Barth syndrome is a rare genetic disease caused by abnormal cardiolipin metabolism, characterized by high mortality within 5 years of diagnosis due to heart failure and/or infectious complications. This article describes a clinical case of an adult patient with Barth syndrome. The peculiarities of the course of the disease are described, including the transformation of the hypertrophic type of cardiomyopathy into the hypokinetic type as the patient grew older. This article demonstrates the difficulty in selecting the optimal treatment of a patient with Barth syndrome in real clinical practice, in the absence of clearly prescribed recommendations and pathogenetic therapy.

Cardiomyopathy is the predominant defect in Barth syndrome (BTHS) and is caused by a mutation of the X-linked Tafazzin (TAZ) gene, which encodes an enzyme responsible for remodeling mitochondrial cardiolipin. Despite the known importance of mitochondrial dysfunction in BTHS, how specific TAZ mutations cause diverse BTHS heart phenotypes remains poorly understood. We generated a patient-tailored CRISPR/Cas9 knock-in mouse allele (TazPM) that phenocopies BTHS clinical traits. As TazPM males express a stable mutant protein, we assessed cardiac metabolic dysfunction and mitochondrial changes and identified temporally altered cardioprotective signaling effectors. Specifically, juvenile TazPM males exhibit mild left ventricular dilation in systole but have unaltered fatty acid/amino acid metabolism and normal adenosine triphosphate (ATP). This occurs in concert with a hyperactive p53 pathway, elevation of cardioprotective antioxidant pathways, and induced autophagy-mediated early senescence in juvenile TazPM hearts. However, adult TazPM males exhibit chronic heart failure with reduced growth and ejection fraction, cardiac fibrosis, reduced ATP, and suppressed fatty acid/amino acid metabolism. This biphasic changeover from a mild-to-severe heart phenotype coincides with p53 suppression, downregulation of cardioprotective antioxidant pathways, and the onset of terminal senescence in adult TazPM hearts. Herein, we report a BTHS genotype/phenotype correlation and reveal that absent Taz acyltransferase function is sufficient to drive progressive cardiomyopathy. [ABSTRACT FROM AUTHOR]

Barth syndrome (BTHS) is a rare X-linked recessive genetic disorder characterized by a broad spectrum of clinical features including cardiomyopathy, skeletal myopathy, neutropenia, growth delay, and 3-methylglutaconic aciduria. This disease is caused by loss-of-function mutations in the TAFAZZIN gene located on chromosome Xq28, resulting in cardiolipin deficiency. Most patients are diagnosed in childhood, and the mortality rate is highest in the early years. We report a case of acute, life-threatening metabolic decompensation occurring one day after birth. A novel TAFAZZIN splice site mutation was identified in the patient, marking the first reported case of such a mutation in BTHS identified in China. The report aims to expand our understanding of the spectrum of TAFAZZIN mutations in BTHS.

