Growth requirement for methionine in human melanoma-derived cell lines with different levels of MMACHC expression and methylation

Methionine dependence, the inability to grow in culture when methionine in the medium is replaced by its metabolic precursor homocysteine, occurs in many tumor cell lines. In most affected lines, the cause of methionine dependence is not known. An exception is the melanoma-derived cell line MeWo-LC1, in which hypermethylation of the MMACHC gene is associated with decreased MMACHC expression. Decreased expression results in decreased provision of the methylcobalamin cofactor required for activity of methionine synthase and thus decreased conversion of homocysteine to methionine. Analysis of data in the Cancer Cell Line Encyclopedia Archive demonstrated that MMACHC hypermethylation and decreased MMACHC expression occurred more frequently in melanoma cell lines when compared to other tumor cell lines. We further investigated methionine dependence and aspects of MMACHC function in a panel of six melanoma lines, including both melanoma lines with known methionine dependence status (MeWo, which is methionine independent, and A375, which is methionine dependent). We found that the previously unclassified melanoma lines HMCB, Colo829 and SH-4 were methionine dependent, while SK-Mel-28 was methionine independent. However, despite varying levels of MMACHC methylation and expression, none of the tested lines had decreased methylcobalamin and adenosylcobalamin synthesis as seen in MeWo-LC1, and the functions of both cobalamin-dependent enzymes methionine synthase and methylmalonyl-CoA mutase were intact. Thus, while melanoma lines were characterized by relatively high levels of MMACHC methylation and low expression, the defect in metabolism observed in MeWo-LC1 was unique, and decreased MMACHC expression was not a cause of methionine dependence in the other melanoma lines.

Multiomic analysis in fibroblasts of patients with inborn errors of cobalamin metabolism reveals concordance with clinical and metabolic variability

BACKGROUND

The high variability in clinical and metabolic presentations of inborn errors of cobalamin (cbl) metabolism (IECM), such as the cblC/epicblC types with combined deficits in methylmalonyl-coA mutase (MUT) and methionine synthase (MS), are not well understood. They could be explained by the impaired expression/activity of enzymes from other metabolic pathways.

METHODS

We performed metabolomic, genomic, proteomic, and post-translational modification (PTM) analyses in fibroblasts from three cblC cases and one epi-cblC case compared with three cblG cases with specific MS deficits and control fibroblasts.

FINDINGS

CblC patients had metabolic profilings consistent with altered urea cycle, glycine, and energy mitochondrial metabolism. Metabolomic analysis showed partial disruption and increased glutamate/ketoglutarate anaplerotic pathway of the tricarboxylic acid cycle (TCA), in patient fibroblasts. RNA-seq analysis showed decreased expression of MT-TT (mitochondrial tRNA threonine), MT-TP (mitochondrial tRNA proline), OXCT1 (succinyl CoA:3-oxoacid CoA transferase deficiency), and MT-CO1 (cytochrome C oxidase subunit 1). Proteomic changes were observed for key mitochondrial enzymes, including NADH:ubiquinone oxidoreductase subunit A8 (NDUFA8), carnitine palmitoyltransferase 2 (CPT2), and ubiquinol-cytochrome C reductase, complex III subunit X (UQCR10). Propionaldehyde addition in ornithine aminotransferase was the predominant PTM in cblC cells and could be related with the dramatic cellular increase in propionate and methylglyoxalate. It is consistent with the decreased concentration of ornithine reported in 3 cblC cases. Whether the changes detected after multi-omic analyses underlies clinical features in cblC and cblG types of IECM, such as peripheral and central neuropathy, cardiomyopathy, pulmonary hypertension, development delay, remains to be investigated.

INTERPRETATION

The omics-related effects of IECM on other enzymes and metabolic pathways are consistent with the diversity and variability of their age-related metabolic and clinical manifestations. PTMs are expected to produce cumulative effects, which could explain the influence of age on neurological manifestations.

FUNDING

French Agence Nationale de la Recherche (Projects PREDICTS and EpiGONE) and Inserm.

Late-onset cobalamin C deficiency type in adult with cognitive and behavioral disturbances and significant cortical atrophy and cerebellar damage in the MRI: a case report

Background

Late-onset cobalamin C (cblC) deficiency is associated with a wide range of neurological and psychiatric symptoms, hematological manifestations, anorexia, renal failure, ocular abnormalities, dermatitis, and pancreatitis. However, the neuroimaging characteristics of late-onset cblC deficiency remain insufficiently documented. Common findings include diffuse white matter swelling, varying degrees of severe leukoaraiosis, hydrocephalus, corpus callosum atrophy, and symmetric bilateral basal ganglia lesions. In this report, we present a case of late-onset cblC deficiency in adults presenting with cerebellar ataxia as the primary symptom. The MRI findings revealed bilateral lateral cerebellar hemispheres exhibiting symmetric hyperintensity, primarily observed in diffusion-weighted imaging (DWI), which is a rarely reported imaging change in this context.

Case presentation

Our patient was a male who experienced symptoms starting at the age of 30 years, including unsteady walking, apparent cerebellar ataxia, and cognitive impairment upon nervous system examination. Brain magnetic resonance imaging (MRI) exhibited symmetric hyperintensity in the bilateral lateral cerebellar hemispheres, predominantly manifested in DWI, without any enhancement. Subsequently, significantly elevated blood total homocysteine and urinary methylmalonic acid levels were observed. Genetic analysis confirmed the presence of MMACHC compound heterozygous mutants c.482G > A and c.609G > A, thus confirming the diagnosis of cblC deficiency. These variants were classified as likely pathogenic following the guidelines of the American College of Medical Genetics and Genomics (ACMG) and were verified using Sanger sequencing. Following treatment, the patient experienced improvements in walking ability and cognition, a significant decrease in blood total homocysteine levels, and reversal of the imaging lesions.

In conclusion

Late-onset cblC deficiency presents with diverse clinical and imaging manifestations. Early diagnosis and treatment are crucial in achieving a favorable prognosis. This case serves as a reminder to clinicians not to overlook genetic metabolic disorders, particularly those causing multisite damage, in adult patients with undiagnosed neurological disorders, especially those affecting the cerebellum. Notably, methylmalonic acidemia should be considered within the spectrum of bilateral cerebellar lesions.

Pulmonary fungal infection in a neonate with methylmalonic acidemia: A case report

BACKGROUND

Methylmalonic acidemia (MMA) is characterized by non-specific symptoms such as vomiting, and feeding difficulties, along with delayed mental and physical development. However, no case of MMA combined with pulmonary fungal infection has been reported yet.

