Clinical and genetic analysis of methylmalonic aciduria in 60 patients from Southern China: a single center retrospective study.

BACKGROUND: Methylmalonic aciduria (MMA) is a group of rare genetic metabolic disorders resulting from defects in methylmalonyl coenzyme A mutase (MCM) or intracellular cobalamin (cbl) metabolism. MMA patients show diverse clinical and genetic features across different subtypes and populations. METHODS: We retrospectively recruited 60 MMA patients from a single center and diagnosed them based on their clinical manifestations and biochemical assays. We then performed genetic analysis to confirm the diagnosis and identify the causal variants. RESULTS: We confirmed the common clinical manifestations of MMA reported previously. We also described four rare MMA cases with unusual symptoms or genetic variants, such as pulmonary hypertension or limb weakness in late-onset patients. We identified 15 MMACHC and 26 MMUT variants in 57 patients, including 6 novel MMUT variants. Two patients had only one MMAA variant each, and one patient had mild MMA due to mitochondrial DNA depletion syndrome caused by a SUCLA2 variant. Among 12 critically ill patients, isolated MMA was associated with higher C3, blood ammonia, and acidosis, while combined MMA was linked to hydrocephalus on skull MRI. MMACHC c.658-660delAAG and MMUT c.1280G > A variants were correlated with more severe phenotypes. CONCLUSIONS: Our study demonstrates the clinical and genotypic heterogeneity of MMA patients and indicates that metabolic screening and genetic analysis are useful tools to identify rare cases.

Outcomes after newborn screening for propionic and methylmalonic acidemia and homocystinurias.

The current German newborn screening (NBS) panel includes 13 inherited metabolic diseases (IMDs). In addition, a NBS pilot study in Southwest Germany identifies individuals with propionic acidemia (PA), methylmalonic acidemia (MMA), combined and isolated remethylation disorders (e.g., cobalamin [cbl] C and methylenetetrahydrofolate reductase [MTHFR] deficiency), cystathionine ß-synthase (CBS) deficiency, and neonatal cbl deficiency through one multiple-tier algorithm. The long-term health benefits of screened individuals are evaluated in a multicenter observational study. Twenty seven screened individuals with IMDs (PA [N = 13], MMA [N = 6], cblC deficiency [N = 5], MTHFR deficiency [N = 2] and CBS deficiency [N = 1]), and 42 with neonatal cbl deficiency were followed for a median of 3.6 years. Seventeen screened IMD patients (63%) experienced at least one metabolic decompensation, 14 of them neonatally and six even before the NBS report (PA, cbl-nonresponsive MMA). Three PA patients died despite NBS and immediate treatment. Fifteen individuals (79%) with PA or MMA and all with cblC deficiency developed permanent, mostly neurological symptoms, while individuals with MTHFR, CBS, and neonatal cbl deficiency had a favorable clinical outcome. Utilizing a combined multiple-tier algorithm, we demonstrate that NBS and specialized metabolic care result in substantial benefits for individuals with MTHFR deficiency, CBS deficiency, neonatal cbl deficiency, and to some extent, cbl-responsive MMA and cblC deficiency. However, its advantage is less evident for individuals with PA and cbl-nonresponsive MMA. SYNOPSIS: Early detection through newborn screening and subsequent specialized metabolic care improve clinical outcomes and survival in individuals with MTHFR deficiency and cystathionine-ß-synthase deficiency, and to some extent in cobalamin-responsive methylmalonic acidemia (MMA) and cblC deficiency while the benefit for individuals with propionic acidemia and cobalamin-nonresponsive MMA is less evident due to the high (neonatal) decompensation rate, mortality, and long-term complications.

The MMACHC variant c.158T>C: Mild clinical and biochemical phenotypes and marked hydroxocobalamin response in cblC patients.