Background Barth syndrome is a rare, life-threatening X-linked recessive mitochondrial disorder of lipid metabolism primarily affecting males. Previous research suggests that bezafibrate may ameliorate cellular lipid abnormalities and reduce cardiac dysfunction in an animal model. Objectives Estimate the effect of bezafibrate on clinical, biochemical, and quality-of-life outcomes. Investigate whether within-participant clinical changes parallel in vitro changes in cardiolipin ratio/profile and mitochondrial morphology when each participant’s cells are cultured with bezafibrate. Investigate as for objective 2, culturing each participant’s cells with resveratrol. Describe the most feasible methods and standardised outcome measures to optimise the conduct of future trials and evaluations in Barth syndrome. Describe features of the research infrastructure which optimised recruitment, retention and communication with families and people with Barth syndrome. Describe the perceptions of participants and their families about the research and any important potential barriers to participation. Design Randomised, placebo-controlled, crossover trial of bezafibrate versus placebo. Setting NHS hospital providing UK-wide Barth Syndrome Service. Participants Males aged ≥ 6 years with a confirmed diagnosis of Barth syndrome with stable cardiac status, able to swallow tablets of bezafibrate/placebo. Exclusions were: hypersensitivity or allergy to bezafibrate or any component of bezafibrate; hepatic, liver or renal dysfunction; gallbladder disease; or recent deterioration in general health. Interventions Fifteen weeks of bezafibrate in one period and placebo in a second period, or vice versa (randomly allocated), with at least a 1-month washout between periods. Main outcome measures The primary outcome was peak VO2; secondary outcomes were cardiac function rest and exercise echocardiography and magnetic resonance imaging, cardiolipin ratio, quality of life, dynamic skeletal muscle P-magnetic resonance spectroscopy, mitochondrial studies and neutrophil counts, and adverse events. Outcomes were measured at baseline and the end of each period. Results Eleven males were studied; all attended all three assessments. There was no difference in peak VO2 between periods (0.66 ml/kg/min lower with bezafibrate than placebo, 95% confidence interval 2.34 to 1.03; p = 0.43). There was a trend towards a higher left ventricular ejection fraction with bezafibrate when measured by echocardiography but not magnetic resonance imaging, and better echocardiography-derived rest longitudinal and circumferential strain with bezafibrate. There was no difference in quality of life or cardiolipin ratio between periods. Skeletal muscle 31P magnetic resonance spectroscopy was performed cross-sectionally and showed a trend to higher Tau and lower Qmax indices in the bazafibrate group. Two participants had serious, expected adverse reactions when taking bezafibrate; otherwise, bezafibrate was well tolerated. Limitations The sample size was very small; the bezafibrate dose may have been too low or 15 weeks too short to observe an effect; measurements of mitochondrial content and membrane potential were highly variable; P-magnetic resonance spectroscopy was available only at the final assessment. Conclusions This study did not show significant improvement in the primary and secondary outcomes with bezafibrate treatment. Future work Elamipretide, studied in a small crossover trial in the USA, is another potential intervention which may be worth evaluating in an international study. Trial registration This trial is registered as ISRCTN58006579. Funding This award was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation (EME) programme (NIHR award ref: 12/205/56) and is published in full in Efficacy and Mechanism Evaluation; Vol. 11, No. 13. See the NIHR Funding and Awards website for further award information. Plain language summary Barth syndrome is a rare genetic syndrome with mutations in the tafazzin gene causing long-term effects in several organ systems, leading to significant lifelong comorbidities and a reduced quality of life. Barth syndrome shows an X-linked inheritance, hence it is almost exclusively present in males. Tafazzin gene mutations impair overall cell energy metabolism, and affected individuals show compromise of the immune system with a high risk for life-threatening infections, as well as cardiac dysfunction and cardiomyopathy, muscle and general fatigue, and generally reduced mobility also leading to psychological challenges and dysfunction. Currently, specific medical therapies are limited to symptomatic treatment, and drug therapies targeting the causative mitochondrial energy disturbance are urgently needed. This randomised controlled trial explored the use of oral bezafibrate, a licensed drug that can improve cell energy metabolism. Eleven male patients received either bezafibrate or a placebo for 4 months. Exercise capacity by cardiopulmonary exercise testing on a cycle ergometer, as the primary outcome measurement, as well as cardiac function by echocardiography and magnetic resonance imaging, and cellular anatomy and function by in vitro assays and microscopy, were measured before and after this 4-month period. Bezafibrate did not significantly improve exercise capacity, cardiac function or the cellular metabolism, although several cardiac function parameters showed slight improvements with bezafibrate treatment. No significant adverse effects were recorded. The limitations of the trial were its low participant number and the relatively short duration of the drug treatment phase. The trial did prove that complex randomised controlled drug trials are feasible in people with rare diseases. Adherence was good, with parents reporting few difficulties with pill swallowing. The qualitative interviews also found that the study was acceptable to participants and the burden of participating not too onerous. We hope the research can provide a template for future studies. Scientific summary Introduction Barth syndrome is a very rare, life-threatening, X-linked recessive genetic disease almost exclusively affecting young males, caused by abnormal lipids in mitochondria. The tafazzin gene (TAZ) encodes tafazzin, a phospholipid acyltransferase. Tafazzin transfers unsaturated fatty acids with acyl chains from phospholipids to monolysocardiolipin (MLCL) and regulates remodelling and maturation of cardiolipin, a phospholipid located exclusively in the inner mitochondrial membrane. Mature tetralinoleoyl-cardiolipin (L4-CL) is essential in the mitochondrial membrane for maintaining mitochondrial membrane potential, structural integrity of electron transport chain complexes and mitochondrial cristae architecture. Cardiolipin is a major constituent of inner mitochondrial membranes, and the major effects of the aberrant gene are on muscular tissues. Cardiac and skeletal manifestations of Barth syndrome are thought to result from impaired formation of respiratory chain super-complexes. TAZ mutations decrease L4-CL and increase intermediate species of MLCL, resulting in a marked increase in the MLCL : L4-CL ratio, which provides a highly sensitive and specific biochemical test for Barth syndrome. Barth syndrome is characterised by many gene mutations and profound phenotypic variability between affected patients within families and those in different families. The disease carries many risks and problems for its sufferers, as well as major healthcare costs. Almost one-third (30%) of living UK patients have undergone cardiac transplantation. Several patients who have died due to cardiac rejection or post-transplant lymphoproliferative disease had previously undergone cardiac transplantation. Other patients who have died deteriorated too fast to undergo transplantation or died of complications while awaiting transplantation. Neutropenia is another life-threatening issue. Two-thirds of UK patients are treated with granulocyte colony-stimulating factor by subcutaneous injection. Managing neutropenia in this disease is challenging, since patients have highly variable neutrophil counts, which prevents administration of a consistent daily dose and requires repeated blood counts and physician oversight. Exercise intolerance, lethargy and fatigue are universal, interfering with daily life, schoolwork and play and often necessitating use of a wheelchair. Patients cannot perform strenuous or demanding jobs. Many have major feeding problems from infancy through to adult life; for example, requiring feeding via gastrostomies. There can be rapid deterioration during periods of stable health despite expert medical care. Ventricular arrhythmia (tachycardia or fibrillation) affects 10% of adolescents and can cause sudden cardiac death at any time. There are no specific treatments for Barth syndrome. There is no evidence that standard medications for cardiomyopathy ameliorate long-term poor outcomes. Treatment is multidisciplinary and currently limited to treating intercurrent bacterial infections, bone marrow support, physiotherapy, nutritional support, management of heart failure and arrhythmia, and consideration for heart transplantation. Experiments using lymphoblasts from patients with Barth syndrome show that either bezafibrate or resveratrol can partially normalise the deranged cardiolipin ratio. This may be important, since some patients with Barth syndrome who lack neutropenia and tend to have good exercise tolerance have cardiolipin ratios intermediate between those of typical patients and normal individuals. Bezafibrate also improved left ventricular function and showed other benefits at supraphysiological doses in a TAZ knockdown mouse model. This trial was motivated by the need for disease-specific therapy to prevent morbidity, mortality, psychological distress, and disruption of quality of life (QoL) in affected patients and their families. An effective therapy also has the potential to generate savings for the NHS. Bezafibrate is a lipid-lowering drug used in adults and children, with a good safety record in long-term use. These characteristics made it a candidate for investigation. Bezafibrate has been reported to significantly ameliorate a mitochondrial myopathy in adults and shown promising results in several animal/human cellular models of mitochondrial disease. Several of the laboratory assays and clinical investigations proposed in this study were also considered potentially important beyond the scope of this specific study, to assess associations between genotype and phenotype and for future evaluations of therapies in Barth syndrome. Objectives Estimate the effect on clinical, biochemical and QoL outcome measures of bezafibrate compared to placebo. Investigate whether clinical improvements parallel in vitro changes in cardiolipin ratio and mitochondrial morphology in each participant’s cells when cultured with bezafibrate. Investigate whether clinical improvements and culture findings with bezafibrate parallel in vitro changes in each participant’s cells when exposed to resveratrol in laboratory culture. Describe the most feasible methods and standardised outcome measures for future trials. Describe features of the research infrastructure which optimised recruitment, retention and communication with participants and families. Describe participants’ and their families’ perceptions of research and important potential barriers to participation. Methods Study design and participants CARDIOlipin MANipulation trial (CARDIOMAN) was a double-blind, placebo-controlled crossover randomised trial. Treatment was given in two 15-week periods with a minimum of 1 month’s washout period between these when no treatment was given. Twenty-six males and one female with the disease were alive in the UK when the trial was designed. Males aged ≥ 6 years in the UK diagnosed with Barth syndrome were eligible. Exclusion criteria were: hypersensitivity to bezafibrate or component of the investigational medicinal product (IMP), photoallergic or phototoxic reaction to fibrate, unstable cardiac condition, cardiac chamber shortening fraction < 25% or significant decrease in shortening fraction in the preceding year, atrial or ventricular arrhythmia not stabilised by treatment, inability to swallow the IMP, hepatic dysfunction, renal impairment (creatinine clearance < 90 ml/min), gallbladder disease, recent unspecified significant deterioration in general health, prisoners and adults lacking capacity to provide informed consent. Randomisation and masking Participants were randomised to receive either bezafibrate then placebo, or the reverse order. Allocations were generated in advance by the Bristol Trials Centre and provided to the trial pharmacy which dispensed the IMP. All investigators, members of the research team (apart from pharmacy) and participants remained blind to treatment allocation. Intervention and procedures The intervention IMP was bezafibrate taken orally as 100-mg tablets. Children aged 6–9 years started on 100 mg once daily for the first 4 weeks and, if well tolerated, increased to 100 mg twice daily for the remaining 11 weeks. Children aged 10–17 years started on 200 mg once daily for the first 4 weeks and, if well tolerated, increased to 200 mg twice daily for the remaining 11 weeks. Adults (≥ 18 years) took 200 mg twice daily throughout. The comparator IMP was placebo taken orally as visually identical tablets and manufactured to be as similar as possible in taste and smell to the intervention. The IMP was prescribed at the start of the first period and again at the end of the first period for the second period. Outcomes All in vivo outcomes except magnetic resonance spectroscopy (MRS) were assessed three times: at baseline and in the final week of each treatment phase. The primary outcome measure was peak oxygen consumption on bicycle ergometry [peak volume of oxygen (VO2)]. Secondary outcomes were: MLCL/L4-CL ratio and cardiolipin profile in blood cells; phosphocreatine (PCr)/adenosine 5’ triphosphate (ATP) ratio in cardiac muscle on 31P MRS; skeletal muscle oxidative function/on 31P MRS; QoL [age-appropriate Pediatric Quality of Life Inventory (PedsQLTM) questionnaires]; absolute neutrophil count; amino acid expression (serum arginine and cysteine); cardiac function [left and right ventricular function: left ventricular ejection fraction (LVEF%), right ventricular ejection fraction (RVEF%); and 2-D longitudinal and circumferential strain at rest, peak exercise and after recovery]; mitochondrial size and number in lymphocytes; mitochondrial area in lymphocytes and as a proportion of cytoplasm area; mitochondrial function and cristae organisation in lymphocytes/neutrophils; arrhythmia profile from 12-lead electrocardiogram at rest and during exercise. Qualitative research methods explored participants’ and families’ experiences of the different interventions. Adverse events Serious adverse events (SAEs) and non-serious adverse events (AEs) were collected from participants from the time of consent until 1 month after the final period. Participants’ general practitioners were asked to inform the research team of suspected AEs. Participants were asked questions about SAEs/AEs at each research clinic visit and in monthly phone calls, including during the washout period. SAEs were reviewed by the Chief Investigator, who decided whether the SAE was related to bezafibrate. Statistical analysis A total of 20 males aged ≥ 6 years were potentially eligible. The sample size was dictated by the number of eligible boys willing to take part. The primary analysis estimated the difference in mean peak VO2 between placebo and bezafibrate periods (two-tailed 5% significance level). A sample size of 12 participants allowed the trial to detect a difference of 0.90 (within subject) standard deviations with 80% power. The statistical analysis plan (SAP) prespecified that all analyses should be conducted according to the intention-to-treat (ITT) principle. The ITT population comprised all participants and periods, according to the randomised allocations. The safety population comprised all randomised participants, according to the treatment received in each period, who received at least one dose of IMP. All statistical tests were two-sided and used a 5% significance level, except for interactions that used a 10% significance level. Treatment effects were estimated with 95% confidence intervals (CIs). No formal adjustment was made for multiple testing. The treatment effect for the primary outcome was analysed using mixed linear regression models, adjusting for period (fixed effect; exploring interactions where necessary) and participants (random effects). Model assumptions were tested using standard methods, and the carry-over effect was estimated by including treatment order. Treatment effects for continuously scaled secondary outcomes (prespecified in the SAP) were estimated and tested using the same methods. Results There was no statistically significant difference between bezafibrate and placebo in peak VO2, which was 0.66 ml/kg/min lower (95% CI −2.34 to 1.03; p = 0.43) with bezafibrate. There was a borderline statistically significant increase in LVEF% using echocardiography (3.72%, 95% CI −0.26% to 7.69%; p = 0.065) but no evidence of a difference when using magnetic resonance imaging (MRI) (0.15%, 95% CI −3.21% to 3.51%; p = 0.926). There was also no difference for RVEF% between bezafibrate and placebo (0.32, 95% CI −2.32 to 2.96; p = 0.801). Longitudinal and circumferential strain at rest were better (lower) with bezafibrate than with placebo; differences were –1.67 (95% CI −3.11 to −0.22; p = 0.026) and −2.72 (95% CI −5.03 to −0.40; p = 0.024) respectively. There was no difference in diastolic ratio at rest between bezafibrate and placebo, and no differences in strain or diastolic ratio at peak exercise or after 2 minutes’ recovery. All participants had sinus rhythm at rest and during exercise for all three time points. Magnetic resonance spectroscopy was only performed after the second period for 10 participants. PCr/ATP ratio in cardiac muscle was not collected. Cross-sectionally (five vs. five participants), MRS appeared to increase Tau and reduce Qmax parameters with bezafibrate compared to placebo. Monolysocardiolipin/L4-CL ratio did not differ between bezafibrate and placebo but deteriorated in the second period (20% higher, 95% CI 3% to 40%; p = 0.024). Neutrophil count also showed no difference between bezafibrate and placebo but increased in the second period (2.26, 95% CI 0.08 to 4.45; p = 0.043). Plasma cysteine increased with bezafibrate (32% higher, 95% CI 8% to 62%; p = 0.001) but plasma arginine did not (25% higher, 95% CI −10% to 72%; p = 0.180). Mitochondrial outcomes on blood samples did not show marked differences and were not formally compared. Quality-of-life scores were transformed to a 0–100 scale (higher being better). Bezafibrate had no effect on core (−3.41, 95% CI −8.67 to 1.86; p = 0.192) or fatigue (1.71, 95% CI −6.28 to 9.71; p = 0.659) QoL scores. Emerging themes identified in qualitative interviews were classified as overarching, related to lived experience with Barth syndrome, and trial participation and conduct. Participants and families were pleased to take part in the trial, viewing participation as ‘giving back’ to the medical community. No participant withdrew, and the trial was not perceived to be too onerous for families. Participating in the research gave both individuals and families a sense of responsibility for their condition, partly driven by appreciation for the Barth Syndrome Service and staff expertise. Monolysocardiolipin/L4-CL ratio in vitro was estimated from samples of cells incubated with control, bezafibrate or resveratrol. Each drug reduced the MLCL/L4-CL ratio, largely by increasing intermediate cardiolipin species, and more so with resveratrol than with bezafibrate. Ratios were nevertheless profoundly abnormal in comparison to patients with intermediate Barth phenotypes. Discussion Main findings: study results There was no clinically important or statistically significant improvement in peak VO2 with bezafibrate compared to placebo. There were inconsistent findings for LVEF% by method of measurement; echocardiography showed a borderline improvement that cardiac MRI did not demonstrate. Longitudinal and circumferential strain measurements were better at rest with bezafibrate, but not at peak exercise. There were no clinically important or statistically significant improvements in core or fatigue QoL domains. Plasma cysteine was significantly improved with bezafibrate treatment. Plasma arginine also increased but not significantly. Neutrophil count was unaffected and there was no significant change in cardiolipin ratio in participants’ blood with bezafibrate. There were no significant period effects except for MLCL/L4-CL ratio and neutrophil count, both increased in the second period. In vitro incubation of Epstein–Barr virus-transformed patient lymphoblasts with either bezafibrate or resveratrol resulted in improved MLCL/L4-CL ratios, an effect that was more profound with resveratrol. Treatment with this drug also resulted in a more obvious increase in intermediate MLCL species. Strengths and limitations Strengths of the trial are: randomisation and placebo blinding; crossover design; excellent retention; completeness of the data, good adherence and IMP tolerance. There were several limitations. The sample size (outside our control) was very small, and interpretation of effects for many secondary outcomes was challenging. Longer treatment duration or a higher bezafibrate dose might have produced better outcomes. Bezafibrate may have induced adverse reactions in some participants, inadvertently causing unblinding. The group of participants randomised to receive bezafibrate first was older than the group randomised to the opposite order, which may explain period effects. The electron microscopic and mitochondrial assessments proved problematic and were not completed in vitro. Measurements of mitochondrial content and membrane potential were highly variable. Amino acid levels were not assayed after fasting. Echocardiography images during exercise testing were often suboptimal. Lessons for the future Magnetic resonance spectroscopy in children is still exploratory, and protocols need to be better validated, but it is considered very promising as a potential objective functional outcome. Cardiolipin profile is not a good outcome for research, although it is appropriate for diagnosis because the Barth cardiolipin profile is so extremely different from a normal profile. Electron microscopy measurements of mitochondria should not be considered as outcomes in future trials. Peak VO2 should be the preferred current primary outcome because it is resistant to bias compared to other functional outcomes. Conclusion The trial did not show a significant treatment effect for the primary outcome, peak VO2. Some secondary outcomes such as systolic function measured by echocardiography and amino acid levels provided some evidence of benefit. The trial provided insights about trial methods and conduct in the context of a very rare paediatric disease that should inform future studies. Trial registration This trial is registered as ISRCTN58006579. Funding This award was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation (EME) programme (NIHR award ref: 12/205/56) and is published in full in Efficacy and Mechanism Evaluation; Vol. 11, No. 13. See the NIHR Funding and Awards website for further award information.

