Spectrum of MMACHC mutations in Italian and Portuguese patients with combined methylmalonic aciduria and homocystinuria, cblC type

Improved biochemical and neurodevelopmental profiles with high-dose hydroxocobalamin therapy in cobalamin C defect

Cobalamin C (Cbl-C) defect causes methylmalonic acidemia, homocystinuria, intellectual disability and visual impairment, despite treatment adherence. While international guidelines recommend parenteral hydroxocobalamin (OH-Cbl) as effective treatment, dose adjustments remain unclear. We assessed OH-Cbl therapy impact on biochemical, neurocognitive and visual outcomes in early-onset Cbl-C patients treated with different OH-Cbl doses over 3 years. Group A (n = 5), diagnosed via newborn screening (NBS), received high-dose OH-Cbl (median 0.55 mg/kg/day); Group B1 (n = 3), NBS-diagnosed, received low-dose OH-Cbl (median 0.09 mg/kg/day); Group B2 (n = 12), diagnosed on clinical bases, received low-dose OH-Cbl (median 0.06 mg/kg/day). Biochemical analyses revealed better values of homocysteine, methionine and methylmalonic acid in Group A compared to Group B1 (p < 0.01, p < 0.05 and p < 0.01, respectively) and B2 (p < 0.001, p < 0.01 and p < 0.001, respectively). Neurodevelopmental assessment showed better outcome in Group A compared to low-dose treated Groups B1 and B2, especially in Developmental Quotient, Hearing and Speech and Performance subscales without significant differences between Group B2 and Group B1. Maculopathy was detected in 100%, 66% and 83% of patients in the three groups, respectively. This study showed that "high-dose" OH-Cbl treatment in NBS-diagnosed children with severe early-onset Cbl-C defect led to a significant improvement in the metabolic profile and in neurocognitive outcome, compared to age-matched patients treated with a "low-dose" regimen. Effects on maculopathy seem unaffected by OH-Cbl dosage. Our findings, although observed in a limited number of patients, may contribute to improve the long-term outcome of Cbl-C patients.

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.

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.

Interaction of Glutathione with MMACHC Arginine-Rich Pocket Variants Associated with Cobalamin C Disease: Insights from Molecular Modeling

Methylmalonic aciduria and homocystinuria type C protein (MMACHC) is required by the body to metabolize cobalamin (Cbl). Due to its complex structure and cofactor forms, Cbl passes through an extensive series of absorptive and processing steps before being delivered to mitochondrial methyl malonyl-CoA mutase and cytosolic methionine synthase. Depending on the cofactor attached, MMACHC performs either flavin-dependent reductive decyanation or glutathione (GSH)-dependent dealkylation. The alkyl groups of Cbl have to be removed in the presence of GSH to produce intermediates that can later be converted into active cofactor forms. Pathogenic mutations in the GSH binding site, such as R161Q, R161G, R206P, R206W, and R206Q, have been reported to cause Cbl diseases. The impact of these variations on MMACHC's structure and how it affects GSH and Cbl binding at the molecular level is poorly understood. To better understand the molecular basis of this interaction, mutant structures involving the MMACHC-MeCbl-GSH complex were generated using in silico site-directed point mutations and explored using molecular dynamics (MD) simulations. The results revealed that mutations in the key arginine residues disrupt GSH binding by breaking the interactions and reducing the free energy of binding of GSH. Specifically, variations at position 206 appeared to produce weaker GSH binding. The lowered binding affinity for GSH in the variant structures could impact metabolic pathways involving Cbl and its trafficking.

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.

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.

Acute Lymphoblastic Leukemia in Combined Methylmalonic Acidemia and Homocysteinemia (cblC Type): A Case Report and Literature Review

Background: Methylmalonic acidemia (MMA) can display many clinical manifestations, among which acute lymphoblastic leukemia (ALL) has not been reported, and congenital heart disease (CHD) is also rare.

Case presentation: We report an MMA case with ALL and CHD in a 5.5-year-old girl. With developmental delay and local brain atrophy in MRI, she was diagnosed with cerebral palsy at 9 months old. Rehabilitation was performed since then. This time she was admitted to hospital because of weakness and widespread bleeding spots. ALL-L2 (pre-B-cell) was confirmed by bone marrow morphology and immunophenotyping. Echocardiography showed patent foramen ovale. The girl was treated with VDLD and CAML chemotherapy, during which she developed seizures, edema and renal insufficiency. Decrease of muscle strength was also found in physical examination. Screening for inherited metabolic disorders showed significantly elevated levels of methylmalonate-2, acetylcarnitine (C2), propionylcarnitine (C3), C3/C2 and homocysteine. Gene analysis revealed a compound heterozygous mutaion in MMACHC (NM_015,560): c.80A > G (p.Gln27Arg) and c.609G > A (p.Trp203*). CblC type MMA was diagnosed. Intramuscular injection of cyanocobalamin and intravenous L-carnitine treatment were applied. The edema vanished gradually, and chemotherapy of small dosage of vindesine was given intermittently when condition permitted. 2 months later, muscle strength of both lower limbs were significantly improved to nearly grade 5. The levels of methylmalonic acid and homocysteine were improved.

Conclusion: Metabolic disease screening and gene analysis are very necessary for diseases with complex clinical symptoms. ALL can be a rare manifestation for MMA.

Synopsis: We report a case of methylmalonic acidemia with acute lymphoblastic leukemia and congenital heart disease, which uncovered the importance of genetic testing and metabolic diseases screening in patients with multiple systemic organ involvement.

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.

The Follow-Up of Chinese Patients in cblC Type Methylmalonic Acidemia Identified Through Expanded Newborn Screening

Objective: The cblC type of combined methylmalonic acidemia and homocystinuria, an inherited disorder with variable phenotypes, is included in newborn screening (NBS) programs at multiple newborn screening centers in China. The present study aimed to investigate the long-term clinical benefits of screening individual.

Methods: A national, retrospective multi-center study of infants with confirmed cblC defect identified by NBS between 2004 and 2020 was conducted. We collected a large cohort of 538 patients and investigated their clinical data in detail, including disease onset, biochemical metabolites, and gene variation, and explored different factors on the prognosis.

Results: The long-term outcomes of all patients were evaluated, representing 44.6% for poor outcomes. In our comparison of patients with already occurring clinical signs before treatment to asymptomatic ones, the incidence of intellectual impairment, movement disorders, ocular complications, hydrocephalus, and death were significantly different (p < 0.01). The presence of disease onset [Odd ratio (OR) 12.39, 95% CI 5.15–29.81; p = 0.000], variants of c.609G>A (OR 2.55, 95% CI 1.49–4.35; p = 0.001), and c.567dupT (OR 2.28, 95% CI 1.03–5.05; p = 0.042) were independently associated with poor outcomes, especially for neurodevelopmental deterioration.

Conclusion: NBS, avoiding major disease-related events and allowing an earlier treatment initiation, appeared to have protective effects on the prognosis of infants with cblC defect.

