Search

Background: Mutation of MMACHC gene causes cobalamin C disease (cblC), an inherited metabolic disorder, which presents as combined methylmalonic aciduria (MMA-uria) and hyperhomocysteinaemia in clinical. Renal complications may also be present in patients with this inborn deficiency. The most common histological change is thrombotic microangiopathy (TMA). However, to our acknowledge, renal tubular injury in the late-onset presentation of cblC is rarely been reported. This study provides a detailed description of the characteristics of kidney disease in cblC deficiency, aiming to improve the early recognition of this treatable disease for clinical nephrologists. Case presentation: Here we described three teenage patients who presented with hematuria, proteinuria, and hypertension in clinical presentation. They were diagnosed with renal involvement due to cblC deficiency after laboratory tests revealing elevated serum and urine homocysteine, renal biopsy showing TMA and tubular injury, along with genetic testing showing heterogeneous compound mutations in MMACHC. Hydroxocobalamin, betaine, and L-carnitine were administered to these patients. All of them got improved, with decreased homocysteine, controlled blood pressure, and kidney outcomes recovered. Conclusions: The clinical diagnosis of cblC disease associated with kidney injury should be considered in patients with unclear TMA accompanied by a high concentration of serum homocysteine, even in teenagers or adults. Early diagnosis and timely intervention are vital to improving the prognosis of cobalamin C disease. Clinical Trial Number: Not applicable. [ABSTRACT FROM AUTHOR]

Amino acid (AA)-related inherited metabolic disorders (IMDs) and urea cycle disorders (UCDs) require strict dietary management including foods low in protein such as fruits, vegetables and starchy roots. Despite this recommendation, there are limited data on the AA content of many of these foods. The aim of this study is to describe an analysis of the protein and AA content of a range of fruits, vegetables and starchy roots, specifically focusing on amino acids (AAs) relevant to AA-related IMDs such as phenylalanine (Phe), methionine (Met), leucine (Leu), lysine (Lys) and tyrosine (Tyr). AA analysis was performed using high-performance liquid chromatography (HPLC) on 165 food samples. Protein analysis was also carried out using the Dumas method. Foods were classified as either 'Fruits', 'Dried fruits', 'Cruciferous vegetables', 'Legumes', 'Other vegetables' or 'Starchy roots'. 'Dried fruits' and 'Legumes' had the highest median values of protein, while 'Fruits' and 'Cruciferous vegetables' contained the lowest median results. 'Legumes' contained the highest and 'Fruits' had the lowest median values for all five AAs. Variations were seen in AA content for individual foods. The results presented in this study provide useful data on the protein and AA content of fruits, vegetables and starchy roots which can be used in clinical practice. This further expansion of the current literature will help to improve diet quality and metabolic control among individuals with AA-related IMDs and UCDs. [ABSTRACT FROM AUTHOR]

Background: Homocystinuria (HCU) is a rare metabolic disease that affects many organs, including the eyes. Aims: to assess visual functions, ocular characteristics, visual quality of life and time from the onset of ocular manifestations to HCU-diagnosis in patients with HCU. Material and methods: Eighteen patients underwent ophthalmological examinations and visual quality of life questionnaires. Results: Best corrected decimal visual acuity was median 1.0 (range amaurosis - 1.3) right eye and 1.0 (range amaurosis -1.3) left eye. Five patients presented with severe myopia as first HCU manifestation, duration to HCU diagnosis was mean 13.6 years (range 2-25). Two patients had suffered ectopia lentis as first HCU manifestation, HCU diagnosis was established mean 8.0 years (range 7-9) later. One patient had suffered both from thrombosis and ectopia lentis prior to diagnosis. Another four patients suffered thromboembolic events before diagnosis. Median VFQ-25 composite score was 93 (68-98). Conclusions: The prevalence of myopia, ectopia lentis and monocular blindness was high in HCU-patients, which was reflected in their visual quality of life. Diagnosis was often delayed after the first ocular manifestation, increasing the risk of other severe non-ocular complications. [ABSTRACT FROM AUTHOR]

Abstract Background Mutation of MMACHC gene causes cobalamin C disease (cblC), an inherited metabolic disorder, which presents as combined methylmalonic aciduria (MMA-uria) and hyperhomocysteinaemia in clinical. Renal complications may also be present in patients with this inborn deficiency. The most common histological change is thrombotic microangiopathy (TMA). However, to our acknowledge, renal tubular injury in the late-onset presentation of cblC is rarely been reported. This study provides a detailed description of the characteristics of kidney disease in cblC deficiency, aiming to improve the early recognition of this treatable disease for clinical nephrologists. Case presentation Here we described three teenage patients who presented with hematuria, proteinuria, and hypertension in clinical presentation. They were diagnosed with renal involvement due to cblC deficiency after laboratory tests revealing elevated serum and urine homocysteine, renal biopsy showing TMA and tubular injury, along with genetic testing showing heterogeneous compound mutations in MMACHC. Hydroxocobalamin, betaine, and L-carnitine were administered to these patients. All of them got improved, with decreased homocysteine, controlled blood pressure, and kidney outcomes recovered. Conclusions The clinical diagnosis of cblC disease associated with kidney injury should be considered in patients with unclear TMA accompanied by a high concentration of serum homocysteine, even in teenagers or adults. Early diagnosis and timely intervention are vital to improving the prognosis of cobalamin C disease. Clinical Trial Number Not applicable.