Mutations in MMACHC cause cobalamin C disease (cblC, OMIM 277400), the commonest inborn error of vitamin B12 metabolism. In cblC, deficient activation of cobalamin results in methylcobalamin and adenosylcobalamin deficiency, elevating methylmalonic acid (MMA) and total plasma homocysteine (tHcy). We retrospectively reviewed the medical files of seven cblC patients: three compound heterozygotes for the MMACHC (NM_015506.3) missense variant c.158T>C p.(Leu53Pro) in trans with the common pathogenic mutation c.271dupA (p.(Arg91Lysfs*14), "compounds"), and four c.271dupA homozygotes ("homozygotes"). Compounds receiving hydroxocobalamin intramuscular injection monotherapy had age-appropriate psychomotor performance and normal ophthalmological examinations. In contrast, c.271dupA homozygotes showed marked psychomotor retardation, retinopathy and feeding problems despite penta-therapy (hydroxocobalamin, betaine, folinic acid, l-carnitine and acetylsalicylic acid). Pretreatment levels of plasma and urine MMA and tHcy were higher in c.271dupA homozygotes than in compounds. Under treatment, levels of the compounds approached or entered the reference range but not those of c.271dupA homozygotes (tHcy: compounds 9.8-32.9 µM, homozygotes 41.6-106.8 (normal (N) < 14); plasma MMA: compounds 0.14-0.81 µM, homozygotes, 10.4-61 (N < 0.4); urine MMA: compounds 1.75-48 mmol/mol creatinine, homozygotes 143-493 (N < 10)). Patient skin fibroblasts all had low cobalamin uptake, but this was milder in compound cells. Also, the distribution pattern of cobalamin species was qualitatively different between cells from compounds and from homozygotes. Compared to the classic cblC phenotype presented by c.271dupA homozygous patients, c.[158T>C];[271dupA] compounds had mild clinical and biochemical phenotypes and responded strikingly to hydroxocobalamin monotherapy.

Methylmalonyl Coenzyme A (CoA) Epimerase Deficiency, an Ultra-Rare Cause of Isolated Methylmalonic Aciduria With Predominant Neurological Features.

Methylmalonyl coenzyme A (CoA) epimerase (MCE) converts D-methylmalonyl-CoA into L-methylmalonyl CoA in the final common degradation pathway of valine, isoleucine, methionine, threonine, odd-chain fatty acids, and cholesterol side chains. Methylmalonyl-CoA epimerase deficiency is an ultra-rare autosomal recessive disorder where methylmalonic acid, methylcitrate, 3-hydroxypropionate, and propionylcarnitine are accumulated. We describe two novel pediatric patients and review the previously reported cases of MCE deficiency. Including our two novel patients, at least 24 cases of MCE deficiency have been described, with a broad clinical spectrum ranging from asymptomatic to severely neurologically impaired patients. Our patients are siblings of Arabic origin who presented with metabolic decompensation with coma and epilepsy during infancy. Methylmalonic aciduria was disclosed, L-methylmalonyl-CoA mutase deficiency was assumed, and they were treated accordingly. When first seen in our country, aged 10 and four years, respectively, both presented severe intellectual disability and spasticity. The younger had an ataxic gait, and the older was wheelchair-ridden. The study of the MMUT, MMAA, MMAB, and MMADHC genes was normal. Subsequently, the pathogenic variant c.139C>T (p.Arg47*) in the MCEE gene was identified in homozygosity in both patients, leading to the diagnosis of MCE deficiency (Online Mendelian Inheritance in Man (OMIM®) 251120, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University, MD, USA). Most patients were homozygous for that variant (83% of the alleles). Correct diagnosis allowed treatment adequacy and genetic counseling. Methylmalonyl-CoA epimerase deficiency shares a similar biochemical profile with other rare genetic disorders. Patients present with overlapping clinical features with predominant neurological manifestations; genetic testing is indispensable for diagnosis. We found no association between genotype and biochemical and clinical phenotypes.

Combined Malonic and Methylmalonic Aciduria Diagnosed by Recurrent and Severe Infections Mimicking a Primary Immunodeficiency Disease: A Case Report.

Combined malonic and methylmalonic aciduria is a rare genetic disorder caused by ACSF3 biallelic variants that results in impaired protein and fat metabolism and the accumulation of malonic and methylmalonic acids. A 52-day-old infant with a fever and a history of possible meningitis during the neonatal period was hospitalized. Multiple lesions of necrotizing lymphadenitis with abscesses in the left inguinal area were treated by incision and drainage along with appropriate antibiotic therapy, which revealed a methicillin-resistant Staphylococcus aureus infection. At 6 months of age, the patient was admitted with anal abscesses. Due to the increased suspicion of primary immunodeficiency disease, genetic testing was conducted, which revealed ACSF3 biallelic variants inherited from both parents. Urine organic acid analysis revealed elevated levels of malonic and methylmalonic acids. At 29 months, the patient showed normal growth and development without any dietary modifications. He had occasional colds, but severe bacterial infections were absent. The prognosis suggests a benign disease course. Here, we present the first reported case of ACSF3 compound heterozygote variants in Korea.