Prominent renal complications associated with MMACHC pathogenic variant c.80A > G in Chinese children with cobalamin C deficiency

OBJECTIVE

CblC deficiency, the most common cobalamin metabolic abnormality, is caused by pathogenic variants in the MMACHC gene. The renal complications of this disease have been described only in a small number of cases. This study aimed to better delineate renal phenotype and genetic characteristics in Chinese children with cblC defect.

METHODS

Children with cblC deficiency who manifested as kidney damage were enrolled. Clinical, renal pathological, and genetic data were reviewed in detail.

RESULTS

Seven cases were enrolled. Ages at disease onset ranged from 9 months to 5 years. All patients presented with hematuria and proteinuria, and 2/7 cases presented with nephrotic syndrome. Renal dysfunction was observed in 4/7 cases. Renal biopsy was performed in 5/7 cases, and all of them had renal thrombotic microangiopathy. Macrocytic anemia was detected in all seven patients. Six out of seven cases had hypertension, and 2/7 cases presented with pulmonary hypertension. Two of them had a mild intellectual disability, and one suffered from epilepsy. Increased urine methylmalonic acid and plasma homocysteine were detected in seven cases, while two patients had normal levels of urine methylmalonic acid at the initial evaluation. After diagnosis, all seven cases were treated with hydroxocobalamin IM. Six cases were followed-up for 3-8 years. After treatments, anemia was the first to be recovered, followed by proteinuria. Renal function recovered after 1 year in two cases, whereas patient 2 progressed to stage 2 chronic kidney disease 13 years after onset. While a case presented with end-stage kidney disease because of late diagnosis, one case died 3 months after disease onset due to giving up treatment. Three MMACHC pathogenic variants c.80A > G (8/14), c.609G > A (4/14), and c.658_660delAAG (2/14) were detected in all seven children.

CONCLUSION

MMACHC variant c.80A > G may be associated with prominent renal complications in Chinese cblC patients. Macrocytic anemia and hyperhomocysteinemia are useful clues for patients with hematuria and proteinuria caused by cblC defect. The most frequent renal pathological manifestation is thrombotic microangiopathy. Early diagnosis and treatment resulted in improving renal and hematological signs.

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.

Ocular manifestations in patients with inborn errors of intracellular cobalamin metabolism: a systematic review

Inherited disorders of cobalamin (cbl) metabolism (cblA-J) result in accumulation of methylmalonic acid (MMA) and/or homocystinuria (HCU). Clinical presentation includes ophthalmological manifestations related to retina, optic nerve and posterior visual alterations, mainly reported in cblC and sporadically in other cbl inborn errors.We searched MEDLINE EMBASE and Cochrane Library, and analyzed articles reporting ocular manifestations in cbl inborn errors. Out of 166 studies a total of 52 studies reporting 163 cbl and 24 mut cases were included. Ocular manifestations were found in all cbl defects except for cblB and cblD-MMA; cblC was the most frequent disorder affecting 137 (84.0%) patients. The c.271dupA was the most common pathogenic variant, accounting for 70/105 (66.7%) cases. One hundred and thirty-seven out of 154 (88.9%) patients presented with early-onset disease (0-12 months). Nystagmus and strabismus were observed in all groups with the exception of MMA patients while maculopathy and peripheral retinal degeneration were almost exclusively found in MMA-HCU patients. Optic nerve damage ranging from mild temporal disc pallor to complete atrophy was prevalent in MMA-HCU.and MMA groups. Nystagmus was frequent in early-onset patients. Retinal and macular degeneration worsened despite early treatment and stabilized systemic function in these patients. The functional prognosis remains poor with final visual acuity < 20/200 in 55.6% (25/45) of cases. In conclusion, the spectrum of eye disease in Cbl patients depends on metabolic severity and age of onset. The development of visual manifestations over time despite early metabolic treatment point out the need for specific innovative therapies.

Implementation of second-tier tests in newborn screening for the detection of vitamin B12 related acquired and genetic disorders: results on 258,637 newborns

BACKGROUND

Alteration of vitamin B₁₂ metabolism can be genetic or acquired, and can result in anemia, failure to thrive, developmental regression and even irreversible neurologic damage. Therefore, early diagnosis and intervention is critical. Most of the neonatal cases with acquired vitamin B₁₂ deficiency have been detected by clinical symptoms and only few of them trough NBS programs. We aim to assess the usefulness of the second-tier test: methylmalonic acid (MMA), methylcitric acid (MCA) and homocysteine (Hcys) in our newborn screening program and explore the implications on the detection of cobalamin (vitamin B₁₂) related disorders, both genetic and acquired conditions.

METHODS

A screening strategy using the usual primary markers followed by the analysis of MMA, MCA and Hcys as second tier-test in the first dried blood spot (DBS) was developed and evaluated.

RESULTS

During the period 2015-2018 a total of 258,637 newborns were screened resulting in 130 newborns with acquired vitamin B₁₂ deficiency (incidence 1:1989), 19 with genetic disorders (incidence 1:13,613) and 13 were false positive. No false negatives were notified. Concerning the second-tier test, the percentage of cases with MMA above the cut-off levels, both for genetic and acquired conditions was very similar (58% and 60%, respectively). Interestingly, the percentage of cases with increased levels of Hcys was higher in acquired conditions than in genetic disorders (87% and 47%, respectively). In contrast, MCA was high only in 5% of the acquired conditions versus in 53% of the genetic disorders, and it was always very high in all patients with propionic acidemia.

CONCLUSIONS

When screening for methylmalonic acidemia and homocystinuria, differential diagnosis with acquired vitamin B₁₂ deficiency should be done. The results of our strategy support the inclusion of this acquired condition in the NBS programs, as it is easily detectable and allows the adoption of corrective measures to avoid the consequences of its deficiency.

Combined Genome, Transcriptome and Metabolome Analysis in the Diagnosis of Childhood Cerebellar Ataxia

Ataxia in children is a common clinical sign of numerous neurological disorders consisting of impaired coordination of voluntary muscle movement. Its most common form, cerebellar ataxia, describes a heterogeneous array of neurologic conditions with uncountable causes broadly divided as acquired or genetic. Numerous genetic disorders are associated with chronic progressive ataxia, which complicates clinical management, particularly on the diagnostic stage. Advances in omics technologies enable improvements in clinical practice and research, so we proposed a multi-omics approach to aid in the genetic diagnosis and molecular elucidation of an undiagnosed infantile condition of chronic progressive cerebellar ataxia. Using whole-exome sequencing, RNA-seq, and untargeted metabolomics, we identified three clinically relevant mutations (rs141471029, rs191582628 and rs398124292) and an altered metabolic profile in our patient. Two POLR1C diagnostic variants already classified as pathogenic were found, and a diagnosis of hypomyelinating leukodystrophy was achieved. A mutation on the MMACHC gene, known to be associated with methylmalonic aciduria and homocystinuria cblC type, was also found. Additionally, preliminary metabolome analysis revealed alterations in our patient’s amino acid, fatty acid and carbohydrate metabolism. Our findings provided a definitive genetic diagnosis reinforcing the association between POLR1C mutations and hypomyelinating leukodystrophy and highlighted the relevance of multi-omics approaches to the disease.