Cardiolipin (CL) is a unique, four-chain phospholipid synthesized in the inner mitochondrial membrane (IMM). The acyl chain composition of CL is regulated through a remodeling pathway, whose loss causes mitochondrial dysfunction in Barth syndrome (BTHS). Yeast has been used extensively as a model system to characterize CL metabolism, but mutants lacking its two remodeling enzymes, Cld1p and Taz1p, exhibit mild structural and respiratory phenotypes compared to mammalian cells. Here, we show an essential role for CL remodeling in the structure and function of the IMM in yeast grown under reduced oxygenation. Microaerobic fermentation, which mimics natural yeast environments, caused the accumulation of saturated fatty acids and, under these conditions, remodeling mutants showed a loss of IMM ultrastructure. We extended this observation to HEK293 cells, where phospholipase A2 inhibition by Bromoenol lactone resulted in respiratory dysfunction and cristae loss upon mild treatment with exogenous saturated fatty acids. In microaerobic yeast, remodeling mutants accumulated unremodeled, saturated CL, but also displayed reduced total CL levels, highlighting the interplay between saturation and CL biosynthesis and/or breakdown. We identified the mitochondrial phospholipase A1 Ddl1p as a regulator of CL levels, and those of its precursors phosphatidylglycerol and phosphatidic acid, under these conditions. Loss of Ddl1p partially rescued IMM structure in cells unable to initiate CL remodeling and had differing lipidomic effects depending on oxygenation. These results introduce a revised yeast model for investigating CL remodeling and suggest that its structural functions are dependent on the overall lipid environment in the mitochondrion.

Barth syndrome (BTHS) is a mitochondrial lipid disorder caused by mutations in TAFAZZIN (TAZ), required for cardiolipin (CL) remodeling. Cardiomyopathy is a major clinical feature, with no curative therapy. Linoleic acid (LA) supplementation is proposed to ameliorate BTHS cardiomyopathy by enhancing linoleoyl group incorporation into CL. While the beneficial effect of dietary LA supplementation in delaying the development of BTHS cardiomyopathy has been recently tested, its potential to reverse established BTHS cardiomyopathy remains unclear. Our study revealed that LA supplementation cannot rescue established BTHS cardiomyopathy in mice, highlighting the importance of early initiation of LA supplementation for maximum benefits.

Objective. This study examined the preliminary reliability and validity of the PedsQL™ Family Impact Module (PedsQL FIM) in families of children with Barth syndrome (BTHS). Method. A total of 72 parents with children or youth between the ages of 5 and 19 participated in this study. Thirty-three parents of children with BTHS and 39 parents of unaffected children completed the PedsQL FIM and a demographic information form. Internal consistency reliability and item-total correlations were calculated to test the reliability of the PedsQL FIM. Construct validity was examined using the known-groups method. We estimated the mean score differences of the PedsQL FIM between the two groups using three different models, including unadjusted, multivariate regression, and propensity score matching with inverse probability of treatment weighting (PS-IPTW) models. Results. The Cronbach's alpha coefficients were greater than 0.70 for all scales of the PedsQL FIM, except for the communication scale. The item-total correlations were significant for all scales with moderate to high correlations (p <.05). In construct validity, the mean scores of the PedsQL FIM between the two groups were significantly different (p <.05) for all scales and total score in the unadjusted and PS-IPTW models. However, in the multivariate regression model, the family relationships scale was not significant between the two groups. Conclusion. The PedsQL FIM demonstrated adequate measurement properties of preliminary reliability and validity in assessing the impact of children with BTHS on parental health-related quality of life (HRQoL) and family functioning. Further research needs to be conducted to examine the psychometric properties of the PedsQL FIM with a large sample of BTHS and with other pediatric rare diseases. [ABSTRACT FROM AUTHOR]

Barth Syndrome (BTHS) is a rare X-linked disease, characterized clinically by cardiomyopathy, skeletal myopathy, neutropenia, and growth retardation. BTHS is caused by mutations in the phospholipid acyltransferase tafazzin (Gene: TAFAZZIN, TAZ). Tafazzin catalyzes the final step in the remodeling of cardiolipin (CL), a glycerophospholipid located in the inner mitochondrial membrane. As the phospholipid composition strongly determines membrane properties, correct biosynthesis of CL and other membrane lipids is essential for mitochondrial function. Mitochondria provide 95% of the energy demand in the heart, particularly due to their role in fatty acid oxidation. Alterations in lipid homeostasis in BTHS have an impact on mitochondrial membrane proteins and thereby contribute to cardiomyopathy. We analyzed a transgenic TAFAZZIN-knockdown (TAZ-KD) BTHS mouse model and determined the distribution of 193 individual lipid species in TAZ-KD and WT hearts at 10 and 50 weeks of age, using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Our results revealed significant lipid composition differences between the TAZ-KD and WT groups, indicating genotype-dependent alterations in most analyzed lipid species. Significant changes in the myocardial lipidome were identified in both young animals without cardiomyopathy and older animals with heart failure. Notable alterations were found in phosphatidylcholine (PC), phosphatidylethanolamine (PE), lysophosphatidylethanolamine (LPE), lysophosphatidylcholine (LPC) and plasmalogen species. PC species with 2–4 double bonds were significantly increased, while polyunsaturated PC species showed a significant decrease in TAZ-KD mice. Furthermore, Linoleic acid (LA, 18:2) containing PC and PE species, as well as arachidonic acid (AA, 20:4) containing PE 38:4 species are increased in TAZ-KD. We found higher levels of AA containing LPE and PE-based plasmalogens (PE P-). Furthermore, we are the first to show significant changes in sphingomyelin (SM) and ceramide (Cer) lipid species Very long-chained SM species are accumulating in TAZ-KD hearts, whereas long-chained Cer and several hexosyl ceramides (HexCer) species accumulate only in 50-week-old TAZ-KD hearts These findings offer potential avenues for the diagnosis and treatment of BTHS, presenting new possibilities for therapeutic approaches.

Abstract Mitochondria are central for cellular metabolism and energy supply. Barth syndrome (BTHS) is a severe disorder, due to dysfunction of the mitochondrial cardiolipin acyl transferase tafazzin. Altered cardiolipin remodeling affects mitochondrial inner membrane organization and function of membrane proteins such as transporters and the oxidative phosphorylation (OXPHOS) system. Here, we describe a mouse model that carries a G197V exchange in tafazzin, corresponding to BTHS patients. TAZG197V mice recapitulate disease‐specific pathology including cardiac dysfunction and reduced oxidative phosphorylation. We show that mutant mitochondria display defective fatty acid‐driven oxidative phosphorylation due to reduced levels of carnitine palmitoyl transferases. A metabolic switch in ATP production from OXPHOS to glycolysis is apparent in mouse heart and patient iPSC cell‐derived cardiomyocytes. An increase in glycolytic ATP production inactivates AMPK causing altered metabolic signaling in TAZG197V. Treatment of mutant cells with AMPK activator reestablishes fatty acid‐driven OXPHOS and protects mice against cardiac dysfunction.