Safety, efficacy, and timing of transplantation(s) in propionic and methylmalonic aciduria.

Propionic (PA) and methylmalonic aciduria (MMA) share many clinical similarities, which include the risk of acute metabolic encephalopathies, and some long-term complications, such as optic neuropathy, pancreatic involvement, developmental disability, and similar management approaches, but they also represent distinct clinical and biochemical entities. In the severe forms of PA and MMA, most long-term complications cannot be prevented with conventional clinical management. Organ transplantation represents a form of partial enzyme replacement to improve the long-term outlook for these disorders. There is evidence that early liver transplant in both disorders greatly improves metabolic stability and reduces the risk of long-term complications. For MMA, early liver transplant reduces methylmalonic acid levels which in turns reduces its effects on kidneys, and therefore slows progression of chronic kidney disease. However, established organ damage cannot be reversed. For patients with MMA who present with chronic kidney disease, consideration should be given for combined liver and kidney transplants. Transplantation in PA and MMA carries a high risk of complications and requires highly specialised pre-operative and peri-operative management. Involvement of a multidisciplinary team is essential and should include metabolic team, nephrologist, hepatologist, hepatobiliary and renal transplant surgeons, anaesthesiologists, cardiologists, intensive care team, dieticians and specialist nurses. These patients require life-long multidisciplinary follow-up. There is increasing evidence in the literature on excellent short to medium-term patient and allograft survival following transplantation when patients are managed by a multidisciplinary team in a specialist centre. Improved early diagnosis and reductions in transplant-related mortality and morbidity have allowed early transplantation to be used electively to further improve the outcome.

A regionally adapted HRM-based technique to screen MMACHC carriers for methylmalonic acidemia with homocystinuria in Shandong Province, China.

Methylmalonic acidemia with homocystinuria (MMA-cblC) is an autosomal recessive genetic disorder of organic acid metabolism. Shandong, a northern province of China, has a significantly high incidence of about 1/4,000, suggesting a high carrying rate among the local population. The current study established a PCR technique involving high-resolution melting (HRM) to screen for carriers based on hotspot mutation analysis to further develop a preventive strategy to reduce the local incidence of this rare disease. Whole-exome sequencing of 22 families with MMA-cblC and a comprehensive literature review were used to identify MMACHC hotspot mutations in Shandong Province. Subsequently, a PCR-HRM assay based on the selected mutations was established and optimized for large-scale hotspot mutation screening. The accuracy and efficiency of the screening technique was validated using samples from 69 individuals with MMA-cblC and 1,000 healthy volunteers. Six hotspot mutations in the MMACHC gene (c.609G>A, c.658_660delAAG, c.80A>G, c.217C>T, c.567dupT and c.482G>A), which account for 74% of the alleles associated with MMA-cblC, were used to establish a screening technique. The established PCR-HRM assay detected 88 MMACHC mutation alleles in a validation study with 100% accuracy. In the general population in Shandong, the carrying rate of 6 MMACHC hotspot mutations was 3.4%. In conclusion, the 6 hotspots identified cover the majority of the MMACHC mutation spectrum, and the Shandong population has a particularly high carrying rate of MMACHC mutations. The PCR-HRM assay is highly accurate, cost-effective, and easy to use, making it an ideal choice for mass carrier screening.

Neurologic outcome following liver transplantation for methylmalonic aciduria.

Liver and liver/kidney transplantation are increasingly used in methylmalonic aciduria, but little is known on their impact on CNS. The effect of transplantation on neurological outcome was prospectively assessed in six patients pre- and post-transplant by clinical evaluation and by measuring disease biomarkers in plasma and CSF, in combination with psychometric tests and brain MRI studies. Primary (methylmalonic- and methylcitric acid) and secondary biomarkers (glycine and glutamine) significantly improved in plasma, while they remained unchanged in CSF. Differently, biomarkers of mitochondrial dysfunction (lactate, alanine, and related ratios) significantly decreased in CSF. Neurocognitive evaluation documented significant higher post-transplant developmental/cognitive scores and maturation of executive functions corresponding to improvement of brain atrophy, cortical thickness, and white matter maturation indexes at MRI. Three patients presented post-transplantation reversible neurological events, which were differentiated, by means of biochemical and neuroradiological evaluations, into calcineurin inhibitor-induced neurotoxicity and metabolic stroke-like episode. Our study shows that transplantation has a beneficial impact on neurological outcome in methylmalonic aciduria. Early transplantation is recommended due to the high risk of long-term complications, high disease burden, and low quality of life.