Value of amniotic fluid homocysteine assay in prenatal diagnosis of combined methylmalonic acidemia and homocystinuria, cobalamin C type

BACKGROUND

Combined methylmalonic acidemia and homocystinuria, cobalamin C type (cblC defect) is the most common inborn error of cobalamin metabolism, and different approaches have been applied to its prenatal diagnosis. To evaluate the reliability of biochemical method for the prenatal diagnosis of cblC defect, we conducted a retrospective study of our 10-year experience at a single center.

METHODS

248 pregnancies whose probands were diagnosed as cblC defect were referred to our center for prenatal diagnosis from January 2010 to December 2019. Prenatal data of Hcy levels determined by enzymatic cycling assay, acylcarnitine analysis using liquid chromatography tandem mass spectrometry, organic acid analysis using gas chromatography mass spectrometry, and genetic analysis by direct sequencing of 248 at-risk fetuses were retrospectively reviewed.

RESULTS

For 2.0 and 16.0 μmol/L levels of Hcy AF samples, the relative errors were - 2.5% and 2.8%, respectively. The respective measurement uncertainties were 13.07% and 14.20%. For the 248 at-risk fetuses, 63 fetuses were affected and 185 fetuses were unaffected. Hcy level of 13.20 (6.62-43.30) μmol/L in 63 affected fetuses was significantly higher than that in 185 unaffected fetuses of 2.70 (0.00-5.80) μmol/L, and there was no overlap between the affected and unaffected groups. The diagnostic sensitivity and specificity of Hcy were 100% and 92.05%, respectively. The positive and negative predictive values of the combination of Hcy, propionylcarnitine (C3), ratio of C3 to acetylcarnitine (C2; C3/C2), methylmalonic acid (MMA), and methylcitric acid (MCA) were both 100%. Sixteen fetuses displayed inconclusive genetic results of MMACHC variants, in which seven fetuses were determined to be affected with elevated levels of Hcy, C3, C3/C2 and MMA, and their levels were 18.50 (6.70-43.30) μmol/L, 8.53(5.02-11.91) μmol/L, 0.77 (0.52-0.97), 8.96 (6.55-40.32) mmol/mol Cr, respectively. The remaining nine fetuses were considered unaffected based on a normal amniotic fluid metabolite profile.

CONCLUSIONS

Hcy appears to be another characteristic biomarker for the prenatal diagnosis of cblC defect. The combination of Hcy assay with acylcarnitine and organic acid analysis is a fast, sensitive, and reliable prenatal diagnostic biochemical approach. This approach could overcome the challenge of the lack of genetic analysis for families with at-risk cblC defect fetuses.

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.

Development of infantile tremor syndrome after initiation of hydroxycobalamin treatment in an infant with a late diagnosis of cobalamin C disorder

Combined methylmalonic aciduria and homocystinuria (cobalamin C deficiency, cblC) is a well-described disorder of vitamin B12 metabolism caused by mutations in the MMACHC gene with multisystemic manifestations. While there is no cure, combined treatment with intramuscular hydroxycobalamin and oral betaine may reduce the severity of symptoms and improve clinical outcome. We report a female patient diagnosed with late-onset cobalamin C deficiency at the age of 8 months who presented with developmental regression and severe dermatitis. She developed a movement disorder after initiation of hydroxycobalamin treatment. Similar movement disorders have been described in patients with nutritional vitamin B12 deficiencies following cobalamin supplementation but have not previously been reported in patients with cobalamin C disorder. The movement disorder in our patient gradually resolved with clonazepam treatment, despite no seizure activity detected on EEG. She was eventually weaned off the clonazepam and the abnormal movements have not recurred. The patient remains developmentally delayed but is showing no other symptoms related to cobalamin C deficiency. The patient has a younger affected sibling who was treated from birth and who is physically and developmentally entirely normal; she did not have abnormal movements after treatment with hydroxycobalamin was initiated. There is no clear consensus on the cause of movement disorders that develop following initiation of intramuscular vitamin B12 treatment.

Vitamin B12 deficiency and metabolism-mediated thrombotic microangiopathy (MM-TMA)

Thrombotic microangiopathies (TMA) are characterized by microangiopathic hemolytic anemia, thrombocytopenia and organ damage resulting from mechanical factors, accumulation of the ultra-large von Willebrand factor multimers or complement-mediated abnormalities. Severe acquired vitamin B12 (Cobalamin - Cbl) deficiency or congenital defective Cbl metabolism could lead to a picture that mimics TMA. The later has been termed metabolism-mediated TMA (MM- TMA). This confusing picture is mediated partly by the large red cell fragmentation coupled with reduced platelet production in the absence of vitamin B12 and partly by the accumulated byproducts and metabolites that induce endothelial injury and hence organ damage. Expensive and complicated treatment for TMA is often initiated on an empiric basis, pending the results of confirmatory tests. In contrast, vitamin B12 Pseudo-TMA and MM-TMA could be treated with proper vitamin B12 supplementation. It is therefore important to identify these disorders promptly. The recent availability of a validated scoring system such as the PLASMIC score uses simple clinical and laboratory parameters. As it incorporates the mean corpuscular volume in its laboratory parameters, this helps in the identification of pseudo and MM-TMA. Perhaps some minor modification of this scoring system by changing the parameters of hemolysis to include reticulocytosis and rather than and/or other hemolytic parameters could even help refine this identification.

Parenteral hydroxocobalamin dose intensification in five patients with different types of early onset intracellular cobalamin defects: Clinical and biochemical responses

Intracellular cobalamin metabolism (ICM) defects can be present as autosomal recessive or X-linked disorders. Parenteral hydroxocobalamin (P-OHCbl) is the mainstay of therapy, but the optimal dose has not been determined. Despite early treatment, long-term complications may develop. We have analyzed the biochemical and clinical responses in five patients with early onset of different types of ICM defects (cblC: patients 1-3; cblA: patient 4; cblX: patient 5) following daily P-OHCbl dose intensification (DI). In patient 4, P-OHCbl was started at age 10 years and in patient 5 at age 5 years. OHCbl was formulated at either, 5, 25, or 50 mg/mL. P-OHCbl was intravenously or subcutaneously (SQ) delivered, subsequently by placement of a SQ injection port except in patient 4. In all patients, homocysteine and methylmalonic acid levels, demonstrated an excellent response to various P-OHCbl doses. After age 36 months, patients 1-3 had a close to normal neurological examination with lower range developmental quotient. In patient 3, moderate visual impairment was present. Patient 4, at age 10 years, had normal renal, visual and cognitive function. In cblX patient 5, epilepsy was better controlled. In conclusion, P-OHCbl-DI caused an excellent control of metabolites in all patients. In the three cblC patients, comparison with patients, usually harboring identical genotype and similar metabolic profile, was suggestive of a positive effect, in favor of clinical efficacy. With P-OHCbl-DI, CblA patient has been placed into a lower risk to develop renal and optic impairment. In cblX patient, lower P-OHCbl doses were administrated to improve tolerability.