Purpose: Barth syndrome (BTHS; OMIM #302060) is a rare disease characterized by cardiolipin abnormalities and cardiomyopathy, intermittent neutropenia and skeletal myopathy among other defects. Elamipretide is an investigational drug that binds to cardiolipin, resulting in improved membrane stability, cellular respiration, and adenosine triphosphate production. This case report seeks to provide guidance to clinicians for the effective use of elamipretide when managing BTHS patients. Methods: Here, we report an 11-month-old male requiring cardiopulmonary resuscitation and intubation on initial presentation. Echocardiogram showed a dilated left ventricle (LV) with severely diminished systolic LV function. The patient was placed on venoarterial extracorporeal membrane oxygenation (ECMO) due to a low cardiac output state. Within about two weeks of hospitalization, a diagnosis of BTHS was confirmed on rapid exome sequencing; daily elamipretide therapy (5 mg) was initiated. Results: The patient was decannulated from ECMO. Due to failing extubation, a Berlin Heart EXCOR left ventricular assist device (LVAD) was placed on hospital-day 29. Approximately five months later, echocardiogram demonstrated a marked improvement in LVEF (18% to 54%), with cardiac catheterization during pause of LVAD support indicating hemodynamic parameters favorable for LVAD explantation. He underwent successful LVAD explantation and was removed from the cardiac transplant list. The patient was discharged from the hospital and has remained stable on daily elamipretide therapy. Conclusion: In previous studies, elamipretide therapy has demonstrated normalization of mitochondrial function alongside improvement in LV function. Observations made in our case support these findings and emphasize the need for readily available, targeted therapies in BTHS patients.

Barth Syndrome (BTHS) is an inherited cardiomyopathy caused by defects in the mitochondrial transacylase TAFAZZIN (Taz), required for the synthesis of the phospholipid cardiolipin. BTHS is characterized by heart failure, increased propensity for arrhythmias and a blunted inotropic reserve. Defects in Ca2+-induced Krebs cycle activation contribute to these functional defects, but despite oxidation of pyridine nucleotides, no oxidative stress developed in the heart. Here, we investigated how retrograde signaling pathways orchestrate metabolic rewiring to compensate for mitochondrial defects. In mice with an inducible knockdown (KD) of TAFAZZIN, and in induced pluripotent stem cell-derived cardiac myocytes, mitochondrial uptake and oxidation of fatty acids was strongly decreased, while glucose uptake was increased. Unbiased transcriptomic analyses revealed that the activation of the eIF2α/ATF4 axis of the integrated stress response upregulates one-carbon metabolism, which diverts glycolytic intermediates towards the biosynthesis of serine and fuels the biosynthesis of glutathione. In addition, strong upregulation of the glutamate/cystine antiporter xCT increases cardiac cystine import required for glutathione synthesis. Increased glutamate uptake facilitates anaplerotic replenishment of the Krebs cycle, sustaining energy production and antioxidative pathways. These data indicate that ATF4-driven rewiring of metabolism compensates for defects in mitochondrial uptake of fatty acids to sustain energy production and antioxidation. [ABSTRACT FROM AUTHOR]

Purpose: Barth syndrome (BTHS) is a rare genetic disorder characterized by skeletal myopathy, cardiomyopathy, and exercise intolerance due to early fatigue. The purpose of this study was to test the feasibility and validity of a new phone application designed to capture multi-dimensional aspects of fatigue across the lifespan. The specific study aims were to (1) assess the feasibility of using the app to record perceived fatigue levels in real-time, (2) evaluate discriminant validity by assessing if the app can differentiate between those with and without BTHS, and (3) content validity by assessing the relationship between perceived energy levels and actual energy expenditure. Methods: Eighteen participants with BTHS and 18 age-matched control participants completed the study. The participants wore an activity tracker for 14 days and were prompted to respond to an Android app to report their fatigue levels 6 × /day. Statistical analysis was completed to examine perceived fatigue and the relationship between reported fatigue and actual energy expenditure. Results: Feasibility was supported by the majority of participants responding to at least 50% of the application prompts and scores indicative of good internal consistency between responses (92–95%) and reliability of the battery scale (p <.001). Discriminant validity of the app was only partially supported, with the number of "crashes" being significantly different between those with and without BTHS (p = 0.042). Other measures of perceived fatigue were not found to be significantly different between groups, even though individuals with BTHS showed significantly lower energy expenditure than control participants during the day as measured by actigraphy (p < 0.001). Content validity of the app was supported, with perceived energy levels significantly correlating with actual energy expenditure collected with the activity tracker (p < 0.001). Conclusions: In summary, the phone app developed by our team allowed researchers to capture the lived experience of individuals with BTHS while also capturing objective data. We verified that the app was able to consistently and accurately capture participant-reported fatigue. The battery scale tested as part of our feasibility aim was successful in capturing perceived levels of energy and can be used as a valid measure of fatigue in future studies. It was interesting to note that "crashes" appear to be the main differentiating factor in fatigue between the BTHS and control participants, where other measures of perceived fatigue were not found to be significantly different. These results highlight the complex nature of measuring fatigue as a subjective construct. This study provides foundational information on methods for quantifying fatigue in adults, adolescents, and children with BTHS and can provide possible targets for future therapeutic trials. [ABSTRACT FROM AUTHOR]

Introduction: The promising potential of adeno-associated virus (AAV) gene delivery strategies to treat genetic disorders continues to grow with an additional three AAV-based therapies recently approved by the Food and Drug Administration and dozens of others currently under evaluation in clinical trials. With these developments, it has become increasingly apparent that the high doses currently needed for efficacy carry risks of toxicity and entail enormous manufacturing costs, especially for clinical grade products. Strategies to increase the therapeutic efficacy of AAV-mediated gene delivery and reduce the minimal effective dose would have a substantial impact on this field. We hypothesized that an exercise-induced redistribution of tissue perfusion in the body to favor specific target organs via acute aerobic exercise prior to systemic intravenous (IV) AAV administration could increase efficacy. Background: Aerobic exercise triggers an array of downstream physiological effects including increased perfusion of heart and skeletal muscle, which we expected could enhance AAV transduction. Prior preclinical studies have shown promising results for a gene therapy approach to treat Barth syndrome (BTHS), a rare monogenic cardioskeletal myopathy, and clinical studies have shown the benefit of low intensity exercise in these patients, making this a suitable disease in which to test the ability of aerobic exercise to enhance AAV transduction. Methods: Wild-type (WT) and BTHS mice were either systemically administered AAV9 or completed one episode of low intensity treadmill exercise immediately prior to systemic administration of AAV9. Results: We demonstrate that a single episode of acute low intensity aerobic exercise immediately prior to IV AAV9 administration improves marker transgene delivery in WT mice as compared to mice injected without the exercise pre-treatment. In BTHS mice, prior exercise improved transgene delivery and additionally increased improvement in mitochondrial gene transcription levels and mitochondrial function in the heart and gastrocnemius muscles as compared to mice treated without exercise. Conclusions: Our findings suggest that one episode of acute low intensity aerobic exercise improves AAV9 transduction of heart and skeletal muscle. This low-risk, cost effective intervention could be implemented in clinical trials of individuals with inherited cardioskeletal disease as a potential means of improving patient safety for human gene therapy. [ABSTRACT FROM AUTHOR]

Studies of rare human genetic disorders of mitochondrial phospholipid metabolism have highlighted the crucial role that membrane phospholipids play in mitochondrial bioenergetics and human health. The phospholipid composition of mitochondrial membranes is highly conserved from yeast to humans, with each class of phospholipid performing a specific function in the assembly and activity of various mitochondrial membrane proteins, including the oxidative phosphorylation complexes. Recent studies have uncovered novel roles of cardiolipin and phosphatidylethanolamine, two crucial mitochondrial phospholipids, in organismal physiology. Studies on inter-organellar and intramitochondrial phospholipid transport have significantly advanced our understanding of the mechanisms that maintain mitochondrial phospholipid homeostasis. Here, we discuss these recent advances in the function and transport of mitochondrial phospholipids while describing their biochemical and biophysical properties and biosynthetic pathways. Additionally, we highlight the roles of mitochondrial phospholipids in human health by describing the various genetic diseases caused by disruptions in their biosynthesis and discuss advances in therapeutic strategies for Barth syndrome, the best-studied disorder of mitochondrial phospholipid metabolism. [ABSTRACT FROM AUTHOR]

Mitochondria are central for cellular metabolism and energy supply. Barth syndrome (BTHS) is a severe disorder, due to dysfunction of the mitochondrial cardiolipin acyl transferase tafazzin. Altered cardiolipin remodeling affects mitochondrial inner membrane organization and function of membrane proteins such as transporters and the oxidative phosphorylation (OXPHOS) system. Here, we describe a mouse model that carries a G197V exchange in tafazzin, corresponding to BTHS patients. TAZG197V mice recapitulate disease‐specific pathology including cardiac dysfunction and reduced oxidative phosphorylation. We show that mutant mitochondria display defective fatty acid‐driven oxidative phosphorylation due to reduced levels of carnitine palmitoyl transferases. A metabolic switch in ATP production from OXPHOS to glycolysis is apparent in mouse heart and patient iPSC cell‐derived cardiomyocytes. An increase in glycolytic ATP production inactivates AMPK causing altered metabolic signaling in TAZG197V. Treatment of mutant cells with AMPK activator reestablishes fatty acid‐driven OXPHOS and protects mice against cardiac dysfunction. Synopsis: Defective cardiolipin remodeling due to mutation in tafazzin, causes Barth syndrome (BTHS) with cardiac impairment and reduced oxidative phosphorylation. Dysfunctional FAO‐driven OXPHOS due to altered AMPK signaling is restored in BTHS models by treatment with AMPK activator. The characteristic pathology observed in Barth syndrome patients is mirrored by TAZG197V mice, which are characterized by severe cardiac dysfunction and reduced oxidative phosphorylation.A switch in the metabolic pathways from oxidative phosphorylation to glycolysis for compensating ATP production is evident in TAZG197V mutants.Due to metabolic shift and increased ATP, AMPK pathway is shut down affecting transcription of CPTs with reduced fatty acid oxidation, a known consequence of heart failure.Functional restoration of cardiac function in TAZG197V mice is reestablished by treating mutant mice with an AMPK activator, which restores fatty acid‐driven oxidative phosphorylation in the heart. [ABSTRACT FROM AUTHOR]