How guideline development has informed clinical research for organic acidurias (et vice versa).

Organic acidurias, such as glutaric aciduria type 1 (GA1), methylmalonic (MMA), and propionic aciduria (PA) are a prominent group of inherited metabolic diseases involving accumulation of eponymous metabolites causing endogenous intoxication. For all three conditions, guidelines for diagnosis and management have been developed and revised over the last years, resulting in three revisions for GA1 and one revision for MMA/PA. The process of clinical guideline development in rare metabolic disorders is challenged by the scarcity and limited quality of evidence available. The body of literature is often fragmentary and where information is present, it is usually derived from small sample sizes. Therefore, the development of guidelines for GA1 and MMA/PA was initially confronted with a poor evidence foundation that hindered formulation of concrete recommendations in certain contexts, triggering specific research projects and initiation of longitudinal, prospective observational studies using patient registries. Reversely, these observational studies contributed to evaluate the value of newborn screening, phenotypic diversities, and treatment effects, thus significantly improving the quality of evidence and directly influencing formulation and evidence levels of guideline recommendations. Here, we present insights into interactions between guideline development and (pre)clinical research for GA1 and MMA/PA, and demonstrate how guidelines gradually improved from revision to revision. We describe how clinical studies help to unravel the relative impact of therapeutic interventions on outcome and conclude that despite new and better quality of research data over the last decades, significant shortcomings of evidence regarding prognosis and treatment remain. It appears that development of clinical guidelines can directly help to guide research, and vice versa.

Cellular and computational models reveal environmental and metabolic interactions in MMUT-type methylmalonic aciduria.

Methylmalonyl-coenzyme A (CoA) mutase (MMUT)-type methylmalonic aciduria is a rare inherited metabolic disease caused by the loss of function of the MMUT enzyme. Patients develop symptoms resembling those of primary mitochondrial disorders, but the underlying causes of mitochondrial dysfunction remain unclear. Here, we examined environmental and genetic interactions in MMUT deficiency using a combination of computational modeling and cellular models to decipher pathways interacting with MMUT. Immortalized fibroblast (hTERT BJ5ta) MMUT-KO (MUTKO) clones displayed a mild mitochondrial impairment in standard glucose-based medium, but they did not to show increased reliance on respiratory metabolism nor reduced growth or viability. Consistently, our modeling predicted MUTKO specific growth phenotypes only for lower extracellular glutamine concentrations. Indeed, two of three MMUT-deficient BJ5ta cell lines showed a reduced viability in glutamine-free medium. Further, growth on 183 different carbon and nitrogen substrates identified increased NADH (nicotinamide adenine dinucleotide) metabolism of BJ5ta and HEK293 MUTKO cells compared with controls on purine- and glutamine-based substrates. With this knowledge, our modeling predicted 13 reactions interacting with MMUT that potentiate an effect on growth, primarily those of secondary oxidation of propionyl-CoA, oxidative phosphorylation and oxygen diffusion. Of these, we validated 3-hydroxyisobutytyl-CoA hydrolase (HIBCH) in the secondary propionyl-CoA oxidation pathway. Altogether, these results suggest compensation for the loss of MMUT function by increasing anaplerosis through glutamine or by diverting flux away from MMUT through the secondary propionyl-CoA oxidation pathway, which may have therapeutic relevance.

A teenager with combined methylmalonic aciduria and homocystinuria (CblC type) presenting with neurological symptoms and congenital heart diseases: a case report.

Combined methylmalonic acidemia and homocystinuria, is a rare autosomal recessive disorder due to defective intracellular cobalamin metabolism. We report an 18-year-old Chinese male who presented with hypermyotonia, seizures, and congenital heart diseases. Mutation analysis revealed c.365A>T and c.482 G>A mutations in the MMACHC gene, diagnosed with methylmalonic aciduria and homocystinuria (CblC type). After treatment with vitamin B12, L-carnitine, betaine, and folate, which resulted in an improvement in his clinical symptoms and laboratory values. This case emphasizes that inborn errors of metabolism should be considered for a teenager presenting with challenging or neurologic symptoms, especially when combined with unexplained heart diseases.