Hereditary defect of cobalamin metabolism with adolescence onset resembling multiple sclerosis: 41-year follow up in two cases

The cblC defect is the most common inborn error of cobalamin (Cbl) metabolism. Clinical severity and presentation of the cblC defect ranges from death to mild disability. Only 71 cases of late-onset cblC defect have been described in the literature. We provide the 41-year follow up of two siblings with a late-onset cblC defect, first described after initial diagnosis in 1996. While one of the siblings showed initial symptoms resembling multiple sclerosis with a good response to corticosteroids, the other sister showed only subclinical signs of the disease. The course of the first case was characterized by a severe deterioration and intensive-care therapy after respiratory failure. After diagnoses and Cbl treatment, the patient survived and showed a pronounced improvement of the symptoms. Both sisters have an active life and gave birth to healthy children. The reason for the initial improvement after corticosteroids could not be explained by the classical metabolic pathways of Cbl. Recent studies have suggested that Cbl plays an important role as a regulator of the balance between neurotrophic and neurotoxic factors in the central and peripheral nervous system (CNS and PNS). This first long-term follow up revealed that ultra-high-dose intramuscular Hydroxocobalamin (OH-Cbl) treatment can effectively protect patients from disease progression. It underlines the importance of diagnostic vigilance and laboratory work up even in cases without typical hematologic signs of Cbl deficiency. Cbl-related diseases are often a chameleon and must always be considered in the differential of demyelinating diseases of the PNS and CNS. The case supports the theory that it is not only the classical biochemical pathways that play a key role in Cbl deficiency, especially with regard to neurological symptoms.

The clinical presentation of cobalamin-related disorders: From acquired deficiencies to inborn errors of absorption and intracellular pathways

This review gives an overview of clinical characteristics, treatment and outcome of nutritional and acquired cobalamin (Cbl; synonym: vitamin B12) deficiencies, inborn errors of Cbl absorption and intracellular trafficking, as well as methylenetetrahydrofolate dehydrogenase (MTHFD1) and methylene tetrahydrofolate reductase (MTHFR) deficiencies, which impair Cbl-dependent remethylation. Acquired and inborn Cbl-related disorders and MTHFR deficiency cause multisystem, often severe disease. Failure to thrive, neurocognitive or psychiatric symptoms, eye disease, bone marrow alterations, microangiopathy and thromboembolic events are characteristic. The recently identified MTHFD1 defect additionally presents with severe immune deficiency. Deficient Cbl-dependent enzymes cause reduced methylation capacity and metabolite toxicity. Further net-effects of perturbed Cbl function or reduced Cbl supply causing oxidative stress, altered cytokine regulation or immune functions are discussed.

Distinct clinical, neuroimaging and genetic profiles of late-onset cobalamin C defects (cb1C): a report of 16 Chinese cases

Objective

The importance of late-onset cobalamin C (cblC) disorder is underestimated in adults. Improved awareness on its clinical and neuroimaging features helps timely diagnosis and appropriate treatment.

Methods

Totally 16 late-onset cblC cases were diagnosed based on clinical, biochemical findings and MMAHC gene mutation analysis. Clinical presentations, neuroimaging features and mutational spectrum were reviewed.

Results

The case series included 10 males and 6 females, with average age of 22 (range 13–40) years. All the 16 patients displayed bilateral pyramidal tract signs, and most of the cases (13) had cognitive impairment. Other symptoms included psychiatric symptoms (6), epilepsy (6), peripheral nerve damage (5), ocular symptoms (4) and lower-limb thrombosis (1). The neuroimaging findings were dominated by cerebral atrophy (11/16), followed by white matter lesions (4), cerebellar lesions/atrophy (2) and spinal cord lesions (1). There were also 2 patients with normal imaging. All the MMACHC mutations were compound heterozygous, of which the most and second frequent was c.482G > A (p.R161Q; 15/16 case; allele frequency: 46.88%) and c.609G > A(p.W203X; 6/16 case; allele frequency: 18.75%). In addition, patients carrying frameshift mutations (deletion/duplication) presented more frequently with psychiatric symptoms (57.1%) and optic nerve damages (42.9%) than those carrying point mutations (22.2 and 11.1%, respectively). In contrast, peripheral nerve (44.4%) and white matter lesions (33.3%) were more frequently identified in point mutation- carriers. However, the differences did not achieve statistical significance (all p > 0.05).

Conclusion

Compared to the early-onset form, late-onset cblC displayed some clinical, neuroimaging and mutational profiles, which warrants particular attention in adult neurologic practice. These findings not only broaden our insights into the genotypes and phenotypes of the disease, but highlight the importance of early diagnosis and initiation of appropriate treatments.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1058-9) contains supplementary material, which is available to authorized users.

Phenotype, treatment practice and outcome in the cobalamin-dependent remethylation disorders and MTHFR deficiency: Data from the E-HOD registry

AIM

To explore the clinical presentation, course, treatment and impact of early treatment in patients with remethylation disorders from the European Network and Registry for Homocystinurias and Methylation Defects (E-HOD) international web-based registry.

RESULTS

This review comprises 238 patients (cobalamin C defect n = 161; methylenetetrahydrofolate reductase deficiency n = 50; cobalamin G defect n = 11; cobalamin E defect n = 10; cobalamin D defect n = 5; and cobalamin J defect n = 1) from 47 centres for whom the E-HOD registry includes, as a minimum, data on medical history and enrolment visit. The duration of observation was 127 patient years. In 181 clinically diagnosed patients, the median age at presentation was 30 days (range 1 day to 42 years) and the median age at diagnosis was 3.7 months (range 3 days to 56 years). Seventy-five percent of pre-clinically diagnosed patients with cobalamin C disease became symptomatic within the first 15 days of life. Total homocysteine (tHcy), amino acids and urinary methylmalonic acid (MMA) were the most frequently assessed disease markers; confirmatory diagnostics were mainly molecular genetic studies. Remethylation disorders are multisystem diseases dominated by neurological and eye disease and failure to thrive. In this cohort, mortality, thromboembolic, psychiatric and renal disease were rarer than reported elsewhere. Early treatment correlates with lower overall morbidity but is less effective in preventing eye disease and cognitive impairment. The wide variation in treatment hampers the evaluation of particular therapeutic modalities.

CONCLUSION

Treatment improves the clinical course of remethylation disorders and reduces morbidity, especially if started early, but neurocognitive and eye symptoms are less responsive. Current treatment is highly variable. This study has the inevitable limitations of a retrospective, registry-based design.

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.

Clinical feature and outcome of late-onset cobalamin C disease patients with neuropsychiatric presentations: a Chinese case series

OBJECTIVE

The Cobalamin C (cblC) disease is an inborn error of cobalamin metabolism. Late-onset cblC disease was diagnosed in patients having overt symptoms after 4 years of age. The late-onset cblC disease patients were rare and easily misdiagnosed. This study analyzed the clinical presentations, gene mutations, and treatments of Chinese patients with late-onset cblC disease.