Simple Summary: Barth syndrome (BTHS) is a disease that affects energy production. It results from mutations on the X chromosome, and thus it mainly affects males since they have only one copy (females have two X chromosomes). Although BTHS is rare, the consequences can be severe. BTHS affects the heart, immune system, and muscles, so boys and men with BTHS are at a high risk of heart attacks and death from infections, and they tire easily, which impacts quality of life. Women with one mutated X chromosome are typically thought to be asymptomatic, so they have not been studied very much. However, in other diseases caused by X chromosome mutations, females that were thought to be healthy developed symptoms after they got older. In this work, we studied female mice with one mutated X chromosome, which are models of female carriers of BTHS. We found that with advancing age, the carriers have some slowdown in their running speed, which is like that seen in male mice but less severe. They also weigh less and are better able to maintain their blood sugar, which could be beneficial. Our work shows that female carriers can have symptoms and supports further research in women. Barth syndrome (BTHS) is caused by mutations in tafazzin resulting in deficits in cardiolipin remodeling that alter major metabolic processes. The tafazzin gene is encoded on the X chromosome, and therefore BTHS primarily affects males. Female carriers are typically considered asymptomatic, but age-related changes have been reported in female carriers of other X-linked disorders. Therefore, we examined the phenotype of female mice heterozygous for deletion of the tafazzin gene (Taz-HET) at 3 and 12 months of age. Food intakes, body masses, lean tissue and adipose depot weights, daily activity levels, metabolic measures, and exercise capacity were assessed. Age-related changes in mice resulted in small but significant genotype-specific differences in Taz-HET mice compared with their female Wt littermates. By 12 months, Taz-HET mice weighed less than Wt controls and had smaller gonadal, retroperitoneal, and brown adipose depots and liver and brain masses, despite similar food consumption. Daily movement, respiratory exchange ratio, and total energy expenditure did not vary significantly between the age-matched genotypes. Taz-HET mice displayed improved glucose tolerance and insulin sensitivity at 12 months compared with their Wt littermates but had evidence of slightly reduced exercise capacity. Tafazzin mRNA levels were significantly reduced in the cardiac muscle of 12-month-old Taz-HET mice, which was associated with minor but significant alterations in the heart cardiolipin profile. This work is the first to report the characterization of a model of female carriers of heterozygous tafazzin deficiency and suggests that additional study, particularly with advancing age, is warranted. [ABSTRACT FROM AUTHOR]

BackgroundCardiomyopathy is a major clinical feature in Barth syndrome (BTHS), an X-linked mitochondrial lipid disorder caused by mutations in Tafazzin (TAZ), encoding a mitochondrial acyltransferase required for cardiolipin remodeling. Despite recent description of a mouse model of BTHS cardiomyopathy, an in-depth analysis of specific lipid abnormalities and mitochondrial form and function in an in vivo BTHS cardiomyopathy model is lacking.MethodsWe performed in-depth assessment of cardiac function, cardiolipin species profiles, and mitochondrial structure and function in our newly generated Taz cardiomyocyte-specific knockout mice and Cre-negative control mice (n≥3 per group).ResultsTaz cardiomyocyte-specific knockout mice recapitulate typical features of BTHS and mitochondrial cardiomyopathy. Fewer than 5% of cardiomyocyte-specific knockout mice exhibited lethality before 2 months of age, with significantly enlarged hearts. More than 80% of cardiomyocyte-specific knockout displayed ventricular dilation at 16 weeks of age and survived until 50 weeks of age. Full parameter analysis of cardiac cardiolipin profiles demonstrated lower total cardiolipin concentration, abnormal cardiolipin fatty acyl composition, and elevated monolysocardiolipin to cardiolipin ratios in Taz cardiomyocyte-specific knockout, relative to controls. Mitochondrial contact site and cristae organizing system and F1F0-ATP synthase complexes, required for cristae morphogenesis, were abnormal, resulting in onion-shaped mitochondria. Organization of high molecular weight respiratory chain supercomplexes was also impaired. In keeping with observed mitochondrial abnormalities, seahorse experiments demonstrated impaired mitochondrial respiration capacity.ConclusionsOur mouse model mirrors multiple physiological and biochemical aspects of BTHS cardiomyopathy. Our results give important insights into the underlying cause of BTHS cardiomyopathy and provide a framework for testing therapeutic approaches to BTHS cardiomyopathy, or other mitochondrial-related cardiomyopathies.

Abstract Background Barth syndrome (BTHS) is a rare genetic disease that is characterized by cardiomyopathy, skeletal myopathy, neutropenia, and growth abnormalities and often leads to death in childhood. Recently, elamipretide has been tested as a potential first disease-modifying drug. This study aimed to identify patients with BTHS who may respond to elamipretide, based on continuous physiological measurements acquired through wearable devices. Results Data from a randomized, double-blind, placebo-controlled crossover trial of 12 patients with BTHS were used, including physiological time series data measured using a wearable device (heart rate, respiratory rate, activity, and posture) and functional scores. The latter included the 6-minute walk test (6MWT), Patient-Reported Outcomes Measurement Information System (PROMIS) fatigue score, SWAY Balance Mobile Application score (SWAY balance score), BTHS Symptom Assessment (BTHS-SA) Total Fatigue score, muscle strength by handheld dynamometry, 5 times sit-and-stand test (5XSST), and monolysocardiolipin to cardiolipin ratio (MLCL:CL). Groups were created through median split of the functional scores into “highest score” and “lowest score”, and “best response to elamipretide” and “worst response to elamipretide”. Agglomerative hierarchical clustering (AHC) models were implemented to assess whether physiological data could classify patients according to functional status and distinguish non-responders from responders to elamipretide. AHC models clustered patients according to their functional status with accuracies of 60–93%, with the greatest accuracies for 6MWT (93%), PROMIS (87%), and SWAY balance score (80%). Another set of AHC models clustered patients with respect to their response to treatment with elamipretide with perfect accuracy (all 100%). Conclusions In this proof-of-concept study, we demonstrated that continuously acquired physiological measurements from wearable devices can be used to predict functional status and response to treatment among patients with BTHS.

Mutations in the mitochondrial-DNA or mitochondria related nuclear-encoded-DNA lead to various multisystemic disorders collectively termed mitochondrial diseases. One in three cases of mitochondrial disease affects the heart muscle, which is called mitochondrial cardiomyopathy (MCM) and is associated with hypertrophic, dilated, and noncompact cardiomyopathy. The heart is an organ with high energy demand, and mitochondria occupy 30%–40% of its cardiomyocyte-cell volume. Mitochondrial dysfunction leads to energy depletion and has detrimental effects on cardiac performance. However, disease development and progression in the context of mitochondrial and nuclear DNA mutations, remains incompletely understood. The system of induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CM) is an excellent platform to study MCM since the unique genetic identity to their donors enables a robust recapitulation of the predicted phenotypes in a dish on a patient-specific level. Here, we focus on recent insights into MCM studied by patient-specific iPSC-CM and further discuss research gaps and advances in metabolic maturation of iPSC-CM, which is crucial for the study of mitochondrial dysfunction and to develop novel therapeutic strategies.

Barth Syndrome, a rare X-linked disorder affecting 1:300,000 live births, results from defects in Tafazzin, an acyltransferase that remodels cardiolipin and is essential for mitochondrial respiration. Barth Syndrome patients develop cardiomyopathy, muscular hypotonia and cyclic neutropenia during childhood, rarely surviving to middle age. At present, no effective therapy exists, and downstream transcriptional effects of Tafazzin dysfunction are incompletely understood. To identify novel, cell-specific, pathological pathways that mediate heart dysfunction, we performed single-nucleus RNA-sequencing (snRNA-seq) on wild-type (WT) and Tafazzin-knockout (Taz-KO) mouse hearts. We determined differentially expressed genes (DEGs) and inferred predicted cell–cell communication networks from these data. Surprisingly, DEGs were distributed heterogeneously across the cell types, with fibroblasts, cardiomyocytes, endothelial cells, macrophages, adipocytes and pericytes exhibiting the greatest number of DEGs between genotypes. One differentially expressed gene was detected for the lymphatic endothelial and mesothelial cell types, while no significant DEGs were found in the lymphocytes. A Gene Ontology (GO) analysis of these DEGs showed cell-specific effects on biological processes such as fatty acid metabolism in adipocytes and cardiomyocytes, increased translation in cardiomyocytes, endothelial cells and fibroblasts, in addition to other cell-specific processes. Analysis of ligand–receptor pair expression, to infer intercellular communication patterns, revealed the strongest dysregulated communication involved adipocytes and cardiomyocytes. For the knockout hearts, there was a strong loss of ligand–receptor pair expression involving adipocytes, and cardiomyocyte expression of ligand–receptor pairs underwent reorganization. These findings suggest that adipocyte and cardiomyocyte mitochondria may be most sensitive to mitochondrial Tafazzin deficiency and that rescuing adipocyte mitochondrial dysfunction, in addition to cardiomyocyte mitochondrial dysfunction, may provide therapeutic benefit in Barth Syndrome patients. [ABSTRACT FROM AUTHOR]

