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Purpose of Review: This review highlights the current lack of disease specific therapies available for arrhythmogenic cardiomyopathy (ACM) and explores recent new advances toward novel genotype specific therapies. Recent Findings: Although our understanding of ACM genetics has grown, current therapies are largely based on the general treatment strategies of arrhythmias and heart failure that do not target the diverse underlying pathogenic causes of ACM. Recently, there have been several efforts toward genotype-specific targeted therapies including a small molecule inhibitor for LMNA cardiomyopathy, three distinct gene replacement therapy approaches for PKP2 cardiomyopathy, as well as early work with base editing and prime editing on RBM20 cardiomyopathy. Summary: There is currently a lack of ACM-specific therapies with minimal disease modifying treatments. Advances in gene replacement and editing offer hope for promising novel genotype-specific therapies with the goal of reversing the underlying disease process. [ABSTRACT FROM AUTHOR]

Familial cardiomyopathy is a precursor of heart failure and sudden cardiac death. Over the past several decades, researchers have discovered numerous gene mutations primarily in sarcomeric and cytoskeletal proteins causing two different disease phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathies. However, molecular mechanisms linking genotype to phenotype remain unclear. Here, we employ a systems approach by integrating experimental findings from preclinical studies (e.g., murine data) into a cohesive signaling network to scrutinize genotype to phenotype mechanisms. We developed an HCM/DCM signaling network model utilizing a logic-based differential equations approach and evaluated model performance in predicting experimental data from four contexts (HCM, DCM, pressure overload, and volume overload). The model has an overall prediction accuracy of 83.8%, with higher accuracy in the HCM context (90%) than DCM (75%). Global sensitivity analysis identifies key signaling reactions, with calcium-mediated myofilament force development and calcium-calmodulin kinase signaling ranking the highest. A structural revision analysis indicates potential missing interactions that primarily control calcium regulatory proteins, increasing model prediction accuracy. Combination pharmacotherapy analysis suggests that downregulation of signaling components such as calcium, titin and its associated proteins, growth factor receptors, ERK1/2, and PI3K-AKT could inhibit myocyte growth in HCM. In experiments with patient-specific iPSC-derived cardiomyocytes (MLP-W4R;MYH7-R723C iPSC-CMs), combined inhibition of ERK1/2 and PI3K-AKT rescued the HCM phenotype, as predicted by the model. In DCM, PI3K-AKT-NFAT downregulation combined with upregulation of Ras/ERK1/2 or titin or Gq protein could ameliorate cardiomyocyte morphology. The model results suggest that HCM mutations that increase active force through elevated calcium sensitivity could increase ERK activity and decrease eccentricity through parallel growth factors, Gq-mediated, and titin pathways. Moreover, the model simulated the influence of existing medications on cardiac growth in HCM and DCM contexts. This HCM/DCM signaling model demonstrates utility in investigating genotype to phenotype mechanisms in familial cardiomyopathy.

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.

Base editors are emerging as powerful tools to correct single‐nucleotide variants and treat genetic diseases. In particular, the adenine base editors (ABEs) exhibit robust and accurate adenine‐to‐guanidine editing capacity and have entered the clinical stage for cardiovascular therapy. Despite the tremendous progress using ABEs to treat heart diseases, a standard technical route toward successful ABE‐based therapy remains to be fully established. In this study, we harnessed adeno‐associated virus (AAV) and a mouse model carrying the cardiomyopathy‐causing Lmna c.1621C > T mutation to demonstrate key steps and concerns in designing a cardiac ABE experiment in vivo. We found DeepABE as a reliable deep‐learning‐based model to predict ABE editing outcomes in the heart. Screening of sgRNAs for a Cas9 mutant with relieved protospacer adjacent motif (PAM) allowed the reduction of bystander editing. The ABE editing efficiency can be significantly enhanced by modifying the TadA and Cas9 variants, which are core components of ABEs. The ABE systems can be delivered into the heart via either dual AAV or all‐in‐one AAV vectors. Together, this study showcased crucial technical considerations in designing an ABE system for the heart and pointed out major challenges in further improvement of this new technology for gene therapy. [ABSTRACT FROM AUTHOR]