METHODS

The clinical data of 26 Han Chinese patients diagnosed with late-onset cblC disease were retrospectively analyzed. All patients underwent serum homocysteine level exam, urine concentrations of organic acids measurement, neuroimaging scans, gene analysis, and treatments evaluations.

RESULTS

The mean age at disease onset and diagnosis was 17.8±7.0 years. The most frequent neuropsychiatric disturbances were lower limb weakness (50%), psychiatric disturbances (46.2%), and gait instability (42.3%). The mean methylmalonic acid level in urine was 107.4±56.6 μmol/L, and mean serum total homocysteine was 105.4±41.0 μmol/L. The most common abnormal radioimaging changes were observed in the spinal cord (88%) and brain (32%). Scoliosis was detected in 85.7% of patients. The methylmalonic aciduria and homocystinuria type C protein gene analysis showed that c.482G>A (57.7%) and c.609G>A (34.6%) mutations were the most frequent genotypes. After treatments with hydroxycobalamin, betaine, folic acid, L-carnitine, and compound vitamin B, the clinical features and biochemical parameters of patients with late-onset cblC disease were found to be alleviated.

CONCLUSION

In our late-onset cblC disease cases, lower limb weakness, psychiatric disturbances, and gait instability were the most frequent manifestations. Patients responded well to the drug treatments with hydrocobalamin and betaine. When juvenile or adult patients with hyperhomocysteinemia present with neurological symptoms, cblC disease needs to be considered.

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.

Atypical adult-onset methylmalonic acidemia and homocystinuria presenting as hemolytic uremic syndrome

Thrombotic microangiopathy (TMA) syndromes can be secondary to a multitude of different diseases. Most can be identified with a systematic approach and, when excluded, TMA is generally attributed to a dysregulation in the activity of the complement alternative pathways-atypical hemolytic uremic syndrome (aHUS). We present a challenging case of a 19-year-old woman who presented with thrombotic microangiopathy, which was found to be caused by methylmalonic acidemia and homocystinuria, a rare vitamin B12 metabolism deficiency. To our knowledge, this is the first time that an adult-onset methylmalonic acidemia and homocystinuria presents as TMA preceding CNS involvement.

Renal thrombotic microangiopathy and pulmonary arterial hypertension in a patient with late-onset cobalamin C deficiency

Cobalamin C (cblC) deficiency is the most commonly inherited inborn error of vitamin B12 metabolism. It is characterized by multisystem involvement with severe neurological, hematological, renal and cardiopulmonary manifestations. Disease is most commonly diagnosed early in the first decade of life. We report a case of a 20-year-old woman who developed severe pulmonary arterial hypertension while under nephrologic follow-up for chronic kidney disease. She had initially presented at 14 years of age with visual disturbance and acute renal failure and been diagnosed with thrombotic thrombocytopenic purpura on the basis of kidney biopsy findings of thrombotic microangiopathy and compatible ADAMTS13 (a disentegrin and metalloproteinase with a thrombospondin type 1 motif member 13). When cblC deficiency was eventually diagnosed, remarkable improvement in cardiopulmonary function was evident upon initiation of treatment. This case highlights the importance of a timely diagnosis and initiation of treatment for cblC deficiency. Clinical diagnosis may be challenged by asynchronous organ symptom presentation and by misleading laboratory tests, in this case: an initial low ADAMTS13. A simple test of plasma homocysteine level should be encouraged in cases of thrombotic microangiopathy and/or pulmonary artery hypertension.

Milder clinical and biochemical phenotypes associated with the c.482G>A (p.Arg161Gln) pathogenic variant in cobalamin C disease: Implications for management and screening

INTRODUCTION

Cobalamin C disease is a multisystemic disease with variable manifestations and age of onset. Genotype-phenotype correlations are well-recognized in this disorder. Here, we present a large cohort of individuals with cobalamin C disease, several of whom are heterozygous for the c.482G>A pathogenic variant (p.Arg161Gln). We compared clinical characteristics of individuals with this pathogenic variant to those who do not have this variant. To our knowledge, this study represents the largest single cohort of individuals with the c.482G>A (p.Arg161Gln) pathogenic variant.

METHODS

A retrospective chart review of 27 individuals from 21 families with cobalamin C disease who are followed at our facility was conducted.

RESULTS

13 individuals (48%) are compound heterozygous with the c.482G>A (p.Arg161Gln) on one allele and a second pathogenic variant on the other allele. Individuals with the c.482G>A (p.Arg161Gln) pathogenic variant had later onset of symptoms and easier metabolic control. Moreover, they had milder biochemical abnormalities at presentation which likely contributed to the observation that 4 individuals (31%) in this group were missed by newborn screening.

CONCLUSION

The c.482G>A (p.Arg161Gln) pathogenic variant is associated with milder disease. These individuals may not receive a timely diagnosis as they may not be identified on newborn screening or because of unrecognized, late onset symptoms. Despite the milder presentation, significant complications can occur, especially if treatment is delayed.

Late Onset Cobalamin Disorder and Hemolytic Uremic Syndrome: A Rare Cause of Nephrotic Syndrome

Hemolytic uremic syndrome (HUS) is an unrare and severe thrombotic microangiopathy (TMA) caused by several pathogenetic mechanisms among which Shiga toxin-producing Escherichia coli infections and complement dysregulation are the most common. However, very rarely and particularly in neonates and infants, disorders of cobalamin metabolism (CblC) can present with or be complicated by TMA. Herein we describe a case of atypical HUS (aHUS) related to CblC disease which first presented in a previously healthy boy at age of 13.6 years. The clinical picture was initially dominated by nephrotic range proteinuria and severe hypertension followed by renal failure. The specific treatment with high dose of hydroxycobalamin rapidly obtained the remission of TMA and the complete recovery of renal function. We conclude that plasma homocysteine and methionine determinations together with urine organic acid analysis should be included in the diagnostic work-up of any patient with TMA and/or nephrotic syndrome regardless of age.

Guidelines for diagnosis and management of the cobalamin-related remethylation disorders cblC, cblD, cblE, cblF, cblG, cblJ and MTHFR deficiency

BACKGROUND

Remethylation defects are rare inherited disorders in which impaired remethylation of homocysteine to methionine leads to accumulation of homocysteine and perturbation of numerous methylation reactions.

OBJECTIVE

To summarise clinical and biochemical characteristics of these severe disorders and to provide guidelines on diagnosis and management.

DATA SOURCES

Review, evaluation and discussion of the medical literature (Medline, Cochrane databases) by a panel of experts on these rare diseases following the GRADE approach.