Cystathionine beta‐synthase‐deficient homocystinuria (HCU) is a life‐threatening disorder of sulfur metabolism. HCU can be treated by using betaine to lower tissue and plasma levels of homocysteine (Hcy). Here, we show that mice with severely elevated Hcy and potentially deficient in the folate species tetrahydrofolate (THF) exhibit a very limited response to betaine indicating that THF plays a critical role in treatment efficacy. Analysis of a mouse model of HCU revealed a 10‐fold increase in hepatic levels of 5‐methyl ‐THF and a 30‐fold accumulation of formiminoglutamic acid, consistent with a paucity of THF. Neither of these metabolite accumulations were reversed or ameliorated by betaine treatment. Hepatic expression of the THF‐generating enzyme dihydrofolate reductase (DHFR) was significantly repressed in HCU mice and expression was not increased by betaine treatment but appears to be sensitive to cellular redox status. Expression of the DHFR reaction partner thymidylate synthase was also repressed and metabolomic analysis detected widespread alteration of hepatic histidine and glutamine metabolism. Many individuals with HCU exhibit endothelial dysfunction. DHFR plays a key role in nitric oxide (NO) generation due to its role in regenerating oxidized tetrahydrobiopterin, and we observed a significant decrease in plasma NOx (NO2 + NO3) levels in HCU mice. Additional impairment of NO generation may also come from the HCU‐mediated induction of the 20‐hydroxyeicosatetraenoic acid generating cytochrome CYP4A. Collectively, our data shows that HCU induces dysfunctional one‐carbon metabolism with the potential to both impair betaine treatment and contribute to multiple aspects of pathogenesis in this disease. [ABSTRACT FROM AUTHOR]

Objectives: To study the clinical and molecular spectrum of Methylmalonic acidemia (MMA). Methods: In this retrospective study, the records of 30 MMA patients were evaluated for their phenotype, biochemical abnormalities, genotype, and outcomes. Results: Thirty patients with MMA (age range 0-21 y) from 27 unrelated families were enrolled. Family history and consanguinity were noted in 10/27 (37%) and 11/27 (41%) families respectively. Acute metabolic decompensation was more common (57%) than chronic presentation. Biochemical work-up was suggestive of isolated MMA (n = 18) and MMA with homocystinuria (n = 9) respectively. Molecular testing in 24 families showed 21 pathogenic or likely pathogenic variants with MMA cblC as the commonest molecular subtype (n = 8). B12 responsiveness, an important determinant of long-term outcome, was observed in eight patients [MMAA (n = 3) and MMACHC (n = 5)]. Mortality was 30% (n = 9/30) with a high proportion of early-onset severe disease and fatal outcome in isolated MMA mut0 (4/4) and MMA cblB (3/3), as compared to MMA cblA (1/5) and MMA cblC (1/10). Conclusions: This study cohort had MMA cblC subtype as the most common type of MMA followed by the MMA mutase defect. Outcomes in MMA are influenced by the type of molecular defect, age, and severity of presentation. Early detection and management is likely to result in better outcomes. [ABSTRACT FROM AUTHOR]

Classical homocystinuria is an inborn amino acid metabolism disorder resulting from mutations in the Cystathionine-β-Synthase (CBS) gene. These mutations lead to elevated homocysteine and methionine levels and reduced cysteine levels in the blood. Typically, diagnosis occurs after patients display symptoms, and various lab methods confirm it. DNA sequencing is the best option for early detection of genetic variants in asymptomatic suspected individuals. Unfortunately, its high cost can hinder its use, especially in low-income countries like Pakistan. Aim of this study was to devise a robust low-cost diagnostic/screening assay based on Tetra-ARMS-PCR for five prevalent genetic variants found in Pakistani classical homocystinuria patients. In the current study, T-ARMS-PCR assays were developed for five mutations (c.975G > C, c.770C > T, c.752T > C, c.1039 + 1G > T, c.451 + 1GG > TA), which were characterized previously in classical homocystinuria patients. These low-cost T-ARMS-PCR assays were then used to screen the affected individuals and their family members to identify their genotypes for pathogenic variations in the asymptomatic patients and carriers in their respective families. The outcomes were entirely consistent with those obtained from Sanger DNA sequencing, confirming the sensitivity, specificity, and reliability of the T-ARMS-PCR assay for detecting CBS mutations. T-ARMS-PCR has wide applications for low-income countries for the screening and early diagnosis of asymptomatic patients and carriers in the homocystinuria affected families as well as other inherited diseases. [ABSTRACT FROM AUTHOR]