Purpose of Review: Preimplantation genetic testing for monogenic conditions (PGT-M) is an increasingly utilized reproductive technology for patients with inherited heart disease (IHD). In this article, we provide an overview of the PGT-M process, including current guidance about its use, and review recent data about the perspectives and experiences of patients considering the use of PGT-M. Recent Findings: PGT-M is used for a variety of IHDs; however, there is evidence that providers do not consistently raise this topic with patients, which may be due to a lack of knowledge about PGT-M. Regardless of the condition, patients report similar motivations for using PGT-M, such as the desire for a healthy child and the wish to save offspring from suffering. Patients make individualized decisions that are influenced by their lived experience with the diagnosis, a sense of responsibility to prevent disease transmission and other personal and logistical considerations. The PGT-M process can be challenging and each patient requires comprehensive information and support throughout. Summary: PGT-M is a complex multi-step process whereby individual decision-making is influenced by various intrinsic and extrinsic factors. Adequate information and support are necessary for individual decision-making and expectation-setting. This is best accomplished by a multidisciplinary collaboration including cardiology, genetics, reproductive endocrinologists, and obstetric providers. [ABSTRACT FROM AUTHOR]

We present two female patients with recurrent episodes of myocardial injury, consisting of acute chest pain and elevated cardiac markers without coronary artery disease. Cardiovascular magnetic resonance imaging identified extensive late gadolinium enhancement suggestive of an inherited cardiomyopathy. Genetic testing showed heterozygous pathogenic variants in the desmoplakin (DSP) gene, the gene coding for the desmoplakin protein, a structural protein found in the cardiac desmosome. Pathogenic variants in the DSP gene are associated with dilated and arrhythmogenic cardiomyopathy. DSP cardiomyopathies may cause recurring myocardial injury mimicking an acute coronary syndrome or myocarditis. Cardiac magnetic resonance imaging is key in its diagnosis due to its specifying imaging features. Genetic testing is essential for the evaluation and confirmation of the diagnosis. [ABSTRACT FROM AUTHOR]

Cardiovascular disease (CVD) during pregnancy varies significantly worldwide, influenced by factors such as access to healthcare, delayed diagnosis, causes, and risk factors. Our study sought to explore the spectrum of CVD present in pregnant women in the United Arab Emirates to better understand this population's unique needs and challenges. Central to our study is an emphasis on the importance of implementing a multidisciplinary approach that involves the collaboration of obstetricians, cardiologists, geneticists, and other healthcare professionals to ensure that patients receive comprehensive and coordinated care. This approach can also help identify high-risk patients and implement preventive measures to reduce the occurrence of adverse maternal outcomes. Furthermore, increasing awareness among women about the risk of CVD during pregnancy and obtaining detailed family histories can help in the early identification and management of these conditions. Genetic testing and family screening can also aid in identifying inherited CVD that can be passed down through families. To illustrate the significance of such an approach, we provide a comprehensive analysis of five women's cases from our retrospective study of 800 women. The findings from our study emphasize the importance of addressing maternal cardiac health in pregnancy and the need for targeted interventions and improvements in the existing healthcare system to reduce adverse maternal outcomes. [ABSTRACT FROM AUTHOR]