Barth syndrome (BTHS) is an X‐linked disorder characterized by cardiomyopathy, skeletal myopathy, and 3‐methylglutaconic aciduria. The causative pathogenic variants for BTHS are in TAZ, which encodes a putative acyltransferase named tafazzin and is involved in the remodeling of cardiolipin in the inner mitochondrial membranes. Pathogenic variants in TAZ result in mitochondrial structural and functional abnormalities. We report a case of infantile BTHS with severe heart failure, left ventricular noncompaction, and lactic acidosis, having a missense c.640C>T (p.His214Tyr) variant in TAZ, which is considered a pathogenic variant based on the previously reported amino acid substitution at the same site (c.641A>G, p.His214Arg). However, in this previously reported case, heart function was compensated and not entirely similar to the present case. Silico prediction analysis suggested that c.640C>T could alter the TAZ messenger RNA (mRNA) splicing process. TAZ mRNAs in isolated peripheral mononuclear cells from the patient and in vitro splicing analysis using minigenes of TAZ found an 8 bp deletion at the 3′ end of exon 8, which resulted in the formation of a termination codon in the coding region of exon 9 (H214Nfs*3). These findings suggest that splicing abnormalities should always be considered in BTHS. [ABSTRACT FROM AUTHOR]

Tafazzin, which is encoded by the TAZ gene, catalyzes transacylation to form mature cardiolipin and shows preference for the transfer of a linoleic acid (LA) group from phosphatidylcholine (PC) to monolysocardiolipin (MLCL) with influence from mitochondrial membrane curvature. The protein contains domains and motifs involved in targeting, anchoring, and an active site for transacylase activity. Tafazzin activity affects many aspects of mitochondrial structure and function, including that of the electron transport chain, fission-fusion, as well as apoptotic signaling. TAZ mutations are implicated in Barth syndrome, an underdiagnosed and devastating disease that primarily affects male pediatric patients with a broad spectrum of disease pathologies that impact the cardiovascular, neuromuscular, metabolic, and hematologic systems.

Abstract Several mitochondrial diseases are caused by pathogenic variants that impair membrane phospholipid remodeling, with no FDA‐approved therapies. Elamipretide targets the inner mitochondrial membrane where it binds to cardiolipin, resulting in improved membrane stability, cellular respiration, and ATP production. In clinical trials, elamipretide produced clinical and functional improvements in adults and adolescents with mitochondrial disorders, such as primary mitochondrial myopathy and Barth syndrome; however, experience in younger patients is limited and to our knowledge, these are the first case reports on the safety and efficacy of elamipretide treatment in children under 12 years of age. We describe the use of elamipretide in patients with mitochondrial disorders to provide dosing parameters in patients aged

Abstract Background Natural history studies are increasingly recognized as having an important role in drug development for rare diseases. A phase 3, observational, retrospective, and non-interventional study was designed to establish a natural history control (NHC) cohort of patients with Barth syndrome (BTHS) to provide further analysis of the efficacy of elamipretide observed in an open-label extension (OLE) phase of the TAZPOWER trial, a clinical trial that tested the efficacy of 40 mg daily of elamipretide in patients with BTHS. Methods This was a retrospective, non-interventional study. A propensity score model was used to compare elamipretide-treated patients and NHCs. The analysis included 8 patients from the TAZPOWER OLE and 19 untreated NHCs (including 12 with serial echocardiographic assessments). Results For the 6-min walk test (6MWT, primary endpoint), the least squares (LS) mean difference between groups was 79.7 m (P = 0.0004) at week 64 and 91.0 m (P = 0.0005) at week 76 in favor of elamipretide. Significant improvements in muscle strength (secondary endpoint), as assessed by handheld dynamometry (HHD) were also observed with elamipretide, with LS mean differences of 40.8 Newtons at 64 weeks (P = 0.0002) and 56.7 Newtons at 76 weeks (P = 0.0005). Patients continuously treated with elamipretide also experienced statistically significant improvements in other secondary endpoints (i.e., 5 times sit-to-stand [5XSST], multi-domain responder index [MDRI]). The functional improvements were robust to sensitivity analyses. Left ventricular stroke volume increased from baseline in patients with elamipretide but decreased in NHCs. Conclusions Overall, the study established a NHC for use in assessing the efficacy of therapeutic interventions in patients with BTHS and the results suggest that elamipretide may improve natural history of BTHS at least in part by attenuating the natural decline in heart function and provide meaningful improvements in heart function and functional capacity in patients with BTHS compared to NHCs. Highlights A matched Natural History Control (NHC) was used to evaluate elamipretide in BTHS Elamipretide may improve natural history of BTHS by attenuating natural decline in heart function Elamipretide was associated with meaningful clinical improvements in skeletal muscle and cardiovascular parameters that were not observed in NHCs The study established a NHC for use in assessing the efficacy of therapeutic interventions in BTHS

Simple Summary: Barth Syndrome (BTHS) is a rare X-linked genetic disease in which some patients suffer from severe infections due to neutrophil dysfunction. B cells produce cytokines that attract neutrophils to sites of infection. Here, we examined if B cells from BTHS patients exhibited a reduced ability to express chemokine (C-X-C motif) ligand 1 (CXCL1), a known chemoattractant for neutrophils. We show that B cells from BTHS patients exhibit lowered expression of CXCL1 when stimulated with bacteria compared to control cells. Our findings suggest that an impaired ability of B cells to produce cytokines might contribute to infections in some BTHS patients. Barth Syndrome (BTHS) is a rare X-linked genetic disease caused by a mutation in the TAFAZZIN gene, which codes for the protein tafazzin involved in cardiolipin remodeling. Approximately 70% of patients with BTHS exhibit severe infections due to neutropenia. However, neutrophils from BTHS patients have been shown to exhibit normal phagocytosis and killing activity. B lymphocytes play a crucial role in the regulation of the immune system and, when activated, secrete cytokines known to attract neutrophils to sites of infection. We examined the expression of chemokine (C-X-C motif) ligand 1 (CXCL1), a known chemotactic for neutrophils, in Epstein–Barr virus transformed control and BTHS B lymphoblasts. Age-matched control and BTHS B lymphoblasts were incubated with Pseudomonas aeruginosa for 24 h and then cell viability, CD27+, CD24+, CD38+, CD138+ and PD1+ surface marker expression and CXCL1 mRNA expression determined. Cell viability was maintained in lymphoblasts incubated in a ratio of 50:1 bacteria:B cells. Surface marker expression was unaltered between control and BTHS B lymphoblasts. In contrast, CXCL1 mRNA expression was reduced approximately 70% (p < 0.05) in untreated BTHS B lymphoblasts compared to control and approximately 90% (p < 0.05) in bacterial treated BTHS B lymphoblasts compared to the control. Thus, naïve and bacterial-activated BTHS B lymphoblasts exhibit reduced mRNA expression of the neutrophil chemoattractant factor CXCL1. We suggest that impaired bacterial activation of B cells in some BTHS patients could influence neutrophil function via impairing neutrophil recruitment to sites of infection and this could potentially contribute to these infections. [ABSTRACT FROM AUTHOR]

Background: Barth syndrome (BTHS) is a rare genetic disease that is characterized by cardiomyopathy, skeletal myopathy, neutropenia, and growth abnormalities and often leads to death in childhood. Recently, elamipretide has been tested as a potential first disease-modifying drug. This study aimed to identify patients with BTHS who may respond to elamipretide, based on continuous physiological measurements acquired through wearable devices. Results: Data from a randomized, double-blind, placebo-controlled crossover trial of 12 patients with BTHS were used, including physiological time series data measured using a wearable device (heart rate, respiratory rate, activity, and posture) and functional scores. The latter included the 6-minute walk test (6MWT), Patient-Reported Outcomes Measurement Information System (PROMIS) fatigue score, SWAY Balance Mobile Application score (SWAY balance score), BTHS Symptom Assessment (BTHS-SA) Total Fatigue score, muscle strength by handheld dynamometry, 5 times sit-and-stand test (5XSST), and monolysocardiolipin to cardiolipin ratio (MLCL:CL). Groups were created through median split of the functional scores into "highest score" and "lowest score", and "best response to elamipretide" and "worst response to elamipretide". Agglomerative hierarchical clustering (AHC) models were implemented to assess whether physiological data could classify patients according to functional status and distinguish non-responders from responders to elamipretide. AHC models clustered patients according to their functional status with accuracies of 60–93%, with the greatest accuracies for 6MWT (93%), PROMIS (87%), and SWAY balance score (80%). Another set of AHC models clustered patients with respect to their response to treatment with elamipretide with perfect accuracy (all 100%). Conclusions: In this proof-of-concept study, we demonstrated that continuously acquired physiological measurements from wearable devices can be used to predict functional status and response to treatment among patients with BTHS. [ABSTRACT FROM AUTHOR]

Barth syndrome (BTHS) is a rare genetic disorder caused by pathogenic variants in TAFAZZIN leading to reduced remodeled cardiolipin (CL), a phospholipid essential to mitochondrial function and structure. Cardiomyopathy presents in most patients with BTHS, typically appearing as dilated cardiomyopathy (DCM) in infancy and evolving to hypertrophic cardiomyopathy (HCM) resembling heart failure (HF) with preserved ejection fraction (HFpEF) in some patients ≥12 years. Elamipretide localizes to the inner mitochondrial membrane where it associates with CL, improving mitochondrial function, structure and bioenergetics, including ATP synthesis. Numerous preclinical and clinical studies in BTHS and other forms of HF have demonstrated that elamipretide improves left ventricular relaxation by ameliorating mitochondrial dysfunction, making it well suited for therapeutic use in adolescent and adult patients with BTHS. [ABSTRACT FROM AUTHOR]

Abstract Barth syndrome (BTHS) is an X‐linked disorder characterized by cardiomyopathy, skeletal myopathy, and 3‐methylglutaconic aciduria. The causative pathogenic variants for BTHS are in TAZ, which encodes a putative acyltransferase named tafazzin and is involved in the remodeling of cardiolipin in the inner mitochondrial membranes. Pathogenic variants in TAZ result in mitochondrial structural and functional abnormalities. We report a case of infantile BTHS with severe heart failure, left ventricular noncompaction, and lactic acidosis, having a missense c.640C>T (p.His214Tyr) variant in TAZ, which is considered a pathogenic variant based on the previously reported amino acid substitution at the same site (c.641A>G, p.His214Arg). However, in this previously reported case, heart function was compensated and not entirely similar to the present case. Silico prediction analysis suggested that c.640C>T could alter the TAZ messenger RNA (mRNA) splicing process. TAZ mRNAs in isolated peripheral mononuclear cells from the patient and in vitro splicing analysis using minigenes of TAZ found an 8 bp deletion at the 3′ end of exon 8, which resulted in the formation of a termination codon in the coding region of exon 9 (H214Nfs*3). These findings suggest that splicing abnormalities should always be considered in BTHS.