KEY RECOMMENDATIONS

We strongly recommend measuring plasma total homocysteine in any patient presenting with the combination of neurological and/or visual and/or haematological symptoms, subacute spinal cord degeneration, atypical haemolytic uraemic syndrome or unexplained vascular thrombosis. We strongly recommend to initiate treatment with parenteral hydroxocobalamin without delay in any suspected remethylation disorder; it significantly improves survival and incidence of severe complications. We strongly recommend betaine treatment in individuals with MTHFR deficiency; it improves the outcome and prevents disease when given early.

[Gene mutation analysis and prenatal diagnosis of four pedigrees with methymalonic aciduria]

OBJECTIVE

To study gene mutations in four pedigrees with methymalonic aciduria, as well as the feasibility of prenatal diagnosis of methymalonic aciduria.

METHODS

High-throughput sequencing was performed for related genes in the peripheral blood of children or parents who were diagnosed with methymalonic aciduria to identify the loci with mutations. Then amplification primers were designed for each locus, and PCR and direct sequencing were performed to validate the sequencing in the first generation in the four pedigrees. Whether the mutations were pathogenic were determined with reference to literature review and medical history. In the pedigrees 1, 3, and 4, ultrasound-guided chorionic villi biopsy was performed at weeks 11-13 of pregnancy to perform early prenatal diagnosis.

RESULTS

In pedigree 1, c.656A>T and c.729-730insTT heterozygous mutations in the MUT gene were detected in the proband's father and mother, respectively. Early prenatal diagnosis showed c.656A>T and c.729-730insTT double heterozygous mutations in the fetus. The couple decided to terminate pregnancy. In pedigree 2, c.1106G>A and c.755-756insA double heterozygous mutations in the MUT gene were detected in the proband. c.1106G>A came from the father and c.755-756insA came from the mother. In pedigree 3, c.217C>T and c.609G>A double heterozygous mutations in the MMACHC gene were detected in the proband. c.217C>T came from the father and c.609G>A came from the mother. Prenatal diagnosis showed c.609G>A heterozygous mutation in the fetus. The baby was successfully delivered, and the result of umbilical cord blood testing was consistent with the prenatal diagnosis. In pedigree 4, c.609G>A and c.567dupT double heterozygous mutations in the MMACHC gene were detected in the proband. c.609G>A came from the father and c.567dupT came from the mother. Prenatal diagnosis showed c.567dupT heterozygous mutation in the fetus. The baby was successfully delivered, and the result of umbilical cord blood testing was consistent with the prenatal diagnosis.

CONCLUSIONS

Identification of gene mutations helps with prenatal diagnosis in pedigrees with methymalonic aciduria.

Molecular picture of cobalamin C/D defects before and after newborn screening era

Objective

Birth prevalence of Cobalamin (Cbl) C or D defects in Portugal is an estimated 1:85,000, one of the highest worldwide. We compared the genotype/phenotype of patients identified with CblC or CblD before and after the implementation of expanded newborn screening.

Methods

Twenty-five Portuguese CblC/D patients, 14 symptomatic and 11 identified through screening, were diagnosed using gas chromatography or tandem mass spectrometry. Molecular characterization was performed through the study of MMACHC and MMADHC genes.

Results

The most common MMACHC mutation, c.271dupA, was present in 100% of MMACHC alleles of all CblC screened patients, in contrast with the 61% identified before expanded newborn screening. All studied cases (except one, who presented a CblD deficiency) presented a CblC defect. More CblC late-onset patients were diagnosed before the introduction of newborn screening than in the post newborn screening era, probably because some early onset patients died without a definitive diagnosis.

Conclusion

The molecular data found in this cohort contribute to the improvement of screening and diagnosis of Cbl defects and would enable a confirmatory diagnosis of these patients, reducing the need for complex, costly, laborious, and time-consuming biochemical/enzymatic tests.

Whole Exome Sequencing Identifies an Adult-Onset Case of Methylmalonic Aciduria and Homocystinuria Type C (cblC) with Non-Syndromic Bull's Eye Maculopathy

Background: Methylmalonic aciduria and homocystinuria type C (cblC), a disorder of vitamin B12 (cobalamin) metabolism caused by mutations in the MMACHC gene, presents with many systemic symptoms, including neurological, cognitive, psychiatric, and thromboembolic events. Retinal phenotypes, including maculopathy, pigmentary retinopathy, and optic atrophy are common in early onset form of the disease but are rare in adult onset forms.

Materials and Methods: An adult Hispanic female presented with decreased central vision, bilateral pericentral ring scotomas and bull’s eye-appearing macular lesions at 28 years of age. Her medical history was otherwise unremarkable except for iron deficiency anemia and both urinary tract and kidney infections. Screening of the ABCA4 gene, mutations in which frequently cause bull’s eye maculopathy, was negative. Subsequently, analysis with whole exome sequencing was performed.

Results: Whole exome sequencing discovered compound heterozygous mutations in MMACHC, c.G482A:p.Arg161Gln and c.270_271insA:p.Arg91Lysfs*14, which segregated with the disease in the family. The genetic diagnosis was confirmed by biochemical laboratory testing, showing highly elevated urine methylmalonic acid/creatinine and homocysteine levels, and suggesting disease management with hydroxycobalamin injections and carnitine supplementation.

Conclusions: In summary, a unique case of an adult patient with bull’s eye macular lesions and no clinically relevant systemic symptoms was diagnosed with cblC by genetic screening and follow-up biochemical laboratory tests.

Cobalamin C Deficiency Shows a Rapidly Progressing Maculopathy With Severe Photoreceptor and Ganglion Cell Loss

PURPOSE

To describe in detail the retinal structure and function of a group of patients with cobalamin C (cblC) disease.

METHODS

Patients (n = 11, age 4 months to 15 years) with cblC disease (9/11, early onset) diagnosed by newborn screening underwent complete ophthalmic examinations, fundus photography, near-infrared reflectance imaging, and spectral-domain optical coherence tomography (SD-OCT). Electroretinograms (ERGs) were performed in a subset of patients.

RESULTS

Patients carried homozygous or compound heterozygote mutations in the methylmalonic aciduria and homocystinuria type C (MMACHC) gene. Late-onset patients had a normal exam. All early-onset patients showed a maculopathy; older subjects had a retina-wide degeneration (n = 4; >7 years of age). In general, retinal changes were first observed before 1 year of age and progressed within months to a well-established maculopathy. Pseudocolobomas were documented in three patients. Measurable visual acuities ranged from 20/200 to 20/540. Nystagmus was present in 8/11 patients; 5/6 patients had normal ERGs; 1/6 had reduced rod-mediated responses. Spectral-domain OCT showed macular thinning, with severe ganglion cell layer (GCL) and outer nuclear layer (ONL) loss. Inner retinal thickening was observed in areas of total GCL/ONL loss. A normal lamination pattern in the peripapillary nasal retina was often seen despite severe central and/or retina-wide disease.

CONCLUSIONS

Patients with early-onset cblC and MMACHC mutations showed an early-onset, unusually fast-progressing maculopathy with severe central ONL and GCL loss. An abnormally thickened inner retina supports a remodeling response to both photoreceptor and ganglion cell degeneration and/or an interference with normal development in early-onset cblC.