Background: Genetic findings influence clinical care of patients suspected of hereditary cardiac diseases. As additional knowledge arises over time, the classification of genetic variants may change. The labor cost associated with systematic manual reevaluation for reported variants is substantial. We applied an automated variant classifier for reevaluation of previous reported variants to assess how such tools may assist in manual reevaluation., Methods: Historically (2010-2022), patients (N = 2987) suspected of inherited cardiomyopathies or ion-channel disorders were screened for genetic variants in at least one of up to 114 genes. We had reported 1455 unique variants, of which 742 were among the 14 most relevant genes. In the 14-gene-group, we compared our reported classification to that of an autoclassifier and manually reevaluated variant classification of all variants. Among the remaining genes (N = 100), only variants where the autoclassifier predicted change of clinical impact, such as variant of uncertain significance to likely pathogenic or oppositely, were manually reevaluated., Results: We identified 9% (66/742) of variants with clinical impact in the 14-gene-group. Of these, 91% could have been identified solely evaluating the 120 variants where the autoclassifier had predicted a change of clinical impact. In the 100 remaining genes, a change of clinical impact was identified in 3% (22/713) after manual reevaluation., Conclusion: Using an autoclassifier reduces the workload to identify variants likely to have a change in variant class with clinical impact. Hence, we recommend using such tools to identify the variants most relevant to manually reevaluate to improve patient care., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Genetic variants in α-actinin-2 (ACTN2) are associated with several forms of (cardio)myopathy. We previously reported a heterozygous missense (c.740C>T) ACTN2 gene variant, associated with hypertrophic cardiomyopathy, and characterized by an electro-mechanical phenotype in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Here, we created with CRISPR/Cas9 genetic tools two heterozygous functional knock-out hiPSC lines with a second wild-type (ACTN2wt) and missense ACTN2 (ACTN2mut) allele, respectively. We evaluated their impact on cardiomyocyte structure and function, using a combination of different technologies, including immunofluorescence and live cell imaging, RNA-seq, and mass spectrometry. This study showed that ACTN2mut presents a higher percentage of multinucleation, protein aggregation, hypertrophy, myofibrillar disarray, and activation of both the ubiquitin-proteasome system and the autophagy-lysosomal pathway as compared to ACTN2wt in 2D-cultured hiPSC-CMs. Furthermore, the expression of ACTN2mut was associated with a marked reduction of sarcomere-associated protein levels in 2D-cultured hiPSC-CMs and force impairment in engineered heart tissues. In conclusion, our study highlights the activation of proteolytic systems in ACTN2mut hiPSC-CMs likely to cope with ACTN2 aggregation and therefore directs towards proteopathy as an additional cellular pathology caused by this ACTN2 variant, which may contribute to human ACTN2-associated cardiomyopathies. [ABSTRACT FROM AUTHOR]

Purpose of Review: The disease burden of inherited dilated cardiomyopathy (DCM) is large and likely underestimated. This population stands to benefit immensely from therapeutic approaches tailored to the underlying genetic causes. Here, we review recent advances in understanding novel genotype–phenotype relationships and how these can improve the care of patients with inherited DCM. Recent Findings: In the last several years, discovery of novel DCM-associated genes, gene-specific DCM outcomes, and nuanced information about variant-environment interactions have advanced our understanding of inherited DCM. Specifically, novel associations of genes with specific clinical phenotypes can help to assess sudden cardiac death risk and guide counseling around behavioral and environmental exposures that may worsen disease. Summary: Important expansions of the current genotype-phenotype profiling include the newly DCM-associated FLNC variant, prognostically significant LMNA, DSP inflammatory cardiomyopathy, and the highly penetrant features of RBM20 variants as well as the role of TTN variants in compounding the effects of environmental factors on toxin-mediated DCM. Future directions to improve diagnostic accuracy and prognostic improvement in DCM will center not just on identification of new genes, but also on understanding the interaction of known and novel variants in known DCM genes with patient genetic background and environment. [ABSTRACT FROM AUTHOR]

Background Inherited cardiomyopathies (ICs) are relatively rare. General cardiologists have little experience in diagnosing and managing these conditions. International societies have recognized the need for dedicated IC clinics. However, only few reports on such clinics are available. Methods and Results Clinical data of patients referred to our clinic during its first 2 years for a personal or family history of (possible) IC were analyzed. A total of 207 patients from 196 families were seen; 13% of probands had their diagnosis changed. Diagnosis was most commonly altered in patients referred for possible arrhythmogenic dominant right ventricular cardiomyopathy (62.5%). A total of 90% of probands had genetic testing, of whom 27.3% harbored a likely pathogenic or pathogenic variant. Of patients with confirmed hypertrophic cardiomyopathy, 31 (28.7%) were treated for left ventricular outflow tract obstruction, including septal reduction in 13. Patients with either hypertrophic cardiomyopathy or left ventricular noncompaction and a history of atrial fibrillation were started on oral anticoagulation. Oral anticoagulation was also discussed with all patients with hypertrophic cardiomyopathy and apical aneurysm. Patients with a definite diagnosis of arrhythmogenic dominant right ventricular cardiomyopathy were started on β‐blockers and given restrictive exercise prescriptions. A total of 17 patients with hypertrophic cardiomyopathy and 5 patients with likely pathogenic or likely variants in arrhythmogenic genes received primary prevention implantable cardioverter‐defibrillators. No implantable cardioverter‐defibrillators were warranted for arrhythmogenic dominant right ventricular cardiomyopathy. A total of 76 family members from 24 families had cascade screening, 32 of whom carried the familial variant. A total of 21 members from 13 gene‐elusive families were evaluated by clinical screening, 3 of whom had positive screening. Conclusions Specialized IC clinics may improve diagnosis, management, and outcomes of patients with (possible) IC and their family members.