Persistent moderate methylmalonic aciduria in a patient with methylmalonyl CoA epimerase deficiency.

BACKGROUND: Methylmalonyl CoA epimerase (MCE) deficiency was first reported in 2006 and only a few cases have been reported so far. The clinical spectrum of MCE deficiency ranges from asymptomatic to lifethreatening metabolic decompensation attacks. CASE: Herein we report a patient diagnosed with MCE deficiency with recurrent acute metabolic ketoacidosis attacks and moderate MMA-uria that persisted in periods without decompensation. At presentation, organic acid profiles were dominated by increased 3 hydroxybutyrate. CONCLUSIONS: 3-Oxothiolase deficiency as a main ketolysis defects disorder was initially suspected. However, the subsequently repeated organic acid analyses demonstrated mild and persistent elevation of methylmalonic acid. This report provides a new phenotype of the clinical and biochemical characterization of MCE deficiency.

Late-onset cblC deficiency around puberty: a retrospective study of the clinical characteristics, diagnosis, and treatment.

BACKGROUND: cblC deficiency is the most common type of methylmalonic aciduria in China. Late-onset patients present with various non-specific symptoms and are usually misdiagnosed. The purpose of this study is to investigate the clinical features of patients with late-onset cblC deficiency and explore diagnosis and management strategies around puberty. RESULTS: This study included 56 patients (35 males and 21 females) with late-onset cblC deficiency who were admitted to our clinic between 2002 and September 2021. The diagnosis was confirmed by metabolic and genetic tests. The clinical and biochemical features, disease triggers, outcome, and associated genetic variants were examined. The onset age ranged from 10 to 20 years (median age, 12 years). Fifteen patients (26.8%) presented with symptoms after infection or sports training. Further, 46 patients (82.1%) had neuropsychiatric diseases; 11 patients (19.6%), cardiovascular diseases; and 6 patients (10.7%), pulmonary hypertension. Renal damage was observed in 6 cases (10.7%). Genetic analysis revealed 21 variants of the MMACHC gene in the 56 patients. The top five common variants detected in 112 alleles were c.482G > A (36.6%), c.609G > A (16.1%), c.658_660delAAG (9.8%), c.80A > G (8.0%), and c.567dupT (6.3%). Thirty-nine patients carried the c.482G > A variant. Among 13 patients who exhibited spastic paraplegia as the main manifestation, 11 patients carried c.482G > A variants. Six patients who presented with psychotic disorders and spastic paraplegia had compound heterozygotic c.482G > A and other variants. All the patients showed improvement after metabolic treatment with cobalamin, L-carnitine, and betaine, and 30 school-aged patients returned to school. Two female patients got married and had healthy babies. CONCLUSIONS: Patients with late-onset cblC deficiency present with a wide variety of neuropsychiatric symptoms and other presentations, including multiple organ damage. As a result, cb1C deficiency can easily be misdiagnosed as other conditions. Metabolic and genetic studies are important for accurate diagnosis, and metabolic treatment with cobalamin, L-carnitine, and betaine appears to be beneficial.

Case report: Is exchange transfusion a possible treatment for metabolic decompensation in neonates with methylmalonic aciduria in the setting of limited resources?

Hyperammonemia is a serious complication of methylmalonic acidemia, with high mortality and permanent neurological sequelae in survivors. Primary hospitals are often the first admission hospitals for these children but are limited by their experience and facilities to provide rapid and effective treatment, increasing the risk of death in children with methylmalonic acidemia's metabolic crisis. In this report, we reported a case of a 7-day-old male neonate with decompensated methylmalonic acidemia, who underwent automatic peripheral arteriovenous exchange transfusion. The serum ammonia level of the boy decreased significantly post exchange transfusion. Therefore, we put forward the suggestion of exchange transfusion for hyperammonemia, in combination with medical therapy, in children with inborn errors of metabolism as an initial treatment option in primary hospitals if a rapid transfer to a center with dialysis facilities is not possible.

Caregiver burden, and parents' perception of disease severity determine health-related quality of life in paediatric patients with intoxication-type inborn errors of metabolism.