CASE SUMMARY

We report the case of a neonate who presented pulmonary fungal infection along with the non-specific features of MMA. Exome sequencing revealed a c.331C>T variant in exon 3 of MMACHC from the father, and a c.658-c.660delAAG variant in exon 4 from the mother, which confirmed the diagnosis of cblC type MMA combined with hyperhomocysteinemia.

CONCLUSION

Invasive fungal infection might occur in some infants with MMA. Therefore, early diagnosis is recommended for unexplained pulmonary infection.

Clinical and Molecular Spectrum of Patients with Methylmalonic Acidemia

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.

Overexpression of MMACHC Prevents Craniofacial Phenotypes Caused by Knockdown of znf143b

ZNF143 is a sequence-specific DNA binding protein that regulates the expression of protein-coding genes and small RNA molecules. In humans, ZNF143 interacts with HCFC1, a transcriptional cofactor, to regulate the expression of downstream target genes, including MMACHC, which encodes an enzyme involved in cobalamin (cbl) metabolism. Mutations in HCFC1 or ZNF143 cause an inborn error of cobalamin metabolism characterized by abnormal cbl metabolism, intellectual disability, seizures, and mild to moderate craniofacial abnormalities. However, the mechanisms by which ZNF143 mutations cause individual phenotypes are not completely understood. Defects in metabolism and craniofacial development are hypothesized to occur because of decreased expression of MMACHC. But recent results have called into question this mechanism as the cause for craniofacial development. Therefore, in the present study, we implemented a loss of function analysis to begin to uncover the function of ZNF143 in craniofacial development using the developing zebrafish. The knockdown of znf143b, one zebrafish ortholog of ZNF143, caused craniofacial phenotypes of varied severity, which included a shortened and cleaved Meckel's cartilage, partial loss of ceratobranchial arches, and a distorted ceratohyal. These phenotypes did not result from a defect in the number of total chondrocytes but were associated with a mild to moderate decrease in mmachc expression. Interestingly, expression of human MMACHC via endogenous transgene prevented the onset of craniofacial phenotypes associated with znf143b knockdown. Collectively, our data establishes that knockdown of znf143b causes craniofacial phenotypes that can be alleviated by increased expression of MMACHC.

Abnormal chondrocyte development in a zebrafish model of cblC syndrome restored by an MMACHC cobalamin binding mutant

Variants in the MMACHC gene cause combined methylmalonic acidemia and homocystinuria cblC type, the most common inborn error of intracellular cobalamin (vitamin B12) metabolism. cblC is associated with neurodevelopmental, hematological, ocular, and biochemical abnormalities. In a subset of patients, mild craniofacial dysmorphia has also been described. Mouse models of Mmachc deletion are embryonic lethal but cause severe craniofacial phenotypes such as facial clefts. MMACHC encodes an enzyme required for cobalamin processing and variants in this gene result in the accumulation of two metabolites: methylmalonic acid (MMA) and homocysteine (HC). Interestingly, other inborn errors of cobalamin metabolism, such as cblX syndrome, are associated with mild facial phenotypes. However, the presence and severity of MMA and HC accumulation in cblX syndrome is not consistent with the presence or absence of facial phenotypes. Thus, the mechanisms by which mutations in MMACHC cause craniofacial defects are yet to be completely elucidated. Here we have characterized the craniofacial phenotypes in a zebrafish model of cblC (hg13) and performed restoration experiments with either a wildtype or a cobalamin binding deficient MMACHC protein. Homozygous mutants did not display gross morphological defects in facial development but did have abnormal chondrocyte nuclear organization and an increase in the average number of neighboring cell contacts, both phenotypes were fully penetrant. Abnormal chondrocyte nuclear organization was not associated with defects in the localization of neural crest specific markers, sox10 (RFP transgene) or barx1. Both nuclear angles and the number of neighboring cell contacts were fully restored by wildtype MMACHC and a cobalamin binding deficient variant of the MMACHC protein. Collectively, these data suggest that mutation of MMACHC causes mild to moderate craniofacial phenotypes that are independent of cobalamin binding.

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.

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.

Clinical, phenotypic and genetic landscape of case reports with genetically proven inherited disorders of vitamin B12 metabolism: A meta-analysis

Inherited disorders of B₁₂ metabolism produce a broad spectrum of manifestations, with limited knowledge of the influence of age and the function of related genes. We report a meta-analysis on 824 patients with a genetically proven diagnosis of an inherited disorder of vitamin B₁₂ metabolism. Gene clusters and age categories are associated with patients' manifestations. The "cytoplasmic transport" cluster is associated with neurological and ophthalmological manifestations, the "mitochondrion" cluster with hypotonia, acute metabolic decompensation, and death, and the "B₁₂ availability" and "remethylation" clusters with anemia and cytopenia. Hypotonia, EEG abnormalities, nystagmus, and strabismus are predominant in the younger patients, while neurological manifestations, such as walking difficulties, peripheral neuropathy, pyramidal syndrome, cerebral atrophy, psychiatric disorders, and thromboembolic manifestations, are predominant in the older patients. These results should prompt systematic checking of markers of vitamin B₁₂ status, including homocysteine and methylmalonic acid, when usual causes of these manifestations are discarded in adult patients.

Identification of MMACHC and ZEB2 mutations causing coexistent cobalamin C disease and Mowat-Wilson syndrome in a 2-year-old girl

Cobalamin C (cblC) disease and Mowat-Wilson syndrome (MWS) are rare hereditary diseases. To date, there have been no reports of people suffering from these two genetic diseases, or whether there is any correlation between the two diseases. We reported a 2-year-old girl with both cblC disease and MWS. The patient initially manifested as slow weight gain, hypotonia, broad nasal bridge, high forehead, high palate arch, ear crease, patent ductus arteriosus, atrial and ventricular septal defect and bilateral mild ventriculomegaly in the neonatal period. However, as the baby grew older, the typical facial features became more prominent, and overall developmental delays were noted at the subsequent follow-up, with the motor and cognitive development significantly lagging behind that of other children of the same age. At 26 days old, laboratory tests revealed remarkably elevated levels of serum homocysteine, C3/C2 and urine organic acid. Whole-exome sequencing detected compound heterozygous variants in MMACHC, including one previously reported mutation [c.609G > A (p.W203X) and a novel missense mutation[ c.643 T > C (p.Y215H)]. The computer simulations of the protein structure analysis of the novel missense mutation showed the variant p.Y215H replaced a neutral amino acid with a strongly basic lysine, which broken the local structure by changing the carbon chain skeleton and decreasing the interaction with adjacent amino acid. This is expected to damage the utilization of vitamin B12 and influence the synthesis of AdoCbl and MeCbl, contributing to its pathogenicity. Thus, clinical and genetic examinations confirmed the cblC disease. Another heterozygous variant in ZEB2 [NM_014795; loss1(exon:2-10)(all); 127901 bp] was detected by whole-exome sequencing. The heterozygous 3.04 Mb deletion in EB2 [GRCH37]del(2)(q22.2q22.3) (chr2:142237964-145274917) was also confirmed by genome-wide copy number variations (CNVs) scan, which was pathogenic and led to the diagnosis of Mowat-Wilson syndrome. The biochemical indicators associated with cblC disease in the patient were well controlled after treatment with vitamin B12 and betaine. Here, a patient with coexisting cblC disease and MWS caused by different pathogenic genes was reported, which enriched the clinical research on these two rare genetic diseases.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01271-1.