Abstract Background Identifying disease-causing genetic variants in a particular population improves the molecular diagnosis of genetic disorders. National genome databases provide valuable information on this matter. This study aimed to investigate the genomic variants of the MYH7 gene, related to the common heart disease, i.e., hereditary cardiomyopathy. Results MYH7 gene variants were extracted from the Iranome database and loaded into SPSS software. The filtration steps were performed based on the variant specification and with emphasis on identifying missense changes. Using predictive algorithms, different aspects of the changes such as allele frequency and functional defects were investigated. Our results showed that 41 (17.4%) coding variants were synonymous compared with 18 (7.7%) missense alterations. The missense variants were mostly observed in exons 20–40 that encode MyHC α-helical rod tail. The p.Pro211Leu, p.Arg787His, p.Val964Leu, p.Arg1277Gln, and p.Ala1603Thr were already known to be associated with inherited cardiomyopathy. Four of the missense variants, p.Asn1623Ser, p.Arg1588His, p.Phe1498Tyr, and p.Arg1129Ser, were located on MyHC α-helical rod tail and none of them was annotated on dbSNP or genomAD databases. Conclusion Our study showed several MYH7 variants associated with the disease in the Iranian population. The results emphasize the importance of analyzing the exons encoding MyHC α-helical rod tail. The investigation of genomic databases can be considered as a cost-effective strategy using targeted mutation detection analyses. The efficacy of this prediction method should be elucidated in further studies on patients’ cohorts.

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Genetic variants in α-actinin-2 (ACTN2) are associated with several forms of (cardio)myopathy. We previously reported a heterozygous missense (c.740C>T) ACTN2 gene variant, associated with hypertrophic cardiomyopathy, and characterized by an electro-mechanical phenotype in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Here, we created with CRISPR/Cas9 genetic tools two heterozygous functional knock-out hiPSC lines with a second wild-type (ACTN2wt) and missense ACTN2 (ACTN2mut) allele, respectively. We evaluated their impact on cardiomyocyte structure and function, using a combination of different technologies, including immunofluorescence and live cell imaging, RNA-seq, and mass spectrometry. This study showed that ACTN2mut presents a higher percentage of multinucleation, protein aggregation, hypertrophy, myofibrillar disarray, and activation of both the ubiquitin-proteasome system and the autophagy-lysosomal pathway as compared to ACTN2wt in 2D-cultured hiPSC-CMs. Furthermore, the expression of ACTN2mut was associated with a marked reduction of sarcomere-associated protein levels in 2D-cultured hiPSC-CMs and force impairment in engineered heart tissues. In conclusion, our study highlights the activation of proteolytic systems in ACTN2mut hiPSC-CMs likely to cope with ACTN2 aggregation and therefore directs towards proteopathy as an additional cellular pathology caused by this ACTN2 variant, which may contribute to human ACTN2-associated cardiomyopathies.

In the past decades, researchers discovered the contribution of genetic defects to the pathogenesis of primary cardiomyopathy and tried to explain the pathogenesis of these diseases by establishing a variety of disease models. Although human heart tissues and primary cardiomyocytes have advantages in modeling human heart diseases, they are difficult to obtain and culture in vitro. Defects developed in genetically modified animal models are notably different from human diseases at the molecular level. The advent of human induced pluripotent stem cells (hiPSCs) provides an unprecedented opportunity to further investigate the pathogenic mechanisms of inherited cardiomyopathies in vitro using patient-specific hiPSC-derived cardiomyocytes. In this review, we will make a summary of recent advances in in vitro inherited cardiomyopathy modeling using hiPSCs.