Background: Living with a non-acute (phenylketonuria) or acute (e.g. urea cycle disorders, organic acidurias) intoxication-type inborn error of metabolism (IT-IEM) can have a substantial impact on health-related quality of life (HrQoL) of paediatric patients and their families. Parents take primary responsibility for treatment monitoring and experience worry and fear about their child's health status. Quantitative evidence on parental psychological factors which may influence the HrQoL of patients with IT-IEM are sparse to non-existent. Methods: In this multicenter survey study 50 parents of IT-IEM patients (ages 5-19) assessed the severity of their child's disease, reported on caregiver burden, and proxy-rated their child's HrQoL. Additionally, 35 patient self-reports on HrQoL were obtained (n = 16 female patients, n = 19 male patients). Multiple linear regressions were conducted to examine the predictive power of child age, sex, medical diagnosis type (acute / non-acute), parental perceived disease severity and caregiver burden on patients' HrQoL. Mediation analyses were used to investigate the relation of caregiver burden and parental ratings of disease severity with patients' HrQoL. Results: Significant regression models for self-reported [F(5,34) = 10.752, p < .001, R 2 adj.. = 0.59] and parent proxy reported HrQoL [F(5,49) = 20.513, p < .001, R 2 adj.. = 0.67] emerged. High caregiver burden and perceived disease severity predicted significantly lower patient self- and proxy-reported HrQoL while type of diagnosis (acute versus non-acute) did not. Female sex predicted significantly lower self-reported HrQoL. High caregiver burden was the mediating factor between high perceived severity of the child's disease and lower proxy- by parent rated HrQoL. Conclusion: Detecting elevated burden of care and providing support for parents seems crucial to prevent adverse consequences for their children's HrQoL. Intervention studies are needed, to assess which support programs are most efficient.

Very long-term outcomes in 23 patients with cblA type methylmalonic acidemia.

OBJECTIVES: To present the very long-term follow up of patients with cobalamin A (cblA) deficiency. METHODS: A retrospective case series of adult (>16 years) patients with molecular or enzymatic diagnosis of cblA deficiency. RESULTS: We included 23 patients (mean age: 27 ± 7.6 years; mean follow-up: 24.9 ± 7.6 years). Disease onset was mostly pediatric (78% < 1 year, median = 4 months) with acute neurologic deterioration (65%). Eight patients presented with chronic symptoms, and one had an adult-onset mild cblA deficiency. Most of the patients (61%) were initially classified as vitamin B12-unresponsive methylmalonic aciduria (MMA); in vitro B12 responsiveness was subsequently found in all the tested patients (n = 13). Initial management consisted of protein restriction (57%), B12 (17%), or both (26%). The main long-term problems were intellectual disability (39%) and renal failure (30%). However, 56.5% of the patients were living independently. Intellectual disability was equally distributed among the initial treatment groups, while renal failure (moderate and beginning at the age of 38 years) was present in only one out of seven patients initially treated with B12. CONCLUSIONS: We provide a detailed picture of the long-term outcome of a series of adult cblA patients, mostly diagnosed before the enzymatic and molecular era. We confirm that about 35% of the patients do not present acutely, underlining the importance of measuring MMA in any case of unexplained chronic renal failure, intellectual disability, or growth delay. In addition, we describe a patient with a milder adult-onset form. Early B12 supplementation seems to protect from severe renal insufficiency.

Isolated psychiatric presentation of cobalamin C type disorder with novel mutation in middle childhood: A case report.

A 9-year-old boy presented with abnormal behavior for six months. He had unprovoked aggressive behavior, and occasional self-inflicting behavior. He also had decreased appetite, anhedonia, apathy, reduced sleep, low energy, motivation, and poor interaction with parents and peers. He had mild cognitive impairment, below-average intelligence, moderate depression, and mild psychotic symptoms on assessment with appropriate scales. He had macrocytic anemia with low vitamin B12 levels. Nextgeneration sequencing revealed a novel mutation of Leu116Pro of the MMACHC gene, suggestive of combined methylmalonic aciduria and homocystinuria (cblC type). Timely initiation of therapy can change the long-term neurological outcome.

Investigation on a MMACHC mutant from cblC disease: The c.394C>T variant.