Background: Cystathione beta-synthase (CBS) T236N is a novel mutation associated with pyridoxine non-responsiveness, which presents a significant difficulty in the medical treatment of homocystinuria. Reported severe phenotypes in homocystinuria patients highlight the urgent requirement to comprehend the molecular mechanisms underlying mutation pathogenicity for the advancement of the disease. Methodology: In this study, we used a multidisciplinary approach to investigate the molecular properties of bacterially expressed and purified recombinant CBST236N protein, which we directly compared to those of the wild-type (CBSWT) protein. Results: Our data revealed a profound impact of the p.T236N mutation on CBS enzymatic activity, with a dramatic reduction of ~96% compared to the CBSWT protein. Circular dichroism (CD) experiments indicated that the p.T236N mutation did not significantly alter the secondary structure of the protein. However, CD spectra unveiled distinct differences in the thermal stability of CBSWT and CBST236N mutant protein species. In addition, chemical denaturation experiments further highlighted that the CBSWT protein exhibited greater thermodynamic stability than the CBST236N mutant, suggesting a destabilizing effect of this mutation. Conclusions: Our findings provide an explanation of the pathogenicity of the p.T236N mutation, shedding light on its role in severe homocystinuria phenotypes. This study contributes to a deeper understanding of CBS deficiency and may improve the development of targeted therapeutic strategies for affected individuals. [ABSTRACT FROM AUTHOR]

Homocystinuria (HCU) due to cystathionine beta-synthase (CBS) deficiency is characterized by elevated plasma and tissue homocysteine levels. There is no cure, but HCU is typically managed by methionine/protein restriction and vitamin B6 supplementation. Enzyme replacement therapy (ERT) based on human CBS has been developed and has shown significant efficacy correcting HCU phenotype in several mouse models by bringing plasma total homocysteine below the clinically relevant 100 μM threshold. As the reactive nature of homocysteine promotes disulfide formation and protein binding, and ERT is unable to normalize plasma total homocysteine levels, the mechanism of action of ERT in HCU remains to be further characterized. Here we showed that only a reduced homocysteine serves as a substrate for CBS and its availability restricts the homocysteine-degrading capacity of CBS. We also demonstrated that cells export homocysteine in its reduced form, which is efficiently metabolized by CBS in the culture medium. Availability of serine, a CBS co-substrate, was not a limiting factor in our cell-based model. Biological reductants, such as N-acetylcysteine, MESNA or cysteamine, increased the availability of the reduced homocysteine and thus promoted its subsequent CBS-based elimination. In a transgenic I278T mouse model of HCU, administration of biological reductants significantly increased the proportion of protein-unbound homocysteine in plasma, which improved the efficacy of the co-administered CBS-based ERT, as evidenced by significantly lower plasma total homocysteine levels. These results clarify the mechanism of action of CBS-based ERT and unveil novel pharmacological approaches to further increase its efficacy.

Background: Based on research, c.609G>A (p.W203X) is a universal mutation site for MMACHC in methylmalonic acidemia (MMA) combined with homocystinuria, cblC type (cblC disease), and c.467G>A (p.G156D) mutation in families with such disease have not yet been reported. To conduct clinical and molecular genetic analysis of a family with cblC disease. Methods: This work followed the Declaration of Helsinki. All testing methods were performed under the informed consent of our children patients' parents. A second-generation cblC family with 5 members, was selected as the research subject, including sick siblings and parents and an older sister with normal phenotype, given newborn screening for acylcarnitine spectrum via liquid chromatography tandem mass spectrometry (LC-MS/MS), and diagnosed through combining urine organic acid with homocysteine detection via gas chromatography-mass spectrometry (GC-MS) with second-generation gene sequencing technology. The peripheral blood of five family members was collected for genomic DNA extraction, and the changes were screened in disease-related MMACHC sequence via PCR and direct DNA sequencing. Results: The family conformed to the autosomal recessive inheritance, the proband and younger sister were cblC patients, diagnosed in February and at 22d given relevant treatment. The proband died, whereas the younger sister received follow-up treatment. Their parents and sister had normal phenotype. In 2 cases, there was compound heterozygous mutation in MMACHC called c.609G>A (p.W203X) nonsense mutation and c.467G>A (p.G156D) missense mutation in exon 4, while the father with normal phenotype had heterozygous mutation c.609G>A in exon 4 coding area. In its protein, the 203rd amino acid changed from tryptophan to a stop codon (p.W203 x). The normal mother and sister had a heterozygous mutation c.467G>A in exon 4 coding area. In its protein, the 156th amino acid changed from glycine to aspartic acid (p.G156D). Conclusions: The cblC family results from c.609G>A (p.W203X) and c.467G>A (p.G156D) compound heterozygous mutations in MMACHC, which has a pathogenic impact. [ABSTRACT FROM AUTHOR]