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.

Case Report: A Rare Case of Thrombotic Microangiopathy Induced by Remethylation Disorders

In this research, we described a very rare case of thrombotic microangiopathy induced by remethylation disorders. A 16-year-old boy presented to the emergency department with 5 months of weakness and fatigue. He was diagnosed with thrombotic microangiopathy based on clinical manifestation and laboratory information, which showed microangiopathic hemolytic anemia, renal impairment, and thrombocytopenia. After a complex diagnostic workup, the metabolite screening parameters and sequencing results guided us toward the diagnosis of remethylation disorders. The patient was diagnosed with thrombotic microangiopathy induced by remethylation disorders (cblC).

Intracellular processing of vitamin B12 by MMACHC (CblC)

Vitamin B₁₂ (cobalamin, Cbl, B₁₂) is a water-soluble micronutrient synthesized exclusively by a group of microorganisms. Human beings are unable to make B₁₂ and thus obtain the vitamin via intake of animal products, fermented plant-based foods or supplements. Vitamin B₁₂ obtained from the diet comprises three major chemical forms, namely hydroxocobalamin (HOCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl). The most common form of B₁₂ present in supplements is cyanocobalamin (CNCbl). Yet, these chemical forms cannot be utilized directly as they come, but instead, they undergo chemical processing by the MMACHC protein, also known as CblC. Processing of dietary B₁₂ by CblC involves removal of the upper-axial ligand (beta-ligand) yielding the one-electron reduced intermediate cob(II)alamin. Newly formed cob(II)alamin undergoes trafficking and delivery to the two B₁₂-dependent enzymes, cytosolic methionine synthase (MS) and mitochondrial methylmalonyl-CoA mutase (MUT). The catalytic cycles of MS and MUT incorporate cob(II)alamin as a precursor to regenerate the coenzyme forms MeCbl and AdoCbl, respectively. Mutations and epimutations in the MMACHC gene result in cblC disease, the most common inborn error of B₁₂ metabolism, which manifests with combined homocystinuria and methylmalonic aciduria. Elevation of metabolites homocysteine and methylmalonic acid occurs because the lack of an active CblC blocks formation of the indispensable precursor cob(II)alamin that is necessary to activate MS and MUT. Thus, in patients with cblC disease, vitamin B₁₂ is absorbed and present in circulation in normal to high concentrations, yet, cells are unable to make use of it. Mutations in seemingly unrelated genes that modify MMACHC gene expression also result in clinical phenotypes that resemble cblC disease. We review current knowledge on structural and functional aspects of intracellular processing of vitamin B₁₂ by the versatile protein CblC, its partners and possible regulators.

Clinical and biochemical outcomes in cobalamin C deficiency with use of high-dose hydroxocobalamin in the early neonatal period

This case report describes a patient with early-onset cobalamin C deficiency who was started on treatment with high-dose parenteral hydroxocobalamin after diagnosis at 13 days of life. Prior to diagnosis, initial presenting symptoms included poor feeding, lethargy, apneic episodes, hypothermia, and hypotonia; these symptoms resolved after initiation of medication. Methylmalonic acid and homocysteine levels were trended and significantly improved with treatment. She was maintained on 2 mg/kg/day dosing of hydroxocobalamin. No adverse effects to treatment were observed. At the time of this report, the patient was 19 months of age; she had not manifested common findings of early-onset cobalamin C deficiency, including microcephaly, poor feeding, growth abnormalities, hypotonia, seizures, maculopathy, or neurodevelopmental delay. This report suggests that early initiation of high-dose hydroxocobalamin is safe and effective.

Combined Methylmalonic Aciduria and Homocystinuria Presenting as Pulmonary Hypertension

Combined methylmalonic aciduria and homocystinuria, cblC type, (MAHCC) is a rare autosomal recessive metabolic disorder of remethylation caused due to mutations in the MMACHC (metabolism of cobalamin associated C) gene with predominant neurological involvement. Microvascular, renal, and cardiovascular complications are also known to occur. However, the disease presenting primarily with a cardiovascular phenotype without any neurological involvement is a rare entity. We report a case of developmentally normal 23-mo-old female child, who presented with pulmonary arterial hypertension (PAH) and succumbed to cardiac failure. Extensive workup for PAH was inconclusive. Posthumous trio whole-exome sequencing revealed pathogenic compound heterozygous variants in the MMACHC. Diagnosis of MAHCC should be considered as a differential diagnosis for unexplained PAH in children. An elevated plasma homocysteine level can serve as a simple screening modality for this disorder. Accurate diagnosis has paramount therapeutic implications, as management with hydroxocobalamin and betaine may lead to partial or complete remission of PAH in these patients.

Preimplantation Genetic Testing for Rare Inherited Disease of MMA-CblC: an Unaffected Live Birth

Methylmalonic acidemia combined with homocysteinemia and cobalamin C type (MMA-CblC, MIM # 277400) is a rare inherited disease with cobalamin metabolic disorder, which are caused by deficiency in the MMACHC gene. A couple with a proband child carried with compound heterozygous mutations of MMACHC (c.609G>A and c.567 dup T, NM_015506) sought for assisted reproductive technology to avoid the transmission of pathogenic genetic variants and unnecessary induction of labor. Thus, in vitro fertilization (IVF), preimplantation genetic testing (PGT), and prenatal genetic diagnosis were applied to fulfill this clinical demand. In this study, seven embryos were biopsied and carried out whole-genome amplification using multiple annealing and looping-based amplification cycle (MALBAC) method. Sanger sequencing together with copy number variation (CNV) analysis and single-nucleotide polymorphism (SNP) haplotyping was conducted to detect the mutated alleles and chromosomal abnormalities simultaneously. Three embryos (E07, E06, and E02) were confirmed without CNVs and inherited mutations at MMACHC gene. Embryo E07 with the best embryo ranking of 5BB was selected preferentially to transfer which led to a successful pregnancy and an unaffected live birth. Prenatal genetic diagnosing with amniotic fluid cells, Sanger sequencing with cord blood cells, and neonate MMA screening further verified our successful application of PGT in preventing mutated allele transmission for this rare inherited disease.