Barth syndrome (BTHS) is an X-linked mitochondrial disease caused by mutations in the gene encoding for tafazzin (TAZ), a key enzyme in the remodeling of cardiolipin. Mice with a germline deficiency in Taz have been generated (Taz-KO) but not yet fully characterized. We performed physiological assessments of 3-, 6-, and 12-month-old male Taz-KO mice, including measures of perinatal survival, growth, lifespan, gross anatomy, whole-body energy and substrate metabolism, glucose homeostasis, and exercise capacity. Taz-KO mice displayed reduced viability, with lower-than-expected numbers of mice recorded at 4 weeks of age, and a shortened lifespan due to disease progression. At all ages, Taz-KO mice had lower body weights compared with wild-type (Wt) littermates despite similar absolute food intakes. This finding was attributed to reduced adiposity and diminutive organs and tissues, including heart and skeletal muscles. Although there were no differences in basal levels of locomotion between age-matched genotypes, indirect calorimetry studies showed higher energy expenditure measures and respiratory exchange ratios in Taz-KO mice. At the youngest age, Taz-KO mice had comparable glucose tolerance and insulin action to Wt mice, but while these measures indicated metabolic impairments in Wt mice with advancing age that were likely associated with increasing adiposity, Taz-KO mice were protected. Comparisons across the three age-cohorts revealed a significant and more severe deterioration of exercise capacity in Taz-KO mice than in their Wt littermate controls. The Taz-KO mouse model faithfully recapitulates important aspects of BTHS, and thus provides an important new tool to investigate pathophysiological mechanisms and potential therapies. [ABSTRACT FROM AUTHOR]

Barth syndrome (BTHS) is a rare X-linked genetic disease caused by mutations in TAFAZZIN. The tafazzin (Taz) protein is a cardiolipin remodeling enzyme required for maintaining mitochondrial function. Patients with BTHS exhibit impaired mitochondrial respiratory chain and metabolic function and are susceptible to serious infections. B lymphocytes (B cells) play a vital role in humoral immunity required to eradicate circulating antigens from pathogens. Intact mitochondrial respiration is required for proper B-cell function. We investigated whether Taz deficiency in mouse B cells altered their response to activation by anti-cluster of differentiation 40 (anti-CD40) + interleukin-4 (IL-4). B cells were isolated from 3–4-month-old wild type (WT) or tafazzin knockdown (TazKD) mice and were stimulated with anti-CD40 + IL-4 for 24 h and cellular bioenergetics, surface marker expression, proliferation, antibody production, and proteasome and immunoproteasome activities determined. TazKD B cells exhibited reduced mRNA expression of Taz, lowered levels of cardiolipin, and impairment in both oxidative phosphorylation and glycolysis compared to WT B cells. In addition, anti-CD40 + IL-4 stimulated TazKD B cells expressed lower levels of the immunogenic surface markers, cluster of differentiation 86 (CD86) and cluster of differentiation 69 (CD69), exhibited a lower proliferation rate, reduced production of immunoglobulin M and immunoglobulin G, and reduced proteasome and immunoproteasome proteolytic activities compared to WT B cells stimulated with anti-CD40 + IL-4. The results indicate that Taz is required to support T-cell-dependent signaling activation of mouse B cells. [ABSTRACT FROM AUTHOR]

Abstract Cardiomyopathy is the most common presenting feature of Barth syndrome, often presenting in infancy with severe heart failure and cardiac dysfunction. Historically, affected infants commonly died early after presentation, sometimes before a diagnosis of Barth syndrome was made. With increases in awareness of Barth syndrome and in the care of infants with severe heart failure, survival of children with Barth syndrome and severe heart failure has improved. We describe our experience caring for five unrelated boys with Barth syndrome who presented with severe cardiomyopathy and heart failure prior to age 2 who have had marked improvement with long‐term response to medical heart failure therapy.

A mood-stabilizing anticonvulsant valproic acid (VPA) is a drug with a pleiotropic effect on cells. Here, we describe the impact of VPA on the metabolic function of human HAP1 cells. We show that VPA altered the biosynthetic pathway of cardiolipin (CL) and affected the activities of mitochondrial enzymes such as pyruvate dehydrogenase, α-ketoglutarate dehydrogenase and NADH dehydrogenase. We demonstrate that a therapeutic dose of VPA (0.6 mM) has a harmful effect on cell growth and increases the production of reactive oxygen species and superoxides. On the contrary, less concentrated VPA (0.06 mM) increased the activities of CL-dependent enzymes leading to an increased level of oxidative phosphorylation and ATP production. The effect of VPA was also tested on the Barth syndrome model, which is characterized by a reduced amount of CL and an increased level of monolyso-CL. In this model, VPA treatment slightly attenuated the mitochondrial defects by altering the activities of CL-dependent enzymes. However, the presence of CL was essential for the increase in ATP production by VPA. Our findings highlight the potential therapeutic role of VPA in normalizing mitochondrial function in BTHS and shed light on the intricate interplay between lipid metabolism and mitochondrial physiology in health and disease. This study investigates the dose-dependent effect of valproate, a mood-stabilizing drug, on mitochondrial function. The therapeutic concentration reduced overall cellular metabolic activity, while a subtherapeutic concentration notably improved the function of cardiolipin-dependent proteins within mitochondria. These findings shed light on novel aspects of valproate's effect and suggest potential practical applications for its use. By elucidating the differential effects of valproate doses on mitochondrial activity, this research underscores the drug's multifaceted role in cellular metabolism and highlights avenues for further exploration in therapeutic interventions. [Display omitted] • The TAFFAZIN mutation causes multiple lipid changes. • The effect of valproic acid on cellular metabolism is dose-dependent. • Valproic acid alters mitochondrial enzyme activities. • Cardiolipin plays an important role in the molecular mechanism of valproic acid. [ABSTRACT FROM AUTHOR]

Barth syndrome (BTHS) is caused by mutations in tafazzin resulting in deficits in cardiolipin remodeling that alter major metabolic processes. The tafazzin gene is encoded on the X chromosome, and therefore BTHS primarily affects males. Female carriers are typically considered asymptomatic, but age-related changes have been reported in female carriers of other X-linked disorders. Therefore, we examined the phenotype of female mice heterozygous for deletion of the tafazzin gene (Taz-HET) at 3 and 12 months of age. Food intakes, body masses, lean tissue and adipose depot weights, daily activity levels, metabolic measures, and exercise capacity were assessed. Age-related changes in mice resulted in small but significant genotype-specific differences in Taz-HET mice compared with their female Wt littermates. By 12 months, Taz-HET mice weighed less than Wt controls and had smaller gonadal, retroperitoneal, and brown adipose depots and liver and brain masses, despite similar food consumption. Daily movement, respiratory exchange ratio, and total energy expenditure did not vary significantly between the age-matched genotypes. Taz-HET mice displayed improved glucose tolerance and insulin sensitivity at 12 months compared with their Wt littermates but had evidence of slightly reduced exercise capacity. Tafazzin mRNA levels were significantly reduced in the cardiac muscle of 12-month-old Taz-HET mice, which was associated with minor but significant alterations in the heart cardiolipin profile. This work is the first to report the characterization of a model of female carriers of heterozygous tafazzin deficiency and suggests that additional study, particularly with advancing age, is warranted.