Background: Cystathionine β-synthase (CBS)-deficient homocystinuria (HCU) is an inherited disorder of sulfur amino acid metabolism with varying severity and organ complications, and a limited knowledge about underlying pathophysiological processes. Here we aimed at getting an in-depth insight into disease mechanisms using a transgenic mouse model of HCU (I278T). Methods: We assessed metabolic, proteomic and sphingolipidomic changes, and mitochondrial function in tissues and body fluids of I278T mice and WT controls. Furthermore, we evaluated the efficacy of methionine-restricted diet (MRD) in I278T mice. Results: In WT mice, we observed a distinct tissue/body fluid compartmentalization of metabolites with up to six-orders of magnitude differences in concentrations among various organs. The I278T mice exhibited the anticipated metabolic imbalance with signs of an increased production of hydrogen sulfide and disturbed persulfidation of free aminothiols. HCU resulted in a significant dysregulation of liver proteome affecting biological oxidations, conjugation of compounds, and metabolism of amino acids, vitamins, cofactors and lipids. Liver sphingolipidomics indicated upregulation of the pro-proliferative sphingosine-1-phosphate signaling pathway. Liver mitochondrial function of HCU mice did not seem to be impaired compared to controls. MRD in I278T mice improved metabolic balance in all tissues and substantially reduced dysregulation of liver proteome. Conclusion: The study highlights distinct tissue compartmentalization of sulfur-related metabolites in normal mice, extensive metabolome, proteome and sphingolipidome disruptions in I278T mice, and the efficacy of MRD to alleviate some of the HCU-related biochemical abnormalities.

Purpose: To report the application of a refined total capsular bag suspension technique for lens subluxation from Cystathionine beta-synthase (CBS) deficiency. Observations: A 15-year-old CBS deficiency male patient with a history of intracranial venous thrombosis presented to our clinic due to bilateral vision loss. The patient was treated with lens aspiration, intraocular lens (IOL) implantation, and total capsular bag suspension in both eyes respectively. During the six months postoperative follow-up, the patient exhibited improved visual acuity and minor refractive error. Conclusions and importance: The refined total capsular bag suspension technique is recommended for CBS deficiency patients with lens subluxation as a safe and effective surgical approach.

Amino acid (AA)-related inherited metabolic disorders (IMDs) and urea cycle disorders (UCDs) require strict dietary management including foods low in protein such as fruits, vegetables and starchy roots. Despite this recommendation, there are limited data on the AA content of many of these foods. The aim of this study is to describe an analysis of the protein and AA content of a range of fruits, vegetables and starchy roots, specifically focusing on amino acids (AAs) relevant to AA-related IMDs such as phenylalanine (Phe), methionine (Met), leucine (Leu), lysine (Lys) and tyrosine (Tyr). AA analysis was performed using high-performance liquid chromatography (HPLC) on 165 food samples. Protein analysis was also carried out using the Dumas method. Foods were classified as either ‘Fruits’, ‘Dried fruits’, ‘Cruciferous vegetables’, ‘Legumes’, ‘Other vegetables’ or ‘Starchy roots’. ‘Dried fruits’ and ‘Legumes’ had the highest median values of protein, while ‘Fruits’ and ‘Cruciferous vegetables’ contained the lowest median results. ‘Legumes’ contained the highest and ‘Fruits’ had the lowest median values for all five AAs. Variations were seen in AA content for individual foods. The results presented in this study provide useful data on the protein and AA content of fruits, vegetables and starchy roots which can be used in clinical practice. This further expansion of the current literature will help to improve diet quality and metabolic control among individuals with AA-related IMDs and UCDs.