Epimutation of MMACHC compound to a genetic mutation in cblC cases

Background

Methylmalonic aciduria (MMA) combined with homocystinuria, cobalamin(cbl)C deficiency type (OMIM 277400), is the most common autosomal recessive inherited disorder of intracellular cobalamin metabolism caused by mutations in the MMACHC gene (OMIM 609831), of which more than 100 mutations have been identified to date. In this study, we only identified a coding mutation in one allele at the MMACHC gene locus, and no large fragments deletion or duplication were found. Up to now, only three epimutation cblC cases were reported. We hypothesized whether the MMACHC was hypermethylated.

Methods

To address this hypothesis, the entire coding region and adjacent splice sites of the panel genes involved in metabolic diseases were sequenced using the Illumina HiSeq X platform, followed by confirmation via Sanger sequencing in their parents and brothers. Methylation analysis of the MMACHC was performed using an EpiTect Bisulfite Kit and methylation‐specific PCR (MSP) to investigate the role of epimutations in cblC disease.

Results

We identified a clearly pathogenic single heterozygous c.658_660del, p. (K220del) mutation, which was also identified in the mother. Analysis of the MMACHC indicated a heterozygous epimutation consisting of 34 hypermethylated CpG sites in a CpG island encompassing the promoter and first exon of the MMACHC, which was also identified in the father. Furthermore, we identified a single heterozygous c.*2C>T mutation in the sixth exon of the PRDX1 (OMIM 176763) in patients and their fathers, which was the only sequence variation that segregated with the MMACHC methylation. Neither c.658_660del and epimutation in MMACHC nor c.*2C>T in PRDX1 was discovered in her brother.

Conclusion

We report compound heterozygotes in MMACHC for a genetic mutation and an epimutation in cblC cases. To our best knowledge, this is the first report of two cblC cases from China caused by compound heterozygous mutations with a coding mutation in one allele and an epimutation in the other at the MMACHC locus.

Methionine dependence in tumor cells: The potential role of cobalamin and MMACHC

Methionine dependence of tumor cell lines, the inability to grow in tissue culture media lacking methionine but supplemented with homocysteine, has been known for decades, but an understanding of the mechanism underlying this phenomenon remains incomplete. Methionine dependence of certain glioma and melanoma cell lines has been linked to alterations in the metabolism of cobalamin (vitamin B₁₂). In the MeWo LC1 melanoma line, complementation analysis demonstrated that the genetic defect affected the same locus mutated in the cblC inborn error of cobalamin metabolism; hypermethylation of the MMACHC promoter was subsequently demonstrated. Analysis of data in the Cancer Cell Line Encyclopedia showed increased MMACHC methylation levels in melanoma lines compared to other types of cancer. RNA sequencing data from isolated tumors, tabulated at the cBioPortal for Cancer Genomics website, showed decreased MMACHC expression compared to other tumors; and methylation data tabulated at the TGGA Wanderer website demonstrated increased MMACHC methylation. These data suggest that disruptions in cobalamin metabolism might play a more general role in methionine dependence, and potentially in the pathogenesis of melanoma cell lines and primary tumors.

Identification of MMACHC and PROKR2 mutations causing coexistent cobalamin C disease and Kallmann syndrome in a young woman

Cobalamin C (cblC) disease and Kallmann syndrome (KS) are rare hereditary diseases. To date, no report has described the coexistence of those two genetic disorders in the same patient, or an association between them. We report the case of a 23-year-old woman with cblC defect and KS. She first presented mild memory problems in puberty, which worsened in adulthood to progressive memory loss accompanied by slow and unsteady walking, slow response, inattention, cognitive impairment, insomnia, no sense of smell, and the lack of spontaneous puberty. Laboratory tests revealed gonadotropin deficiency, a low estrogen level, and remarkably elevated serum homocysteine and serum and urine organic acid levels. Whole-exome sequencing detected compound heterozygous variants in MMACHC [c.398_399del (p.Gln133Argfs*4) and c.482G > A (p.Arg161Gln)] and heterozygous variants in PROKR2 [c.337T > C (p.Tyr113His)]. Thus, clinical and genetic examinations confirmed the cblC disease and KS diagnoses. This report on coexisting cblC disease and KS caused by different pathogenic genes in a single patient enriches the clinical research on these two rare genetic diseases.

A high frequency and geographical distribution of MMACHC R132* mutation in children with cobalamin C defect

Cobalamin C defect is caused by pathogenic variants in the MMACHC gene leading to impaired conversion of dietary vitamin B₁₂ into methylcobalamin and adenosylcobalamin. Variants in the MMACHC gene cause accumulation of methylmalonic acid and homocysteine along with decreased methionine synthesis. The spectrum of MMACHC gene variants differs in various populations. A total of 19 North Indian children (age 0-18 years) with elevated methylmalonic acid and homocysteine were included in the study, and their DNA samples were subjected to Sanger sequencing of coding exons with flanking intronic regions of MMACHC gene. The genetic analysis resulted in the identification of a common pathogenic nonsense mutation, c.394C > T (R132*) in 85.7% of the unrelated cases with suspected cobalamin C defect. Two other known mutations c.347T > C (7%) and c.316G > A were also detected. Plasma homocysteine was significantly elevated (> 100 µmol/L) in 75% of the cases and methionine was decreased in 81% of the cases. Propionyl (C3)-carnitine, the primary marker for cobalamin C defect, was found to be elevated in only 43.75% of cases. However, the secondary markers such as C3/C2 and C3/C16 ratios were elevated in 87.5% and 100% of the cases, respectively. Neurological manifestations were the most common in our cohort. Our findings of the high frequency of a single MMACHC R132* mutation in cases with combined homocystinuria and methylmalonic aciduria may be proven helpful in designing a cost-effective and time-saving diagnostic strategy for resource-constraint settings. Since the R132* mutation is located near the last exon-exon junction, this is a potential target for the read-through therapeutics.