The extracellular matrix (ECM) provides both physical and chemical cues that dictate cell function and contribute to muscle maintenance. Muscle cells require efficient mitochondria to satisfy their high energy demand, however, the role the ECM plays in moderating mitochondrial function is not clear. We hypothesized that the ECM produced by stromal cells with mitochondrial dysfunction (Barth syndrome, BTHS) provides cues that contribute to metabolic dysfunction independent of muscle cell health. To test this, we harnessed the ECM production capabilities of human pluripotent stem-cell-derived cardiac fibroblasts (hPSC-CFs) from healthy and BTHS patients to fabricate cell-derived matrices (CDMs) with controlled topography, though we found that matrix composition from healthy versus diseased cells influenced myotube formation independent of alignment cues. To further investigate the effects of matrix composition, we then examined the influence of healthy- and BTHS-derived CDMs on myotube formation and metabolic function. We found that BTHS CDMs induced lower fusion index, lower ATP production, lower mitochondrial membrane potential, and higher ROS generation than the healthy CDMs. These findings imply that BTHS-derived ECM alone contributes to myocyte dysfunction in otherwise healthy cells. Finally, to investigate potential mechanisms, we defined the composition of CDMs produced by hPSC-CFs from healthy and BTHS patients using mass spectrometry and identified 15 ECM and related proteins that were differentially expressed in the BTHS-CDM compared to healthy CDM. Our results highlight that ECM composition affects skeletal muscle formation and metabolic efficiency in otherwise healthy cells, and our methods to generate patient-specific CDMs are a useful tool to investigate the influence of the ECM on disease progression and to investigate variability among diseased patients. Muscle function requires both efficient metabolism to generate force and structured extracellular matrix (ECM) to transmit force, and we sought to examine the interactions between metabolism and ECM when metabolic disease is present. We fabricated patient-specific cell derived matrices (CDMs) with controlled topographic features to replicate the composition of healthy and mitochondrial-diseased (Barth syndrome) ECM. We found that disease-derived ECM negatively affects metabolic function of otherwise healthy myoblasts, and we identified several proteins in disease-derived ECM that may be mediating this dysfunction. We anticipate that our patient-specific CDM system could be fabricated with other topographies and cell types to study cell functions and diseases of interest beyond mitochondrial dysfunction and, eventually, be applied toward personalized medicine. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: Natural history studies are increasingly recognized as having an important role in drug development for rare diseases. A phase 3, observational, retrospective, and non-interventional study was designed to establish a natural history control (NHC) cohort of patients with Barth syndrome (BTHS) to provide further analysis of the efficacy of elamipretide observed in an open-label extension (OLE) phase of the TAZPOWER trial, a clinical trial that tested the efficacy of 40 mg daily of elamipretide in patients with BTHS.Methods: This was a retrospective, non-interventional study. A propensity score model was used to compare elamipretide-treated patients and NHCs. The analysis included 8 patients from the TAZPOWER OLE and 19 untreated NHCs (including 12 with serial echocardiographic assessments).Results: For the 6-min walk test (6MWT, primary endpoint), the least squares (LS) mean difference between groups was 79.7 m (P = 0.0004) at week 64 and 91.0 m (P = 0.0005) at week 76 in favor of elamipretide. Significant improvements in muscle strength (secondary endpoint), as assessed by handheld dynamometry (HHD) were also observed with elamipretide, with LS mean differences of 40.8 Newtons at 64 weeks (P = 0.0002) and 56.7 Newtons at 76 weeks (P = 0.0005). Patients continuously treated with elamipretide also experienced statistically significant improvements in other secondary endpoints (i.e., 5 times sit-to-stand [5XSST], multi-domain responder index [MDRI]). The functional improvements were robust to sensitivity analyses. Left ventricular stroke volume increased from baseline in patients with elamipretide but decreased in NHCs.Conclusions: Overall, the study established a NHC for use in assessing the efficacy of therapeutic interventions in patients with BTHS and the results suggest that elamipretide may improve natural history of BTHS at least in part by attenuating the natural decline in heart function and provide meaningful improvements in heart function and functional capacity in patients with BTHS compared to NHCs.Highlights: A matched Natural History Control (NHC) was used to evaluate elamipretide in BTHS Elamipretide may improve natural history of BTHS by attenuating natural decline in heart function Elamipretide was associated with meaningful clinical improvements in skeletal muscle and cardiovascular parameters that were not observed in NHCs The study established a NHC for use in assessing the efficacy of therapeutic interventions in BTHS. [ABSTRACT FROM AUTHOR]

Barth syndrome is a rare and potentially fatal X-linked disease characterized by cardiomyopathy, skeletal muscle weakness, growth delays, and cyclic neutropenia. Patients with Barth syndrome are prone to high risk of mortality in infancy and the development of cardiomyopathy with severe weakening of the immune system. Elamipretide is a water-soluble, aromatic-cationic, mitochondria-targeting tetrapeptide that readily penetrates and transiently localizes to the inner mitochondrial membrane. Therapy with elamipretide facilitates cell health by improving energy production and inhibiting excessive formation of reactive oxygen species, thus alleviating oxidative stress. Elamipretide crosses the outer membrane of the mitochondrion and becomes associated with cardiolipin, a constituent phospholipid of the inner membrane. Elamipretide improves mitochondrial bioenergetics and morphology rapidly in induced pluripotent stem cells from patients with Barth syndrome and other genetically related diseases characterized by pediatric cardiomyopathy. Data with elamipretide across multiple models of disease are especially promising, with results from several studies supporting the use of elamipretide as potential therapy for patients with Barth syndrome, particularly where there is a confirmed diagnosis of cardiomyopathy. This review highlights the challenges and opportunities presented in treating Barth syndrome cardiomyopathy patients with elamipretide and addresses evidence supporting the durability of effect of elamipretide as a therapeutic agent for Barth syndrome, especially its likely durable effects on progression of cardiomyopathy following the cessation of drug treatment and the capability of elamipretide to structurally reverse remodel the failing left ventricle at the global, cellular, and molecular level in a gradual manner through specific targeting of the mitochondrial inner membrane. [ABSTRACT FROM AUTHOR]

Barth syndrome (BTHS) is a rare mitochondrial disease caused by pathogenic variants in the gene TAFAZZIN, which leads to abnormal cardiolipin (CL) metabolism on the inner mitochondrial membrane. Although TAFAZZIN is ubiquitously expressed, BTHS involves a complex combination of tissue specific phenotypes including cardiomyopathy, neutropenia, skeletal myopathy, and growth delays, with a relatively minimal neurological burden. To understand both the developmental and functional effects of TAZ-deficiency in different tissues, we generated isogenic TAZ knockout (TAZ-KO) and WT cardiomyocytes (CMs) and neural progenitor cells (NPCs) from CRISPR-edited induced pluripotent stem cells (iPSCs). In TAZ-KO CMs we discovered evidence of dysregulated mitophagy including dysmorphic mitochondria and mitochondrial cristae, differential expression of key autophagy-associated genes, and an inability of TAZ-deficient CMs to properly initiate stress-induced mitophagy. In TAZ-deficient NPCs we identified novel phenotypes including a reduction in CIV abundance and CIV activity in the CIII2&CIV2 intermediate complex. Interestingly, while CL acyl chain manipulation was unable to alter mitophagy defects in TAZ-KO CMs, we found that linoleic acid or oleic acid supplementation was able to partially restore CIV abundance in TAZ-deficient NPCs. Taken together, our results have implications for understanding the tissue-specific pathology of BTHS and potential for tissue-specific therapeutic targeting. Moreover, our results highlight an emerging role for mitophagy in the cardiac pathophysiology of BTHS and reveal a potential neuron-specific bioenergetic phenotype., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Fibroblast-ECM (dys)regulation is associated with a plethora of diseases. The ECM acts as a reservoir of inflammatory factors and cytokines that mediate molecular mechanisms within cardiac cell populations. The role of ECM-mitochondria crosstalk in the development and progression of cardiac disorders remains uncertain. We evaluated the influence of ECM produced by stromal cells from patients with the mitochondrial cardiomyopathy (Barth syndrome, BTHS) and unaffected healthy controls on cardiac fibroblast (CF) metabolic function. To do this, cell-derived matrices CDMs were generated from BTHS and healthy human pluripotent stem cell-derived CFs (hPSC-CF) and used as cell culture substrates. BTHS CDMs negatively impacted the mitochondrial function of healthy hPSC-CFs while healthy CDMs improved mitochondrial function in BTHS hPSC-CFs. Mass spectrometry comparisons identified 5 matrisome proteins differentially expressed in BTHS compared to healthy CDM. Our results highlight a key role for the ECM in disease through its impact on mitochondrial function., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Barth syndrome is a rare genetic disease caused by abnormal cardiolipin metabolism, characterized by high mortality within 5 years of diagnosis due to heart failure and/or infectious complications. This article describes a clinical case of an adult patient with Barth syndrome. The peculiarities of the course of the disease are described, including the transformation of the hypertrophic type of cardiomyopathy into the hypokinetic type as the patient grew older. This article demonstrates the difficulty in selecting the optimal treatment of a patient with Barth syndrome in real clinical practice, in the absence of clearly prescribed recommendations and pathogenetic therapy.

Barth syndrome (BTHS) is a rare X-linked recessive genetic disorder characterized by a broad spectrum of clinical features including cardiomyopathy, skeletal myopathy, neutropenia, growth delay, and 3-methylglutaconic aciduria. This disease is caused by loss-of-function mutations in the TAFAZZIN gene located on chromosome Xq28, resulting in cardiolipin deficiency. Most patients are diagnosed in childhood, and the mortality rate is highest in the early years. We report a case of acute, life-threatening metabolic decompensation occurring one day after birth. A novel TAFAZZIN splice site mutation was identified in the patient, marking the first reported case of such a mutation in BTHS identified in China. The report aims to expand our understanding of the spectrum of TAFAZZIN mutations in BTHS., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2024 Che, Li, Jia, Liu, Hu, Zhang and Liu.)

Abstract Background Barth syndrome (BS) is a life-threatening genetic disease caused by abnormal lipids in the mitochondria of cells and mostly affects young males. Those living with BS have severe exercise intolerance, lethargy and fatigue due to muscle disease which affect their daily life. Previous research suggests a need for qualitative exploration of self-regulation in BS and the inter-personal processes at play in family life. Therefore this study aimed to explore self-regulation and coping strategies and inter-personal responses in individuals and families affected by Barth syndrome. A multi-perspective qualitative study based on face to face, semi-structured, in-depth interviews with 11 participants (9–27 years, mean 15 years) with BS and/or their parents participating in a randomised double-blind clinical drug trial (CARDIOMAN). Interviews were transcribed verbatim and managed in NVivo prior to conducting a thematic analysis (AS and GH). Results Four key themes were identified: diagnosis and treatment, social support, identity and social integration, symptoms and self-regulation. The present findings suggest that self-regulation and coping in boys with BS was interpersonal and contingent on parental awareness such that parents were aware that their child had a limited energy reserve and that had to be managed due to the implications of fatigue for daily living. Conclusion The findings support previous quantitative work demonstrating that children and parents tend to share a coherent view of BS. However, there is a need for greater awareness from others within the wider context of social and employment networks to minimise adverse implications for future life choices.