Abstract Background Cardiomyopathies are the most common clinical and genetic heterogeneity cardiac diseases, and genetic contribution in particular plays a major role in patients with primary cardiomyopathies. The aim of this study is to investigate cases of inherited cardiomyopathy (IC) for potential disease-causing mutations in 64 genes reported to be associated with IC. Methods A total of 110 independent cases or families diagnosed with various primary cardiomyopathies, including hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, left ventricular non-compaction, and undefined cardiomyopathy, were collected after informed consent. A custom designed panel, including 64 genes, was screened using next generation sequencing on the Ion Torrent PGM platform. The best candidate disease-causing variants were verified by Sanger sequencing. Results A total of 78 variants in 73 patients were identified. After excluding the variants predicted to be benign and VUS, 26 pathogenic or likely pathogenic variants were verified in 26 probands (23.6%), including a homozygous variant in the SLC25A4 gene. Of these variants, 15 have been reported in the Human Gene Mutation Database or ClinVar database, while 11 are novel. The majority of variants were observed in the MYH7 (8/26) and MYBPC3 (6/26) gene. Titin (TTN) truncating mutations account for 13% in our dilated cardiomyopathy cases (3/23). Conclusions This study provides an overview of the genetic aberrations in this cohort of Chinese IC patients and demonstrates the power of next generation sequencing in IC. Genetic results can provide precise clinical diagnosis and guidance regarding medical care for some individuals.

Background: Identifying disease-causing genetic variants in a particular population improves the molecular diagnosis of genetic disorders. National genome databases provide valuable information on this matter. This study aimed to investigate the genomic variants of the MYH7 gene, related to the common heart disease, i.e., hereditary cardiomyopathy. Results: MYH7 gene variants were extracted from the Iranome database and loaded into SPSS software. The filtration steps were performed based on the variant specification and with emphasis on identifying missense changes. Using predictive algorithms, different aspects of the changes such as allele frequency and functional defects were investigated. Our results showed that 41 (17.4%) coding variants were synonymous compared with 18 (7.7%) missense alterations. The missense variants were mostly observed in exons 20–40 that encode MyHC α-helical rod tail. The p.Pro211Leu, p.Arg787His, p.Val964Leu, p.Arg1277Gln, and p.Ala1603Thr were already known to be associated with inherited cardiomyopathy. Four of the missense variants, p.Asn1623Ser, p.Arg1588His, p.Phe1498Tyr, and p.Arg1129Ser, were located on MyHC α-helical rod tail and none of them was annotated on dbSNP or genomAD databases. Conclusion: Our study showed several MYH7 variants associated with the disease in the Iranian population. The results emphasize the importance of analyzing the exons encoding MyHC α-helical rod tail. The investigation of genomic databases can be considered as a cost-effective strategy using targeted mutation detection analyses. The efficacy of this prediction method should be elucidated in further studies on patients' cohorts. [ABSTRACT FROM AUTHOR]

Background: The prevalence and clinical course of atrial fibrillation (AF) in hypertrophic cardiomyopathy (HCM) is well described, though less so for other inherited cardiomyopathies (familial dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, left ventricular noncompaction); and inherited arrhythmia syndromes (long QT syndrome, Brugada syndrome or catecholaminergic polymorphic ventricular tachycardia [CPVT]). We examined the frequency, clinical characteristics and AF‐related management and outcomes amongst this patient population. Methods: We retrospectively studied consecutive probands with inherited cardiomyopathy (n = 962) and inherited arrhythmia syndromes (n = 195) evaluated between 2002 and 2018. Results: AF was observed in 5% to 31% of patients, with the highest frequency in HCM. Age of AF onset was 45.8 ± 21.9 years in the inherited arrhythmia syndromes compared with 53.3 ± 15.3 years in the inherited cardiomyopathies, with four CPVT patients developing AF at a median age of 20 years. Overall, 11% of patients with AF had a transient ischemic attack or stroke of which a total of 80% were anticoagulated; with 48% of events occurring at a CHA2DS2‐VASc < 2. Amongst sarcomere‐positive HCM, AF was independently associated with age (odds ratio [OR], 1.05; 95% confidence interval [CI], 1.02‐1.08; P =.0014), left atrial area (OR, 1.11; 95% CI, 1.05‐1.17; P =.0005) and MYH7 variants (OR, 2.55; 95% CI, 1.16‐5.61; P =.020). Conclusion: Up to one‐third of inherited heart disease patients will develop AF. While common general population risk factors are key in patients with HCM, the genotype is independently associated with AF. Amongst inherited arrhythmia syndromes, AF is less common, though often occurs below the age of 50 years. [ABSTRACT FROM AUTHOR]