The cblC disease is an inborn disorder of the vitamin B12 (cobalamin, Cbl) metabolism characterized by methylmalonic aciduria and homocystinuria. The clinical consequences of this disease are devastating and, even when early treated with current therapies, the affected children manifest symptoms involving vision, growth, and learning. The illness is caused by mutations in the gene codifying for MMACHC, a 282aa protein that transports and transforms the different Cbl forms. Here we present data on the structural properties of the truncated protein p.R132X resulting from the c.394C > T mutation that, along with c.271dupA and c.331C > T, is among the most common mutations in cblC. Although missing part of the Cbl binding domain, p.R132X is associated to late-onset symptoms and, therefore, it is supposed to retain residual function. However, to our knowledge structural-functional studies on c.394C > T mutant aimed at verifying this hypothesis are still lacking. By using a biophysical approach including Circular Dichroism, fluorescence, Small Angle X-ray Scattering, and Molecular Dynamics, we show that the mutant protein MMACHC-R132X retains secondary structure elements and remains compact in solution, partly preserving its binding affinity for Cbl. Insights on the fragile stability of MMACHC-R132X-Cbl are provided.

Epimutations in both the TESK2 and MMACHC promoters in the Epi-cblC inherited disorder of intracellular metabolism of vitamin B12.

BACKGROUND: epi-cblC is a recently discovered inherited disorder of intracellular vitamin B12 metabolism associating hematological, neurological, and cardiometabolic outcomes. It is produced by an epimutation at the promoter common to CCDC163P and MMACHC, which results from an aberrant antisense transcription due to splicing mutations in the antisense PRDX1 gene neighboring MMACHC. We studied whether the aberrant transcription produced a second epimutation by encompassing the CpG island of the TESK2 gene neighboring CCDC163P. METHODS: We unraveled the methylome architecture of the CCDC163P-MMACHC CpG island (CpG:33) and the TESK2 CpG island (CpG:51) of 17 epi-cblC cases. We performed an integrative analysis of the DNA methylome profiling, transcriptome reconstruction of RNA-sequencing (RNA-seq), chromatin immunoprecipitation sequencing (ChIP-Seq) of histone H3, and transcription expression of MMACHC and TESK2. RESULTS: The PRDX1 splice mutations and activation of numerous cryptic splice sites produced antisense readthrough transcripts encompassing the bidirectional MMACHC/CCDC163P promoter and the TESK2 promoter, resulting in the silencing of both the MMACHC and TESK2 genes through the deposition of SETD2-dependent H3K36me3 marks and the generation of epimutations in the CpG islands of the two promoters. CONCLUSIONS: The antisense readthrough transcription of the mutated PRDX1 produces an epigenetic silencing of MMACHC and TESK2. We propose using the term 'epi-digenism' to define this epigenetic disorder that affects two genes. Epi-cblC is an entity that differs from cblC. Indeed, the PRDX1 and TESK2 altered expressions are observed in epi-cblC but not in cblC, suggesting further evaluating the potential consequences on cancer risk and spermatogenesis.

The genotype analysis and prenatal genetic diagnosis among 244 pedigrees with methylmalonic aciduria in China.

OBJECTIVES: To investigate the phenotypes, biochemical features and genotypes for 244 pedigrees with methylmalonic aciduria (MMA) in China, and to perform the prenatal genetic diagnosis by chorionic villus for these pedigrees. MATERIALS AND METHODS: Gene analyses were performed for 244 pedigrees. There are 130 pedigrees, chorionic villus sampling was performed on the pregnant women to conduct the prenatal diagnosis. RESULTS: Among 244 patients, 168 (68.9%) cases were combined methylmalonic aciduria and homocystinuria, 76 (31.1%) cases were isolated methylmalonic aciduria. All the patients were diagnosed with MMA by their clinical manifestation, elevated blood propionylcarnitine, propionylcarnitine to acetylcarnitine ratio, and/or urine/blood methylmalonic acid with or without homocysteine. MMACHC, MMUT, SUCLG1 and LMBRD1 gene variants were found in 236 (96.7%) pedigrees included 6 probands with only one heterozygous variant out of 244 cases. For the 130 pedigrees who received a prenatal diagnosis, 22 fetuses were normal, 69 foetuses were carriers of heterozygous variants, and the remaining 39 foetuses harboured compound heterozygous variants or homozygous variants. The follow-up results were consistent with the prenatal diagnosis. CONCLUSION: The present study indicates genetic heterogeneity in MMA patients. Genetic analysis is a convenient method for prenatal diagnosis that will aid in avoiding the delivery of MMA patients.