Successful intrauterine treatment of a patient with cobalamin C defect

Cobalamin C (cblC) defect is an inherited autosomal recessive disorder that affects cobalamin metabolism. Patients are treated with hydroxycobalamin to ameliorate the clinical features of early-onset disease and prevent clinical symptoms in late-onset disease. Here we describe a patient in whom prenatal maternal treatment with 30 mg/week hydroxycobalamin and 5 mg/day folic acid from week 15 of pregnancy prevented disease manifestation in a girl who is now 11 years old with normal IQ and only mild ophthalmic findings. The affected older sister received postnatal treatment only and is severely intellectually disabled with severe ophthalmic symptoms. This case highlights the potential of early, high-dose intrauterine treatment in a fetus affected by the cblC defect.

Prenatal diagnosis using genetic sequencing and identification of a novel mutation in MMACHC

BACKGROUND

Combined methylmalonic aciduria and homocystinuria, cobalamin(cbl)C deficiency, is a rare disorder of intracellular vitamin B12(cbl) metabolism caused by mutations in the MMACHC gene. Both genetic and biochemical approach have been established to diagnose children and fetuses with cblC deficiency, while in China there is no report of prenatal genetic diagnosis of cblC deficiency. The aim of the present study was to characterize the mutational spectrum of cblC deficiency and investigate the feasibility of genetic-sequencing-based prenatal diagnosis for cblC deficiency.

METHODS

10 pedigrees were recruited in this study with the probands clinically and biochemically confirmed combined methymalonic aciduria and homocystinuria. Peripheral blood samples were collected for MMACHC genetic test from the probands and their parents (4 probands had already dead) and 50 control subjects. The entire coding region and adjacent splice sites of MMACHC were sequenced. After the genotypes of the pedigrees were identified, chorionic villi sampling were performed for 3 high-risk pregnant women for prenatal genetic diagnosis.

RESULTS

A total of 7 mutations were identified: c.217C > T (R73X), c.394C > T (R132X), c.463G > C (G155R), c.609G > A (W203X), c.616C > T (R206W), c.658-660delAAG (220delK), and c.567dupT (I190YfsX13), as well as 2 polymophsims: c.321G > A(V107V), c.-302G > T. And G155R is a novel mutation that haven't been reported in the literatures. All the 6 probands identified with compound heterozygous mutations or homozygous mutations of MMACHC gene, and all the parents of the probands were found to have one MMACHC mutation at a heterozygous level. Prenatal diagnosis of fetuses from 3 families with a child affected cblC deficiency showed that one fetus had the same compound heterozygous mutations as the proband, one did not have MMACHC mutation, and the third fetus had a mutation at a heterozygous level of MMACHC gene. Results from the follow-ups were consistent with the prenatal diagnosis.

CONCLUSION

A novel mutation p.G155R of the MMACHC gene is identified. Genetic diagonsis is an accurate and convenient method for prenatal diagnosis and early intervention of combined methylmalonic aciduria and homocystinuria.

A treatable metabolic cause of encephalopathy: cobalamin C deficiency in an 8-year-old male

Neurologic regression in a previously healthy child may be caused by metabolic or neurodegenerative disorders, many of which have no definitive treatment. We report a case of a previously healthy 8-year-old boy who presented with a month-long history of waxing and waning encephalopathy and acute regression, followed by seizures. Evaluation for a metabolic disorder revealed methylmalonic acidemia and hyperhomocysteinemia of the cobalamin C type due to a single, presumed homozygous pathogenic c.394 C>T mutation in the MMACHC gene. With the appropriate diet restrictions and vitamin replacement, he improved significantly and returned to his premorbid level of behavior. This case illustrates an unusual presentation of a treatable metabolic disorder and highlights the need to consider cobalamin defects in the differential diagnosis of healthy children with neurologic regression.

Cobalamin C deficiency in an adolescent with altered mental status and anorexia

Although cobalamin (cbl) C deficiency is the most common inherited disorder of vitamin B12 metabolism, the late-onset form of the disease can be difficult to recognize because it has a broad phenotypic spectrum. In this report, we describe an adolescent female exposed to unknown illicit substances and sexual abuse who presented with psychosis, anorexia, seizures, and ataxia. The patient's diagnosis was delayed until a metabolic workup was initiated, revealing hyperhomocysteinemia, low normal plasma methionine, and methylmalonic aciduria. Ultimately, cblC deficiency was confirmed when molecular testing showed compound heterozygosity for mutations (c.271dupA and c.482G>A) in the MMACHC gene. This diagnosis led to appropriate treatment with hydroxocobalamin, betaine, and folate, which resulted in improvement of her clinical symptoms and laboratory values. This patient demonstrates a previously unrecognized presentation of late-onset cblC deficiency. Although neuropsychiatric symptoms are common in late-onset disease, seizures and cerebellar involvement are not. Furthermore, anorexia has not been previously described in these patients. This case emphasizes that inborn errors of metabolism should be part of the differential diagnosis for a teenager presenting with altered mental status, especially when the diagnosis is challenging or neurologic symptoms are unexplained. Correct diagnosis of this condition is important because treatment is available and can result in clinical improvement.(1.)

Three new cases of late-onset cblC defect and review of the literature illustrating when to consider inborn errors of metabolism beyond infancy

Background

The cblC defect is a rare inborn error of intracellular cobalamin metabolism. Biochemical hallmarks are elevated homocysteine and low methionine in plasma accompanied by methylmalonic aciduria. Due to the heterogeneous clinical picture, patients with the late-onset form of the disease (onset >12 months) come to the attention of diverse medical specialists, e.g. paediatricians, neurologists, nephrologists, psychiatrists or haematologists. The report reviews the published clinical data and adds three new cases to raise awareness for this severe but often treatable disease.

Methods

The Pubmed and the Cochrane databases were searched for clinical reports on cblC patients and three unreported cases are presented to illustrate the clinical spectrum.

Results

Reports on 58 cases (30 females, 22 males, 6 = no information) and the three new cases underlined the clinical heterogeneity of the disease. Time between first symptoms and diagnosis ranged from three months to more than 20 years. Haemolytic uraemic syndrome and pulmonary hypertension were main presenting symptoms in preschool children. In older children/adolescents, psychiatric symptoms, cognitive impairment, ataxia and myelopathy were frequently observed while thromboembolic events and glomerulopathies were almost exclusively seen in adults. Brain atrophy, white matter lesions and myelopathy were frequently encountered. The majority of patients showed marked biochemical and clinical response to treatment with parenteral hydroxocobalamin combined with oral betaine, folate, carnitine and rarely methionine. The course was less favourable in late treated or untreated patients.

Conclusions

The late-onset cblC defect is a rare disease and unfortunately, diagnosis is often delayed. Raising awareness for this disorder can significantly improve patients’ outcome and perspective by timely initiation of targeted treatment. Newborn screening (NBS) for the cblC defect might be of benefit especially for late-onset patients since treatment seems efficient when initiated before irreversible organ damage. In general, inborn errors of metabolisms should be considered in unexplained medical cases at any age, especially in patients with multisystemic disease. More specifically, total homocysteine in plasma and methylmalonic acid in urine/plasma should be measured in unexplained neurologic, psychiatric, renal, haematologic and thromboembolic disease.