Advances in the field of human genetics have led to an accumulating understanding of the genetic basis of distinct nonischemic cardiomyopathies associated with ventricular tachycardias (VTs) and sudden cardiac death. To date, there is an increasing proportion of patients with inherited cardiomyopathies requiring catheter ablation for VTs. This review provides an overview of disease-causing gene mutations frequently encountered and relevant for clinical electrophysiologists. Available data on VT ablation in patients with an inherited etiology and a phenotype of a nondilated left ventricular cardiomyopathy, dilated cardiomyopathy, or hypertrophic cardiomyopathy are summarized. VTs amenable to catheter ablation are related to nonischemic fibrosis. Recent insights into genotype-phenotype relations of subtype and location of fibrosis have important implications for treatment planning. Current strategies to delineate nonischemic fibrosis and related arrhythmogenic substrates using multimodal imaging, image integration, and electroanatomical mapping are provided. The ablation approach depends on substrate location and extension. Related procedural aspects including patient-tailored (enhanced) ablation strategies and outcomes are outlined. Challenging substrates for VT and the underlying inherited etiologies with a high risk for rapid progressive heart failure contribute to poor outcomes after catheter ablation. Electroanatomical data obtained during ablation may allow the identification of patients at particular risk who need to be considered for early work-up for left ventricular assist device implantation or heart transplantation., Competing Interests: Funding Support and Author Disclosures The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Cardiac involvement in myotonic dystrophy type 1 (MD1) includes conduction disease, arrhythmias, and left-ventricular (LV) systolic dysfunction leading to an increased sudden cardiac death risk. An understanding of the interplay between electrical and structural myocardial changes could improve the prediction of adverse cardiac events. We aimed to explore the relationship between signs of cardiomyopathy by conventional and advanced cardiovascular magnetic resonance (CMR), and electrical abnormalities in MD1. Methods: Fifty-seven MD1 patients (43 ± 13 years, 46% male) and 15 matched controls (41 ± 7 years, 53% male) underwent CMR including cine-imaging with feature-tracking strain analysis, late gadolinium enhancement (LGE), and native/post-contrast T1-mapping with extracellular volume calculation. Standard 12-lead and long-term ECG monitoring were performed as screening for rhythm and/or conduction abnormalities. Results: Abnormal ECGs were recorded in 40% of MD1; a pathologic CMR was found in 44%: 21% had an impaired LV–EF and 32% showed non-ischemic LGE. When looking at MD1 patients with available long-term ECG monitoring (n = 39), those with atrial fibrillation (Afib)/flutter(Afl) episodes had lower LV–EF (52 ± 7 vs. 60 ± 5%, p = 0.002), lower global longitudinal strain (− 17 ± 3 vs. − 20 ± 3%, p = 0.034), a trend to lower left atrial emptying fraction (LA–EF) (44 ± 14 vs. 55 ± 8%, p = 0.08), and higher prevalence of LGE (88% vs. 23%, p = 0.001) with an intramural (75% vs. 23%, p = 0.01) and septal (63% vs. 13%, p = 0.009) pattern. In a model including LV–EF (OR 0.8, 95% CI 0.7–1.0, p = NS) and LGE presence (OR 14.8, 95% CI 1.4–159.0, p = 0.026), only LGE was independently associated with the occurrence of Afib/Afl episodes. Conclusion: Myocardial abnormalities depicted by non-ischemic LGE-CMR were the only independent predictor for the occurrence of Afib/Afl on ECG monitoring, previously shown to predict adverse cardiac events in MD1. [ABSTRACT FROM AUTHOR]

Our current understanding of molecular mechanisms of cardiomyopathies has been elucidated from genetic animal models. Induced pluripotent stem cells (iPSCs) can provide a platform to improve our understanding of familial cardiomyopathies diseases. iPSCs are a type of pluripotent stem cell that can be generated directly from adult cells. Identification of mutations in patients with inherited cardiomyopathies has revealed substantial molecular complexity. In spite of the complexity, the advances of iPSC-based technology may improve our understanding of familial cardiomyopathies.