Hyperhomocysteinemia (HHcy) is recognized as an independent risk factor for various significant medical conditions, yet controversy persists around its assessment and management. The diagnosis of disorders afffecting homocysteine (Hcy) metabolism faces delays due to insufficient awareness of its clinical presentation and unique biochemical characteristics. In cases of arterial or venous thrombotic vascular events, particularly with other comorbidities, it is crucial to consider moderate to severe HHcy. A nutritional approach to HHcy management involves implementing dietary strategies and targeted supplementation, emphasizing key nutrients like vitamin B6, B12, and folate that are crucial for Hcy conversion. Adequate intake of these vitamins, along with betaine supplementation, supports Hcy remethylation. Lifestyle modifications, such as smoking cessation and regular physical activity, complement the nutritional approach to enhance Hcy metabolism. For individuals with HHcy, maintaining a plasma Hcy concentration below 50 μmol/L consistently is vital to lowering the risk of vascular events. Collaboration with healthcare professionals and dietitians is essential for developing personalized dietary plans addressing the specific needs and underlying health conditions. This integrated approach aims to optimize metabolic processes and reduce the associated health risks. [ABSTRACT FROM AUTHOR]

Copyright of Revista Mexicana de Endocrinología, Metabolismo y Nutrición is the property of Publicidad Permanyer SLU and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Homocystinuria (HCU), an inherited metabolic disorder caused by lack of cystathionine beta-synthase (CBS) activity, is chiefly caused by misfolding of single amino acid residue missense pathogenic variants. Previous studies showed that chemical, pharmacological chaperones or proteasome inhibitors could rescue function of multiple pathogenic CBS variants; however, the underlying mechanisms remain poorly understood. Using Chinese hamster DON fibroblasts devoid of CBS and stably overexpressing human WT or mutant CBS, we showed that expression of pathogenic CBS variant mostly dysregulates gene expression of small heat shock proteins HSPB3 and HSPB8 and members of HSP40 family. Endoplasmic reticulum stress sensor BiP was found upregulated with CBS I278T variant associated with proteasomes suggesting proteotoxic stress and degradation of misfolded CBS. Co-expression of the main effector HSP70 or master regulator HSF1 rescued steadystate levels of CBS I278T and R125Q variants with partial functional rescue of the latter. Pharmacological proteostasis modulators partially rescued expression and activity of CBS R125Q likely due to reduced proteotoxic stress as indicated by decreased BiP levels and promotion of refolding as indicated by induction of HSP70. In conclusion, targeted manipulation of cellular proteostasis may represent a viable therapeutic approach for the permissive pathogenic CBS variants causing HCU. [ABSTRACT FROM AUTHOR]

A novel, rapid, selective, ultrasensitive, and ultra-reproducible spectrofluorometric nanoassay was designed for the L-methionine quantification. A carbon dot with a %QY as high as 95% was prepared using a solvent-free ultrafast method and used as the label-free nanoprobe. The nanoprobe was characterized for size, morphology, elemental composition, optical properties, and quantum efficiency. Afterward, the nanoprobe was utilized for quantification of L-methionine in biological samples, revealing an ultra-wide linear range of 0.0–140.0 nm with a LOD as low as 0.65 nM. Besides, the developed method showed ultra-reproducibility with an inter-week assay, of RSD = 2.7% and high repeatability with a RSD as low as 1.0%. The mechanistic studies proved the simultaneous formation of two complexes between CDs and L-methionine, resulting in high sensitivity, selectivity, and stability of the sensor. Moreover, a binding constant as high as 1.4 × 10+6 M−1, number of binding sites of 1.5, and a ∆G of − 35.1 was obtained for interaction between CDs and L-methionine. Finally, the developed method was utilized for analysis of the methionine content of human serum samples for both healthy and patients with homocystinuria for proving its possible application in homocystinuria diagnosis, showing highly accurate and reproducible results. Consequently, the proposed nanoassay can be applied for clinical practical applications toward homocystinuria diagnosis. [ABSTRACT FROM AUTHOR]

Cobalamin C disease is the most common complementation class of cobalamin disorders. Here, we present a case of a 14-yr-old male with early-onset cblC disease and autism spectrum disorder (ASD) admitted to our inpatient medical service for behavioral decompensation. We use this case to highlight key aspects of the neurodevelopmental and neuropsychiatric disorders associated with cblC disease. By incorporating a comprehensive review of existing literature, we highlight salient domains of psychological impairment in cblC disease, discuss the full range of neuropsychiatric presentations, and review clinical management implications unique to cblC disease.

Human milk (HM) offers important nutritional benefits. However, except for phenylketonuria (PKU), there are little data on optimal levels of consumption of HM and a special formula free of disease-related amino acids (SF-AA) in infants with inborn errors of metabolism of amino acids and proteins (IEM-AA-P). We designed a spreadsheet to calculate the amounts of SF-AA and HM required to cover amino acid, protein, and energy needs in patients with the nine main IEM-AA-P in infants aged under 6 months. Upon entering the infant's weight and the essential amino acid or intact protein requirements for the specific IEM, the spreadsheet calculates the corresponding required volume of HM based on the amino acid concentration in HM. Next, the theoretical daily fluid intake (typical range, 120–200 mL/kg/day) is entered, and the estimated daily fluid intake is calculated. The required daily volume of SF-AA is calculated as the difference between the total fluid intake value and the calculated volume of HM. The spreadsheet allows for the introduction of a range of requirements based on the patient's metabolic status, and includes the option to calculate the required volume of expressed HM, which may be necessary in certain conditions such as MMA/PA and UCD. In cases in which breastfeeding on demand is feasible, the spreadsheet determines the daily amount of SF-AA divided over 6–8 feeds, assuming that SF-AA is administered first, followed by HM as needed. Intake data calculated by the spreadsheet should be evaluated in conjunction with data from clinical and nutritional analyses, which provide a comprehensive understanding of the patient's nutritional status and help guide individualized dietary management for the specific IEM. [ABSTRACT FROM AUTHOR]