Clinical presentation and outcome in a series of 88 patients with the cblC defect

The cblC defect is the most common inborn error of vitamin B12 metabolism. Despite therapeutic measures, the long-term outcome is often unsatisfactory. This retrospective multicentre study evaluates clinical, biochemical and genetic findings in 88 cblC patients. The questionnaire designed for the study evaluates clinical and biochemical features at both initial presentation and during follow up. Also the development of severity scores allows investigation of individual disease load, statistical evaluation of parameters between the different age of presentation groups, as well as a search for correlations between clinical endpoints and potential modifying factors.

RESULTS

No major differences were found between neonatal and early onset patients so that these groups were combined as an infantile-onset group representing 88 % of all cases. Hypotonia, lethargy, feeding problems and developmental delay were predominant in this group, while late-onset patients frequently presented with psychiatric/behaviour problems and myelopathy. Plasma total homocysteine was higher and methionine lower in infantile-onset patients. Plasma methionine levels correlated with "overall impression" as judged by treating physicians. Physician's impression of patient's well-being correlated with assessed disease load. We confirmed the association between homozygosity for the c.271dupA mutation and infantile-onset but not between homozygosity for c.394C>T and late-onset. Patients were treated with parenteral hydroxocobalamin, betaine, folate/folinic acid and carnitine resulting in improvement of biochemical abnormalities, non-neurological signs and mortality. However the long-term neurological and ophthalmological outcome is not significantly influenced. In summary the survey points to the need for prospective studies in a large cohort using agreed treatment modalities and monitoring criteria.

Retinal Structure in Cobalamin C Disease: Mechanistic and Therapeutic Implications

PURPOSE

To describe the retinal structure in a patient with cobalamin C (cblC) disease.

METHODS

A 13-year-old male patient diagnosed with cblC disease during a perinatal metabolic screening prompted by jaundice and hypotony underwent ophthalmic examinations, electroretinography (ERG) and spectral domain optical coherence tomography (SD-OCT).

RESULTS

The patient carried a homozygous (c.271dupA) mutation in the methylmalonic aciduria and homocystinuria type C (MMACHC) gene. At age 3 months he had a normal eye exam. A pigmentary maculopathy progressed to chorioretinal atrophy from 5-10 months. ERG at 7 months was normal. A nystagmus remained stable since the age of 2 years. At age 13, visual acuity was 20/250 (right eye) and 20/400 (left eye), with a +5.00 D correction, a level of vision maintained since first measurable at age 5 years. SD-OCT showed bilateral macular coloboma-like lesions; there was also a thickened surface layer with ganglion cell layer thinning. Photoreceptor outer segment loss and thinning of the outer nuclear layer (ONL) transitioned to regions with no discernible ONL with a delaminated, thickened, inner retina.

CONCLUSIONS

A thick surface layer near the optic nerve resembling an immature retina and an initially normal macula that rapidly developed coloboma-like lesions suggest there may be an interference with retinal/foveal development in cblC, a mechanism of maculopathy that may be shared by other early onset retinal degenerations. Photoreceptor loss and inner retinal remodeling confirm associated photoreceptor degeneration.

Adult-onset eculizumab-resistant hemolytic uremic syndrome associated with cobalamin C deficiency

A 20-year-old man was hospitalized for malignant hypertension, mechanical hemolysis, and kidney failure. Kidney biopsy confirmed glomerular and arteriolar thrombotic microangiopathy. Etiologic analyses, which included ADAMTS13 activity, stool culture, complement factor proteins (C3, C4, factor H, factor I, and MCP [membrane cofactor protein]), anti-factor H antibodies, HIV (human immunodeficiency virus) serology, and antinuclear and antiphospholipid antibodies, returned normal results. Malignant hypertension was diagnosed. Ten months later, we observed a relapse of acute kidney injury and mechanical hemolysis. Considering a diagnosis of complement dysregulation-related atypical hemolytic uremic syndrome (HUS), we began treatment with eculizumab. Despite the efficient complement blockade, the patient's kidney function continued to decline. We performed additional analyses and found that the patient's homocysteine levels were dramatically increased, with no vitamin B12 (cobalamin) or folate deficiencies. We observed very low plasma methionine levels associated with methylmalonic aciduria, which suggested cobalamin C disease. We stopped the eculizumab infusions and initiated specific treatment, which resulted in complete cessation of hemolysis. MMACHC (methylmalonic aciduria and homocystinuria type C protein) sequencing revealed compound heterozygosity for 2 causative mutations. To our knowledge, this is the first report of adult-onset cobalamin C-related HUS. Considering the wide availability and low cost of the homocysteine assay, we suggest that it be included in the diagnostic algorithm for adult patients who present with HUS.

Update on hemolytic uremic syndrome: Diagnostic and therapeutic recommendations

Hemolytic uremic syndrome (HUS) is a rare disease. In this work the authors review the recent findings on HUS, considering the different etiologic and pathogenetic classifications. New findings in genetics and, in particular, mutations of genes that encode the complement-regulatory proteins have improved our understanding of atypical HUS. Similarly, the complement proteins are clearly involved in all types of thrombotic microangiopathy: typical HUS, atypical HUS and thrombotic thrombocytopenic purpura (TTP). Furthermore, several secondary HUS appear to be related to abnormalities in complement genes in predisposed patients. The authors highlight the therapeutic aspects of this rare disease, examining both “traditional therapy” (including plasma therapy, kidney and kidney-liver transplantation) and “new therapies”. The latter include anti-Shiga-toxin antibodies and anti-C5 monoclonal antibody “eculizumab”. Eculizumab has been recently launched for the treatment of the atypical HUS, but it appears to be effective in the treatment of typical HUS and in TTP. Future therapies are in phases I and II. They include anti-C5 antibodies, which are more purified, less immunogenic and absorbed orally and, anti-C3 antibodies, which are more powerful, but potentially less safe. Additionally, infusions of recombinant complement-regulatory proteins are a potential future therapy.

Cobalamin C defect presenting with isolated pulmonary hypertension

Cobalamin C (cblC) defect is the most common inborn error of vitamin B12 metabolism. Clinical features vary as does the severity of the disease. In most cases, the clinical symptoms of cblC defect tend to appear during infancy or early childhood as a multisystem disease with severe neurologic, ocular, hematologic, renal, and gastrointestinal signs. The neurologic findings are common and include hypotonia, developmental delay, microcephaly, seizures hydrocephalus, and brain MRI abnormalities. We report a case of a young boy with cblC defect, who did not undergo newborn screening, presenting at the age of 2 years with isolated pulmonary hypertension as the leading symptom. This novel way of presentation of cblC defect enlarges the spectrum of inherited diseases that must be considered in the differential diagnosis of pulmonary hypertension.