Cardiac fibrosis is a common phenomenon in different types of heart diseases, such as ischemic heart disease, inherited cardiomyopathy mutations, diabetes, and ageing and is associated with morbidity and mortality. Increased accumulation of extracellular matrix (ECM) that impacts cardiac function, is the underlying cause of fibrotic heart disease. There are four different types of cardiac fibrosis, including, reactive interstitial fibrosis, replacement fibrosis, infiltrative interstitial fibrosis and endomyocardial fibrosis. They are involved in the activation and transformation of cardiac fibroblasts to myofibroblasts, which participate in ECM production and fibrotic process and several inflammatory pathways. Besides the ECM proteins, myofibroblasts also express smooth muscle α-actin, SM22 and caldesmon and other markers related to fibrotic process. Most commonly employed techniques to assess myocardial fibrosis include stress echocardiography, cardiac magnetic resonance imaging and positron emission tomography. Because of the involvement of renin-angiotensin-II-aldosterone system, transforming growth factor-ß signaling and activin-linked kinase 5 in the mechanisms of cardiac fibrosis, these pathways and the involved proteins are useful as therapeutic targets. However, because of the importance of these pathways in many other physiological functions, their therapeutic targeting needs to be approached with caution. [ABSTRACT FROM AUTHOR]

Purpose of Review: Recently, the discovery of strategies to reprogram somatic cells into induced pluripotent stem (iPS) cells has led to a major paradigm change in developmental and stem cell biology. The application of iPS cells and their cardiac progeny has opened novel directions to study cardiomyopathies at a cellular and molecular level. This review discusses approaches currently undertaken to unravel known inherited cardiomyopathies in a dish. Recent Findings: With improved efficiency for mutation correction by genome editing, human iPS cells have now provided a platform to untangle the biology of cardiomyopathies. Multiple studies have derived pluripotent stem cells lines from patients with genetic heart diseases. The generation of cardiomyocytes from these cells lines has, for the first time, enable the study of cardiomyopathies using cardiomyocytes harboring patient-specific mutations and their corrected isogenic counterpart. The molecular analyses, functional assays, and drug tests of these lines have led to new molecular insights in the early pathophysiology of left ventricular non-compaction cardiomyopathy (LVNC), hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and others. Summary: The advent of iPS cells offers an exceptional opportunity for creating disease-specific cellular models to investigate their underlying mechanisms and to optimize future therapy through drug and toxicity screening. Thus far, the iPS cell model has improved our understanding of the genetic and molecular pathophysiology of patients with various genetic cardiomyopathies. It is hoped that the new discoveries arising from using these novel platforms for cardiomyopathy research will lead to new diagnostic and therapeutic approaches to prevent and treat these diseases. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate a cardiac MRI feature tracking (FT)-derived parameter that combines right ventricular (RV) longitudinal and radial motions in detecting arrhythmogenic right ventricular cardiomyopathy (ARVC)., Materials and Methods: Patients with ARVC ( n = 47; median age, 46 [IQR, 30-52] years; 31 men) were compared with controls ( n = 39; median age, 46 [IQR, 33-53] years; 23 men) and separated into two groups based on fulfillment of major structural 2020 International criteria. Cine data from 1.5-T cardiac MRI examinations were analyzed using FT, resulting in conventional strain parameters and a novel composite index named the longitudinal-to-radial strain loop (LRSL). Receiver operating characteristic (ROC) analysis was used to assess diagnostic performance of RV parameters., Results: Volumetric parameters differed significantly between patients in the major structural criteria group and controls but not between patients in the no major structural criteria group and controls. Patients in the major structural criteria group had significantly lower magnitudes of all FT parameters than controls, including RV basal longitudinal strain, radial motion fraction, circumferential strain, and LRSL (-15.6% ± 6.4 vs -26.7% ± 13.9; -9.6% ± 4.89 vs -13.8% ± 4.7; -6.9% ± 4.6 vs -10.1% ± 3.8; and 217.0 ± 128.9 versus 618.6 ± 356.3, respectively). Only LRSL differed between patients in the no major structural criteria group and controls (359.5 ± 195.8 vs 618.6 ± 356.3; P < .0001). Parameters with the highest area under the ROC curve values for discriminating patients in the no major structural criteria group from controls were LRSL, RV ejection fraction, and RV basal longitudinal strain (0.75, 0.70, and 0.61, respectively)., Conclusion: A new parameter combining RV longitudinal and radial motions showed good diagnostic performance in ARVC, even in patients without major structural abnormalities. Keywords: Arrhythmogenic Right Ventricular Dysplasia, Strain, Wall Motion Abnormalities, Right Ventricle, MRI, Inherited Cardiomyopathy Supplemental material is available for this article. © RSNA, 2023., Competing Interests: Disclosures of conflicts of interest: M.L. No relevant relationships. J.L. No relevant relationships. K.B.V. No relevant relationships. M.G. No relevant relationships. A. Giron No relevant relationships. A. Gallo Payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Sanofi, Amgen, Novartis, MSD, and Viatris; support for meeting attendance or travel from Amryt; participation on a Data Safety Monitoring Board or advisory board from Ultragenyx. P.C. No relevant relationships. E.G. No relevant relationships. A.R. Stock or stock options in Imageens. N.K. No relevant relationships., (© 2023 by the Radiological Society of North America, Inc.)