Homocystinuria is a rare genetic disease with autosomal recessive pattern. It is reported to be highest in Arabian descend and could cause thrombosis, but mainly peripherally. Cardiac amorphous tumor has been recognized in the past 20 years and it is also a very rare cause primary benign tumor of the heart. Most of the cases reported to be associated with end-stage renal disease. Homocystinuria associated with Cardiac Amorphous tumor is extremely rare. Up to our knowledge, there has been only one other case has been reported. Our patient is a 14-year-old female known case of homocystinuria presented with dyspnea and leg edema. On workup was found to have a mass in the right atrium extending to superior vena cava and inferior cava. Surgery undertaken on cardiopulmonary bypass partial resection of the mass was done and result came back as cardiac amorphous tumor. We assume the cause of this sinister complication of her primary illness is calcification of thrombus as stated in literature. And also recommend further studies regarding issue on hand.

BackgroundFor the majority of rare clinical missense variants, pathogenicity status cannot currently be classified. Classical homocystinuria, characterized by elevated homocysteine in plasma and urine, is caused by variants in the cystathionine beta-synthase (CBS) gene, most of which are rare. With early detection, existing therapies are highly effective.MethodsDamaging CBS variants can be detected based on their failure to restore growth in yeast cells lacking the yeast ortholog CYS4. This assay has only been applied reactively, after first observing a variant in patients. Using saturation codon-mutagenesis, en masse growth selection, and sequencing, we generated a comprehensive, proactive map of CBS missense variant function.ResultsOur CBS variant effect map far exceeds the performance of computational predictors of disease variants. Map scores correlated strongly with both disease severity (Spearman's ϱ = 0.9) and human clinical response to vitamin B6 (ϱ = 0.93).ConclusionsWe demonstrate that highly multiplexed cell-based assays can yield proactive maps of variant function and patient response to therapy, even for rare variants not previously seen in the clinic.

Background: Cystathione beta-synthase (CBS) T236N is a novel mutation associated with pyridoxine non-responsiveness, which presents a significant difficulty in the medical treatment of homocystinuria. Reported severe phenotypes in homocystinuria patients highlight the urgent requirement to comprehend the molecular mechanisms underlying mutation pathogenicity for the advancement of the disease. Methodology: In this study, we used a multidisciplinary approach to investigate the molecular properties of bacterially expressed and purified recombinant CBST236N protein, which we directly compared to those of the wild-type (CBSWT) protein. Results: Our data revealed a profound impact of the p.T236N mutation on CBS enzymatic activity, with a dramatic reduction of ~96% compared to the CBSWT protein. Circular dichroism (CD) experiments indicated that the p.T236N mutation did not significantly alter the secondary structure of the protein. However, CD spectra unveiled distinct differences in the thermal stability of CBSWT and CBST236N mutant protein species. In addition, chemical denaturation experiments further highlighted that the CBSWT protein exhibited greater thermodynamic stability than the CBST236N mutant, suggesting a destabilizing effect of this mutation. Conclusions: Our findings provide an explanation of the pathogenicity of the p.T236N mutation, shedding light on its role in severe homocystinuria phenotypes. This study contributes to a deeper understanding of CBS deficiency and may improve the development of targeted therapeutic strategies for affected individuals.

Background: Cystathionine beta synthase deficiency (causing classical homocystinuria) has been associated with high-arched palates and crowded teeth, but little has been said about other oral health complications. Other homocystinurias (e.g., the remethylation defects) also have had little reported in terms of oral health. Individuals with the homocystinurias have been described as having bone density issues which can correlate with oral health. Moreover, elevations in homocysteine have a theoretical impact on tooth health and the paucity of clinical reports of oral health issues in homocystinuria may be the consequence of lack of attention by the medical community. Significance: Oral health is essential to overall health. If inadequate attention is paid to the oral health complications which can be seen in homocystinurias, then appropriate referrals and attention in therapeutic guidelines will not reflect the importance of oral health. Specific aims/research question: What oral health complications are reported by individuals with homocystinurias? Do these differ according to diagnosis? Methods: Data were collected from patients with homocystinurias by a series of questionnaires using the RARE-X platform. All subjects were consented prior to the collection of their data. All research was performed in accordance with the Declaration of Helsinki. Demographic data were collected as the initial questionnaire and other data were collected via the oral health questionnaire. Analysis: Questionnaires were opened to the community in mid-2022 and collection of data for this study ended with data submitted up to November 2022. Descriptive statistics were done. Due to the small size of the cohort, additional statistical analyses were not attempted. Results: Patients with homocystinuria, not related to cystathionine beta synthase deficiency, are reporting some tooth structure differences. The cohort taken as a whole does not have increased risk for gingivitis, but there appears to be a risk for long-term gum disease possibly due to the rate of osteoporosis/osteopenia in this population. A large number of individuals have malalignment and malocclusion of the teeth. These data highlight oral health as an important component of care in individuals with the homocystinurias as is true of the general population at large.