Thiolatocobalamins repair the activity of pathogenic variants of the human cobalamin processing enzyme CblC

Thiolatocobalamins are a class of cobalamins comprised of naturally occurring and synthetic ligands. Glutathionylcobalamin (GSCbl) occurs naturally in mammalian cells, and also as an intermediate in the glutathione-dependent dealkylation of methylcobalamin (MeCbl) to form cob(I)alamin by pure recombinant CblC from C. elegans. Glutathione-driven deglutathionylation of GSCbl was demonstrated both in mammalian as well as in C. elegans CblC. Dethiolation is orders of magnitude faster than dealkylation of Co-C bonded cobalamins, which motivated us to investigate two synthetic thiolatocobalamins as substrates to repair the enzymatic activity of pathogenic CblC variants in humans. We report the synthesis and kinetic characterization of cysteaminylcobalamin (CyaCbl) and 2-mercaptopropionylglycinocobalamin (MpgCbl). Both CyaCbl and MpgCbl were obtained in high purity (90-95%) and yield (78-85%). UV-visible spectral properties agreed with those reported for other thiolatocobalamins with absorbance maxima observed at 372 nm and 532 nm. Both CyaCbl and MpgCbl bound to wild type human recombinant CblC inducing spectral blue-shifts characteristic of the respective base-on to base-off transitions. Addition of excess glutathione (GSH) resulted in rapid elimination of the β-ligand to give aquacobalamin (H₂OCbl) as the reaction product under aerobic conditions. Further, CyaCbl and MpgCbl underwent spontaneous dethiolation thereby repairing the loss of activity of pathogenic variants of human CblC, namely R161G and R161Q. We posit that thiolatocobalamins could be exploited therapeutically for the treatment of inborn errors of metabolism that impair processing of dietary and supplemental cobalamin forms. While these disorders are targets for newborn screening in some countries, there is currently no effective treatment available to patients.

Adolescent/adult-onset homocysteine remethylation disorders characterized by gait disturbance with/without psychiatric symptoms and cognitive decline: a series of seven cases

Homocysteine remethylation disorders are rare inherited disorders caused by a deficient activity of the enzymes involved in the remethylation of homocysteine to methionine. The adolescent/adult-onset remethylation disorders are rarely reported. We analyzed the clinical and genetic characteristics of seven cases with adolescent/adult remethylation disorders, including 5 cases of the cobalamin C disease (cblC) and 2 cases of the methylenetetrahydrofolate reductase deficiency. The average onset age was 21.1 (range 14 to 40) years. All patients complained of gait disturbances. Other common symptoms included psychiatric symptoms (5/7) and cognitive decline (4/7). Acute encephalopathy, dysarthria, anorexia, vomiting, ketoacidosis, anemia, cataract, and hand tremor were also observed. The mean total homocysteine in serum when the patients were diagnosed was 94.6 (range 53.1-154.5) mol/L. Electrophysiological studies revealed neuropathy in the lower limbs (6/7). The brain MRI showed reversible altered signal from the dorsal portions of the cerebellar hemispheres (1/7), periventricular hyperintensity (2/7), and delayed/impaired myelination (2/7). The sural nerve biopsy performed in one case showed a modest loss of myelinated fibers. Five patients showed heterozygous mutations of the MMACHC gene, including c.482G>A (5/5), c.609G>A (2/5), and c.658-660delAAG (3/5). Two patients showed heterozygous mutations of the MTHFR gene, including c.698C>A (2/2), c.698C>G (1/2), and c.236+1G>A (1/2). The patients responded well to the treatments with significant improvements. Adolescent/adult-onset remethylation disorders are easily misdiagnosed. We recommend testing the serum homocysteine concentrations in young/adult patients with unexplained neuro-psychotic symptoms. Furthermore, individuals with significantly elevated serum homocysteine concentrations should be further tested by organic acid screening and genetic analysis.

The human B12 trafficking protein CblC processes nitrocobalamin

In humans, cobalamin or vitamin B₁₂ is delivered to two target enzymes via a complex intracellular trafficking pathway comprising transporters and chaperones. CblC (or MMACHC) is a processing chaperone that catalyzes an early step in this trafficking pathway. CblC removes the upper axial ligand of cobalamin derivatives, forming an intermediate in the pathway that is subsequently converted to the active cofactor derivatives. Mutations in the cblC gene lead to methylmalonic aciduria and homocystinuria. Here, we report that nitrosylcobalamin (NOCbl), which was developed as an antiproliferative reagent, and is purported to cause cell death by virtue of releasing nitric oxide, is highly unstable in air and is rapidly oxidized to nitrocobalamin (NO₂Cbl). We demonstrate that CblC catalyzes the GSH-dependent denitration of NO₂Cbl forming 5-coordinate cob(II)alamin, which had one of two fates. It could be oxidized to aquo-cob(III)alamin or enter a futile thiol oxidase cycle forming GSH disulfide. Arg-161 in the active site of CblC suppressed the NO₂Cbl-dependent thiol oxidase activity, whereas the disease-associated R161G variant stabilized cob(II)alamin and promoted futile cycling. We also report that CblC exhibits nitrite reductase activity, converting cob(I)alamin and nitrite to NOCbl. Finally, the denitration activity of CblC supported cell proliferation in the presence of NO₂Cbl, which can serve as a cobalamin source. The newly described nitrite reductase and denitration activities of CblC extend its catalytic versatility, adding to its known decyanation and dealkylation activities. In summary, upon exposure to air, NOCbl is rapidly converted to NO₂Cbl, which is a substrate for the B₁₂ trafficking enzyme CblC.

Rapid screening of MMACHC gene mutations by high-resolution melting curve analysis

Background

Cobalamin (cbl) C is a treatable rare hereditary disorder of cbl metabolism with autosomal recessive inheritance. It is the most common organic acidemia, manifested as methylmalonic academia combined with homocysteinemia. Early screening and diagnosis are important. The mutation spectrum of the MMACHC gene causing cblC varies among populations. The mutation spectrum in Chinese population is notably different from that in other populations.

Methods

A PCR followed by high‐resolution melting curve analysis (PCR‐HRM) method covering all coding exons of MMACHC gene was designed to verify 14 pathogenic MMACHC gene variants found in patients with cblC, including all common mutations in Chinese patients with cblC.

Result

By PCR‐HRM analysis, 14 pathogenic variants of MMACHC showed distinctly different melting curves, which were consistent with Sanger sequencing. The homozygous type of the most common mutation c.609G > A (p.Trp203Ter) can also be analyzed by specially designed PCR‐HRM.