Familial cardiomyopathy is a precursor of heart failure and sudden cardiac death. Over the past several decades, researchers have discovered numerous gene mutations primarily in sarcomeric and cytoskeletal proteins causing two different disease phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathies. However, molecular mechanisms linking genotype to phenotype remain unclear. Here, we employ a systems approach by integrating experimental findings from preclinical studies (e.g., murine data) into a cohesive signaling network to scrutinize genotype to phenotype mechanisms. We developed an HCM/DCM signaling network model utilizing a logic-based differential equations approach and evaluated model performance in predicting experimental data from four contexts (HCM, DCM, pressure overload, and volume overload). The model has an overall prediction accuracy of 83.8%, with higher accuracy in the HCM context (90%) than DCM (75%). Global sensitivity analysis identifies key signaling reactions, with calcium-mediated myofilament force development and calcium-calmodulin kinase signaling ranking the highest. A structural revision analysis indicates potential missing interactions that primarily control calcium regulatory proteins, increasing model prediction accuracy. Combination pharmacotherapy analysis suggests that downregulation of signaling components such as calcium, titin and its associated proteins, growth factor receptors, ERK1/2, and PI3K-AKT could inhibit myocyte growth in HCM. In experiments with patient-specific iPSC-derived cardiomyocytes (MLP-W4R;MYH7-R723C iPSC-CMs), combined inhibition of ERK1/2 and PI3K-AKT rescued the HCM phenotype, as predicted by the model. In DCM, PI3K-AKT-NFAT downregulation combined with upregulation of Ras/ERK1/2 or titin or Gq protein could ameliorate cardiomyocyte morphology. The model results suggest that HCM mutations that increase active force through elevated calcium sensitivity could increase ERK activity and decrease eccentricity through parallel growth factors, Gq-mediated, and titin pathways. Moreover, the model simulated the influence of existing medications on cardiac growth in HCM and DCM contexts. This HCM/DCM signaling model demonstrates utility in investigating genotype to phenotype mechanisms in familial cardiomyopathy., Competing Interests: Declaration of Competing Interest A.D.M. and J.H.O. are co-founders of and have equity interests in Insilicomed Inc. and serve as scientific advisors. A.D.M is also a co-founder of and scientific advisor to Vektor Medical, Inc. Some of their research grants have been identified for conflict of interest management based on the overall scope of the project and its potential benefit to these companies. These authors are required to disclose this relationship in publications acknowledging the grant support; however, the research subject and findings reported in this study did not involve the companies in any way and had no relationship with the business activities or scientific interests of either company. The terms of this arrangement have been reviewed and approved by the University of California San Diego in accordance with its conflict of interest policies., (Copyright © 2022 Elsevier Ltd. All rights reserved.)