The main treatment for pyridoxine-nonresponsive cystathionine-β-synthase deficiency is a strict diet. Most centers prescribe low-protein diets based on gram–protein exchanges, and all protein sources are weighed. The purpose of this study is to investigate the effects of a more liberal methionine (Met)-based diet with relaxed consumption of fruits and vegetables on metabolic outcomes and dietary adherence. Ten patients previously on a low-protein diet based on a gram–protein exchange list were enrolled. The natural protein exchange lists were switched to a "Met portion exchange list". Foods containing less than 0.005 g methionine per 100 g of the food were accepted as exchange-free foods. The switch to Met portioning had no adverse effects on the control of plasma homocysteine levels in terms of metabolic outcomes. It resulted in a significant reduction in patients' daily betaine dose. All patients preferred to continue with this modality. In conclusion, methionine-portion-based medical nutrition therapy with relaxed consumption of fruits and vegetables seems to be a good and safe option to achieve good metabolic outcomes and high treatment adherence. [ABSTRACT FROM AUTHOR]

Acute encephalopathy is a critical medical condition that typically affects previously healthy children and young adults and often results in death or severe neurological sequelae. Inherited metabolic diseases that can cause acute encephalopathy include urea cycle disorders, amino acid metabolism disorders, organic acid metabolism disorders, fatty acid metabolism disorders, mutations in the thiamine-transporter gene, and mitochondrial diseases. Although each inherited metabolic disease is rare, its overall incidence is reported as 1 in 800–2500 patients. This narrative review presents the common inherited metabolic diseases that cause acute encephalopathy. Since diagnosing inherited metabolic diseases requires specific testing, early metabolic/metanolic screening tests are required when an inherited metabolic disease is suspected. We also describe the symptoms and history associated with suspected inherited metabolic diseases, the various tests that should be conducted in case of suspicion, and treatment according to the disease group. Recent advancements made in the understanding of some of the inherited metabolic diseases that cause acute encephalopathy are also highlighted. Acute encephalopathy due to inherited metabolic diseases can have numerous different causes, and recognition of the possibility of an inherited metabolic disease as early as possible, obtaining appropriate specimens, and proceeding with testing and treatment in parallel are crucial in the management of these diseases. [ABSTRACT FROM AUTHOR]

Background: Classical homocystinuria (HCU) is an inborn defect of methionine metabolism caused by a deficiency of the enzyme cystathionine β-synthase (CBS). The main symptoms of classical homocystinuria are lens subluxation, bone lesions, vascular disease and developmental delay/intellectual disability. The treatment method for HCU is a methionine-poor diet supplemented with amino acid preparations. The aim of the study was to examine the relationship of dietary factors, metabolic compensation and selected skeletal parameters in patients with HCU. Methods: Bone mineral density measurements (DXA) were performed in pediatric patients with HCU, and blood levels of selected amino acids, minerals and vitamins, as well as dietary nutritional value, were analyzed. Results: A total of 11 patients with HCU whose median age was 9.3 years were enrolled in the study. The median DXA total body less head of HCU patients was −0.4 z-score, and the lumbar spine was −1.4 z-score. Despite supplementation, calcium intake was below the age norm. Average vitamin D3 intake was in line with recommendations, but 36% of patients had reduced blood levels. Bone mineral density depended on blood levels of 25-hydroxyvitamin D, homocysteine and methionine, as well as on BMI, age and intake of natural protein (R2 = 98.5%, p = 0.015; R2 = 86.7%, p = 0.0049) and protein from an amino acid preparation (r = 0.69, p = 0.026). Conclusion: The results of the study indicate the need for regular densitometry in patients with HCU and also the use of additional calcium and vitamin D3 supplementation. It is also necessary to perform a comprehensive analysis of the diet and metabolic controls. [ABSTRACT FROM AUTHOR]