Conclusion

The established PCR‐HRM method for screening common pathogenic MMACHC variants in Chinese patients with cblC has the advantages of high accuracy, high throughput, low cost, and high speed. It is suitable for the large‐sample screening of suspected children with methylmalonic acidemia and carriers in population.

Multiple sclerosis and intracellular cobalamin defect (MMACHC/PRDX1) comorbidity in a young male

Background

Methylmalonic acidaemia with homocystinuria type C (cblC defect) is an inherited error of cobalamin metabolism. Cobalamin deficient processing results in high levels of methylmalonic acid and homocysteine. The latter is considered to be a risk factor for multiple sclerosis (MS). We report on the first case of a patient with comorbid cblC defect and MS.

Case report

This young male presented at the age of 14 with a relapsing-remitting neurological disorder associated with imaging alterations suggestive of MS. Treatment resulted in a partial clinical improvement with vanishing of white matter lesions. Later on, the emergence of unexpected clinical features led to a metabolic work-up, revealing a cobalamin intracellular defect. Genetic analysis disclosed a single variant in MMACHC (c.482G > A; p.Arg161Gln) and another splicing variant in PRDX1 (c.1-515G > T) that cause the silencing of the wild-type MMACHC allele, so confirming the diagnosis of cblC defect. Although cblC treatment was effective, when 17-year-old he experienced a relapse of neurological symptoms. Further imaging and laboratory studies eventually supported the diagnosis of MS.

Discussion

While the comorbid association of MS and cblC in our patient may remain anecdotic, we suggest measuring Hcy and MMA levels in young patients with a relapsing-remitting demyelinating disorder, in order not to miss a cblC defect, that requires a specific and effective treatment.

High-dose hydroxocobalamin achieves biochemical correction and improvement of neuropsychiatric deficits in adults with late onset cobalamin C deficiency

Cobalamin C (cblC) deficiency is the most common inborn error of intracellular cobalamin metabolism caused by pathogenic variant(s) in MMACHC and manifests with methylmalonic acidemia, hyperhomocysteinemia, and hypomethioninemia with a variable age of presentation. Individuals with late‐onset cblC may be asymptomatic until manifesting neuropsychiatric symptoms, thromboembolic events, and renal disease. Although hydroxocobalamin provides a foundation for therapy, optimal dose regimen for adult patients has not been systematically evaluated. We report three adult siblings with late‐onset cblC disease, and their biochemical and clinical responses to high‐dose hydroxocobalamin. The 28‐year‐old proband presented with severe psychosis, progressive neurological deterioration, and deep venous thrombosis complicated by a pulmonary embolism. MRI studies identified lesions in the spinal cord, periventricular white matter, and basal ganglia. Serum homocysteine and methylmalonic acid levels were markedly elevated. Hydroxocobalamin at standard dose (1 mg/day) initially resulted in partial metabolic correction. A regimen of high‐dose hydroxocobalamin (25 mg/day) together with betaine and folic acid resulted in rapid and sustainable biochemical correction, resolution of psychosis, improvement of neurological functions, and amelioration of brain and spinal cord lesions. Two siblings who did not manifest neuropsychiatric symptoms or thromboembolism achieved a satisfactory metabolic control with the same high‐dose regimen. Hydroxocobalamin injection was then spaced out to 25 mg weekly with good and sustainable metabolic control. All three patients are compound heterozygotes for c.271dupA p.Arg91LysfsX14 and c.389A > G p.Tyr130Cys. This study highlights the importance of evaluating intracellular cobalamin metabolism in adults with neuropsychiatric manifestations and/or thromboembolic events, and demonstrates that high‐dose hydroxocobalamin achieves rapid and sustainable metabolic control and improvement in neuropsychiatric outcomes in adults with late‐onset cblC disease.

Hydrocephalus in cblC type methylmalonic acidemia

Methylmalonic acidemia (MMA) is a typical type of organic acidemia caused by defects in methylmalonyl-CoA mutase or adenosyl-cobalamin synthesis. Hydrocephalus (HC), results from an imbalance between production and absorption of cerebrospinal fluid (CSF), causeing enlarged cerebral ventricles and increased intracranial pressure, is a condition that requires urgent clinical decision-making. MMA without treatment could result in brain damage. However, HC in MMA was rarely reported. In this study, 147 MMA were identified from 9117 high risk children by gas chromatography mass spectrometry (GC/MS) for organic acidurias screening in urine samples and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for amino acids detection in blood samples. Totally 10 cases with MMA and HC were determined by brain MRI/CT, as well as gene mutation testing either by high throughput sequencing or Sanger sequencing. Besides, homocysteine was also analyzed for the 10 MMA with HC. Out of them, 9 cases carry out compound heterozygous mutations or homozygous mutation in MMACHC gene, and 1 case has MUTmutation. The mutation c.609G > A in MMACHC was the most common in the cbl type patients. Although MMA has a high incidence in Shandong province of China, especially cblC type. All of the 10 patients were not correctly diagnosed before developing HC. As a result, when a child develops progressive and refractory HC, the screening for inherited metabolic diseases should be immediately conducted.

Mutation analysis of genes related to methylmalonic acidemia: identification of eight novel mutations

Methylmalonic acidemia (MMA), an inherited metabolic disease, results from genetic defects in methylmalonyl-CoA mutase or any of the proteins involved in adenosylcobalamin synthesis. This enzyme is classified into several complementation groups and genotypic classes. In this work we explain the biochemical, structural and genetic analysis of 25 MMA patients, from Iran. The diagnosis was established by the measurement of propionylcarnitine in blood using tandem mass spectrometry and confirmed using a gas chromatography-flame ionization detector. Using clinical, biochemical, structural and molecular analyses we identified 15 mut MMA, three cblA, one cblB, and four cblC-deficient patients. Among mutations identified in the MUT gene (MUT) only one, the c.1874A>C (p.D625A) variant, is likely a mut^- mutation. The remaining mutations are probably mut⁰. Here, we present the first molecular analysis of MMA in Iranian patients and have identified eight novel mutations. Four novel mutations (p.D625A, p.R326G, p.V157F, p.F379L) were seen exclusively in patients from northern Iran. One novel splice site mutation (c.2125-3C>G) in MUT and two novel mutation (p.N225M and p.A99P) in the MMAA gene were associated with patients from eastern Iran. The rs184829210 SNP was recognized only in patients with the novel c.958G>A (p.A320T) mutation. This study confirms pathogenesis of deficient enzyme activity in MUT, MMAA, MMAB, and MMACHC as previous observations. These results could act as a basis for the performance of pharmacological therapies for increasing the activity of proteins derived from these mutations.