CBS deficient individuals undergoing betaine supplementation without sufficient dietary methionine restriction can develop severe hypermethioninemia and brain edema. Brain edema has also been observed in individuals with severe hypermethioninemia without concomitant betaine supplementation. We systematically evaluated reports from 11 published and 4 unpublished patients with CBS deficiency and from additional four cases of encephalopathy in association with elevated methionine. We conclude that, while betaine supplementation does greatly exacerbate methionine accumulation, the primary agent causing brain edema is methionine rather than betaine. Clinical signs of increased intracranial pressure have not been seen in patients with plasma methionine levels below 559 μmol/L but occurred in one patient whose levels did not knowingly exceed 972 μmol/L at the time of manifestation. While levels below 500 μmol/L can be deemed safe it appears that brain edema can develop with plasma methionine levels close to 1000 μmol/L. Patients with CBS deficiency on betaine supplementation need to be regularly monitored for concordance with their dietary plan and for plasma methionine concentrations. Recurrent methionine levels above 500 μmol/L should alert clinicians to check for clinical signs and symptoms of brain edema and review dietary methionine intake. Levels approaching 1000 μmol/L do increase the risk of complications and levels exceeding 1000 μmol/L, despite best dietetic efforts, should be acutely addressed by reducing the prescribed betaine dose.

Abstract Background Homocystinuria due to methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare autosomal recessive disorder. The purpose of this study is to expand the mutation site of the MTHFR gene and provide genetic counseling for this family. Methods A couple came to our hospital for pre-pregnancy genetic counseling. We collected the family history and detailed clinical information, then performed whole-exome sequencing, and analyzed the pathogenicity of the candidate mutations. Results We found that the father of the proband had homocystinuria, the proband and his brother had low blood methionine levels at birth, and the brain MRI showed brain dysplasia. The third fetus was found to have a broadened triangle of the bilateral ventricle at 19 weeks of pregnancy. The compound heterozygous variants of c.602 A > C (p.His201Pro) and c.1316T > C (p.Leu439Pro) of the MTHFR gene in the first three fetuses were found by whole-exome sequencing. The heterozygous c.602 A > C variant of the MTHFR gene is a novel missense variant that has been submitted to the ClinVar with Variation ID 992,662. Conclusion In consideration of the clinical phenotype, family history, and result of genetic testing, we speculated that both patients may have homocystinuria due to MTHFR deficiency. Homocystinuria due to MTHFR deficiency caused by compound heterozygous mutations composed of the MTHFR gene in this family may be associated with cerebral atrophy and cerebral dysplasia. The novel compound heterozygous mutations broaden the mutation spectrum of the MTHFR gene and enhance the application of genetic counseling and carrier screening in rare diseases.

Abstract Background Homocystinuria is an inherited, inborn error of homocysteine metabolism, which leads to the abnormal accumulation of homocysteine and its metabolites in blood and urine, resulting in various complications. Variants in the cystathionine β-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR) genes interrupt the formation of the corresponding enzymes and prevent homocysteine from being metabolised; hence, the homocysteine levels in plasma increase than the optimum levels. Materials and methods In the current study, eight clinically confirmed children with homocystinuria were detected to study the chosen variants in the CBS gene (c.833 T>C and c.19del) and in the MTHFR gene (c.665 C>T, c.1286 A>C) using SNaPshot mini-sequencing and direct sequencing. Results After screening eight patients, none had the c.833T>C, but four patients were in the homozygous state for the c.19del variant in the CBS gene. Furthermore, seven were heterozygous for c.1286A>C, while one patient was heterozygous for c.665C>T in the MTHFR gene. Conclusion According to the results, c.19del is common in the studied cohort of Sri Lankan children, while c.833T>C is absent, whereas c.1286A>C was more frequent than c.665C>T. To our knowledge, the current study was the first report to discuss the genetic impact of homocystinuria in Sri Lanka; further comprehensive studies are necessary with a larger sample size to establish the association of these variants with the disease in Sri Lanka, which can be beneficial in enhanced patient care and for prospective studies.

Cystathionine beta‐synthase (CBS)‐deficient homocystinuria (HCU) is the most common inborn error of sulfur amino acid metabolism. The pyridoxine non‐responsive form of the disease manifests itself by massively increasing plasma and tissue concentrations of homocysteine, a toxic intermediate of methionine metabolism that is thought to be the major cause of clinical complications including skeletal deformities, connective tissue defects, thromboembolism and cognitive impairment. The current standard of care involves significant dietary interventions that, despite being effective, often adversely affect quality of life of HCU patients, leading to poor adherence to therapy and inadequate biochemical control with clinical complications. In recent years, the unmet need for better therapeutic options has resulted in development of novel enzyme and gene therapies and exploration of pharmacological approaches to rescue CBS folding defects caused by missense pathogenic mutations. Here, we review scientific evidence and current state of affairs in development of recent approaches to treat HCU. [ABSTRACT FROM AUTHOR]