Newborn Screening for Methylmalonic Acidemia in a Chinese Population: Molecular Genetic Confirmation and Genotype Phenotype Correlations

Background: Methylmalonic acidemia (MMA) incidence was evaluated based on newborn screening in Xuzhou from November 2015 to December 2017, and the clinical, biochemical and molecular characteristics of patients with MMA harboring MMACHC and MUT mutations were summarized. Methods: During the study, 236,368 newborns were screened for MMA by tandem mass spectrometry (MS/MS) in the Maternity and Child Health Care Hospital of Xuzhou. C3, C3/C2 and methionine, and tHcy if necessary, were measured during the first screening. Blood samples from the infants and/or their family members were used for DNA analysis. The entire coding regions of the MMACHC and MUT genes associated with MMA were sequenced by DNA MassARRAY and next-generation sequencing (NGS). Results: Eleven patients with MMACHC mutations and three with MUT mutations were identified among the 236,368 screened newborns; the estimated total incidence of MMA was 1:16,883. Among the MMA patients, two died of infection-triggered metabolic crisis approximately 3 months after birth. All the patients identified had two mutant alleles except for one individual with early-onset disease. The most common MMACHC mutation was c.609G > A. The laboratory levels of C3 and C3/C2 were elevated in MMA individuals compared to other infants. Importantly, we demonstrate that accelerated C2 degradation is related to air temperature and humidity. Conclusion: Our study reports the clinical characteristics of MMA and diagnosis through MS/MS and NGS. There was a higher incidence of MMA with homocysteinemia than of isolated MMA in Xuzhou. Insight from this study may help explain the high false-positive rate of MMA in summer.

Molecular genetic characterization of cblC defects in 126 pedigrees and prenatal genetic diagnosis of pedigrees with combined methylmalonic aciduria and homocystinuria

Background

We sought to analyse MMACHC variants among 126 pedigrees with cobalamin (cbl) C deficiency and combined methylmalonic aciduria and homocystinuria by Sanger sequencing, characterize the spectrum of MMACHC gene variants, and perform prenatal genetic diagnosis by chorionic villus sampling among these pedigrees.

Methods

Peripheral blood was collected from 126 probands and their parents who visited the Genetic Counseling Clinic at our hospital between January 2014 and December 2017, and DNA was extracted from the blood. Then, we amplified the coding sequence and splicing regions of the MMACHC gene by PCR, and the PCR products were further sequenced to detect the variants in each pedigree. In 62 families, pregnant women were subjected to chorionic villus sampling for prenatal genetic diagnosis.

Results

In total, 31 distinct variants were detected in the 126 pedigrees, and the most frequent variants were c.609G > A (p.Trp203Ter), c.658_660delAAG (p.Lys220del), c.567dupT (p.Ile190Tyrfs*13) and c.80A > G (p.Gln27Arg). Two of these variants have not been previously reported in the literature. One variant [c.463_465delGGG (p.Gly155del)] is a small-scale deletion, and the other variant [c.637G>T(p.Glu213Ter)] is a nonsense mutation. Among the 62 pedigrees who received a prenatal diagnosis, 16 foetuses were normal, 34 foetuses were carriers of heterozygous variants, and the remaining 12 foetuses harboured compound heterozygous variants or homozygous variants. Couples whose foetuses were normal or carriers continued the pregnancy, whereas couples whose foetuses harboured compound heterozygous variants or homozygous variants decided to terminate the pregnancy. The follow-up results were consistent with the prenatal diagnosis.

Conclusions

Two novel MMACHC variants were identified, and prenatal genetic diagnosis is an accurate and convenient method that helps avoid the delivery of combined methylmalonic aciduria and homocystinuria patients.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0666-x) contains supplementary material, which is available to authorized users.

Clinical presentation, gene analysis and outcomes in young patients with early-treated combined methylmalonic acidemia and homocysteinemia (cblC type) in Shandong province, China

OBJECTIVES

To estimate the incidence of MMA on newborn screening in Shandong province from May 2011 to May 2014 and summarize the clinical presentation, biochemical features, mutation analysis, and treatment regime of early-treated patients with cblC disease.

METHODS

Between May 2011 and May 2014, 35,291 newborns were screened for MMA in Jinan maternal and Child Care Hospital, Shandong province. The levels of C3, C3/C2, methionine and tHcy were measured. Most patients received treatment with intramuscular hydroxocobalamin after diagnosis. Metabolic parameters, clinical presentation and mental development were followed up.

RESULTS

Nine patients were identified among 35,291 by newborn screening, giving an estimated incidence of 1:3920 live births for MMA, and all were classified as cblC disease. Among them, five patients received treatment with intramuscular hydroxocobalamin and two patients did not receive any treatment. One patient died of metabolic crises triggered by infection at the age of 38 days. Seven different mutations (c.609G>A, c.455_457delCCC, c.394C>T, c.445_446insA, c.658_660delAAG, c.452A>G and IVS1+1G>A) were detected. The mutations (c.455_457delCCC and IVS1+1G>A) are novel. Five patients who received treatment had favorable metabolic response, with both reduction of urine MMA and tHcy and increase of methionine. We obtained 7 records of DQ assessment. The five patients who received treatment presented with developmental delay and obvious neurological manifestations. In two patients who did not receive any treatment, case 8 presented with severe mental retardation and developmental delay, while case 9 had nearly normal DQ values at the age of 1(1/12)years.

CONCLUSION

Our study characterized variable phenotypes of neurodevelopment in early-treated cblC patients diagnosed on newborn screening. The long-term outcomes of cblC disease are unsatisfactory in spite of conventional treatment and improvement of biochemical abnormalities. Although the number of patients is too small, the information provided in this work is of value in highlighting possible genotype-phenotype correlation that influences outcomes in cblC disease by future studies.

MMACHC gene mutation in familial hypogonadism with neurological symptoms

Recent studies have convincingly documented that hypogonadism is a component of various hereditary disorders and is often recognized as an important clinical feature in combination with various neurological symptoms, yet, the causative genes in a few related families are still unknown. High-throughput sequencing has become an efficient method to identify causative genes in related complex hereditary disorders. In this study, we performed exome sequencing in a family presenting hypergonadotropic hypogonadism with neurological presentations of mental retardation, epilepsy, ataxia, and leukodystrophy. After bioinformatic analysis and Sanger sequencing validation, we identified compound heterozygous mutations: c.482G>A (p.R161Q) and c.609G>A (p.W203X) in MMACHC gene in this pedigree. MMACHC was previously confirmed to be responsible for methylmalonic aciduria (MMA) combined with homocystinuria, cblC type (cblC disease), a hereditary vitamin B12 metabolic disorder. Biochemical and gas chromatography-mass spectrometry (GC-MS) examinations in this pedigree further supported the cblC disease diagnosis. These results indicated that hypergonadotropic hypogonadism may be a novel clinical manifestation of cblC disease, but more reports on additional patients are needed to support this hypothesis.

Genetic analysis of four cases of methylmalonic aciduria and homocystinuria, cblC type#

Methylmalonic aciduria and homocystinuria, cblC type, is the most common disorder of intracellular vitamin B12 (cobalamin, cbl) metabolism, which results in impaired biosynthesis of methylcobalamin and adenosylcobalamin. The gene MMACHC responsible for the cblC type had been identified, which enables molecular diagnostics. Here, we report four cblC type cases, which were identified by the typical manifestations, and a new approach of next-generation sequencing platform in pediatrics for genetic diseases, further confirmed by Sanger sequencing of the whole MMACHC gene. The article will replenish the mutational information of related genes to the cblC type, which makes for detecting of cblC disease through the newborn screening.

First Chinese case of successful pregnancy with combined methylmalonic aciduria and homocystinuria, cblC type

OBJECTIVE

Combined methylmalonic aciduria (MMA) and homocystinuria, cblC type, is the most common MMA in Mainland China. Its clinical spectrum varies from severe neonatal-onset forms with brain injury and high mortality to milder forms with late onset. Timely diagnosis and adequate treatment greatly improve the prognosis. In the past 15 years, many Chinese patients with this condition have achieved favorable treatment outcomes, and some of them have reached childbearing age. Here, we report the first case of Chinese woman with cblC undergoing a successful pregnancy and delivering a healthy boy.

METHODS

A patient of late-onset cblC, who achieved successful pregnancy and delivery of a healthy boy, was enrolled in our studies. The patient and her disease characteristics were analyzed, including age at onset, age at diagnosis, clinical presentation, clinical classification, family history, laboratory findings and MMACHC gene mutation.

RESULTS

Our patient presented mild neurological symptoms at the age of 15 years. She had the compound heterozygous mutations, c.315C>G and c.482G>A, on the MMACHC gene. After long-term treatment with cobalamin, calcium folinate, l-carnitine and betaine, along with normal diet, she recovered completely. At age 23, she visited us for genetic counseling and fetal evaluation at 15 weeks of gestation. Her general condition and the fetal growth were normal. At 20 weeks of gestation, intramuscular cobalamin was changed to pure hydroxocobalamin (1 mg, every other day) because of markedly elevated urine MMA and plasma total homocysteine. In addition, the dosages of l-carnitine (1 g, p.o., tds), folic acid (5 mg, p.o., tds) and betaine (1 g, p.o., tds) were increased. Protein intake was not restricted.

CONCLUSIONS

This is the first report of a Chinese woman with cblC, undergoing a successful pregnancy and delivering a healthy baby at term. The favorable outcome of the patient and her fetus should owe much to the mild phenotype of her disease.

Hcfc1b, a zebrafish ortholog of HCFC1, regulates craniofacial development by modulating mmachc expression

Mutations in HCFC1 (MIM300019), have been recently associated with cblX (MIM309541), an X-linked, recessive disorder characterized by multiple congenital anomalies including craniofacial abnormalities. HCFC1 is a transcriptional co-regulator that modulates the expression of numerous downstream target genes including MMACHC, but it is not clear how these HCFC1 targets play a role in the clinical manifestations of cblX. To begin to elucidate the mechanism by which HCFC1 modulates disease phenotypes, we have carried out loss of function analyses in the developing zebrafish. Of the two HCFC1 orthologs in zebrafish, hcfc1a and hcfc1b, the loss of hcfc1b specifically results in defects in craniofacial development. Subsequent analysis revealed that hcfc1b regulates cranial neural crest cell differentiation and proliferation within the posterior pharyngeal arches. Further, the hcfc1b-mediated craniofacial abnormalities were rescued by expression of human MMACHC, a downstream target of HCFC1 that is aberrantly expressed in cblX. Furthermore, we tested distinct human HCFC1 mutations for their role in craniofacial development and demonstrated variable effects on MMACHC expression in humans and craniofacial development in zebrafish. Notably, several individuals with mutations in either HCFC1 or MMACHC have been reported to have mild to moderate facial dysmorphia. Thus, our data demonstrates that HCFC1 plays a role in craniofacial development, which is in part mediated through the regulation of MMACHC expression.

Neurologic and neurodevelopmental phenotypes in young children with early-treated combined methylmalonic acidemia and homocystinuria, cobalamin C type

Abnormal neurodevelopment has been widely reported in combined methylmalonic aciduria (MMA) and homocystinuria, cblC type (cblC disease), but neurodevelopmental phenotypes in cblC have not previously been systematically studied. We sought to further characterize developmental neurology in children with molecularly-confirmed cblC. Thirteen children at our center with cblC, born since implementation of expanded newborn screening in New York State, undertook standard-of-care evaluations with a pediatric neurologist and pediatric ophthalmologist. At most recent follow-up (mean age 50 months, range 9-84 months), of twelve children with early-onset cblC, three (25%) had a history of clinical seizures and two (17%) meet criteria for microcephaly. A majority of children had hypotonia and nystagmus. Twelve out of thirteen (92%) underwent neurodevelopmental evaluation (mean age 41 months; range 9-76 months), each child tested with standardized parental interviews and, where possible, age- and disability-appropriate neuropsychological batteries. All patients showed evidence of developmental delay with the exception of one patient with a genotype predictive of attenuated disease and near-normal biochemical parameters. Neurodevelopmental deficits were noted most prominently in motor skills, with relative preservation of socialization and communication skills. Nine children with early-onset cblC underwent magnetic resonance imaging and spectroscopy (MRI/MRS) at mean age of 47 months (range 6-81 months); common abnormalities included callosal thinning, craniocaudally short pons, and increased T2 FLAIR signal in periventricular and periatrial white matter. Our study further characterizes variable neurodevelopmental phenotypes in treated cblC, and provides insights into the etiopathogenesis of disordered neurodevelopment frequently encountered in cblC. Plasma homocysteine and MMA, routinely measured at clinical follow-up, may be poor predictors for neurodevelopmental outcomes. Additional data from large, prospective, multi-center natural history studies are required to more accurately define the role of these metabolites and others, as well as that of other genetic and environmental factors in the etiopathogenesis of the neurologic components of this disorder.