Late-onset methylmalonic acidemia and homocysteinemia (cblC disease): systematic review

INTRODUCTION

Combined methylmalonic acidemia and homocystinuria, cblC type is an inborn error of intracellular cobalamin metabolism and the most common one. The age of onset ranges from prenatal to adult. The disease is characterised by an elevation of methylmalonic acid (MMA) and homocysteine and a decreased production of methionine. The aim is to review existing scientific literature of all late onset cblC patients in terms of clinical symptoms, diagnosis, and outcome.

METHODS

A bibliographic database search was undertaken in PubMed (MEDLINE) complemented by a reference list search. We combined search terms regarding cblC disease and late onset. Two review authors performed the study selection, data extraction and quality assessment.

RESULTS

Of the sixty-five articles included in this systematic review, we collected a total of 199 patients. The most frequent clinical symptoms were neuropathy/myelopathy, encephalopathy, psychiatric symptoms, thrombotic microangiopathy, seizures, kidney disease, mild to severe pulmonary hypertension with heart failure and thrombotic phenomena. There were different forms of supplementation used in the different studies collected and, within these studies, some patients received several treatments sequentially and/or concomitantly. The general outcome was: 64 patients recovered, 78 patients improved, 4 patients did not improve, or the disease progressed, and 12 patients died.

CONCLUSIONS

Most scientific literature regarding the late onset cblC disease comes from case reports and case series. In most cases treatment initiation led to an improvement and even recovery of some patients. The lack of complete recovery underlines the necessity for increased vigilance in unclear clinical symptoms for cblC disease.

Case report: An asymptomatic mother with an inborn error of cobalamin metabolism (cblC) detected through high homocysteine levels during prenatal diagnosis

Background

The most common disorder of the intracellular cobalamin metabolism pathway is the combined methylmalonic acidemia and homocysteinemia, cblC type (cblC). There is a variation in its clinical spectrum ranging from severe neonatal-onset forms that are highly fatal to later-onset forms which are milder. In this study, the first case of an asymptomatic Chinese woman with a defect in congenital cobalamin (cblC type) metabolism at prenatal diagnosis due to elevated homocysteine level is identified.

Case presentation

The proband, a male child born to a 29-year-old G1P0 mother, admitted to local hospital with feeding disorder, intellectual disability, seizures, microcephaly, as well as heterophthalmos. The level of the urine methylmalonic was elevated. Equally found were increased blood propionylcarnitine (C3) and propionylcarnitine/free carnitine ratio (C3/C0) and decreased methionine levels. The plasma total homocysteine level was elevated at 101.04 μmol/L (normal < 15 μmol/L). The clinical diagnosis of combined methylmalonic acidemia and homocysteinemia was supported. Four years later, the mother of the boy married again and came to us for prenatal diagnosis exactly 15 weeks after her last menstrual period. Subsequently, there is an increase in the amniotic fluid methylmalonate. The level of the amniotic fluid total homocysteine was marginally high. A considerably elevated amniotic fluid C3 was equally observed. In addition, there is a respective significant increase in the plasma and urine total homocysteine at 31.96 and 39.35 μmol/L. After the sequencing of MMACHC genes, it is found that the boy, a proband carried a homozygous mutation of the MMACHC at c.658_660delAAG. While the boy's mother, she carries two mutations in MMACHC: c.658_660delAAG and c.617G>A. The fetus is a carrier of the MMACHC gene. Following the administration of routine treatment, the mother remained symptom-free in the course of pregnancy, and she gave birth to a healthy boy.

Conclusion

Variable and nonspecific symptoms characterized the cblC type of methylmalonic acidemia combined with homocysteinemia. Both biochemical assays and mutation analysis are recommended as crucial complementary techniques.

PRDX1 gene-related epi-cblC disease is a common type of inborn error of cobalamin metabolism with mono- or bi-allelic MMACHC epimutations

Background

The role of epigenetics in inborn errors of metabolism (IEMs) is poorly investigated. Epigenetic changes can contribute to clinical heterogeneity of affected patients but could also be underestimated determining factors in the occurrence of IEMs. An epigenetic cause of IEMs has been recently described for the autosomal recessive methylmalonic aciduria and homocystinuria, cblC type (cblC disease), and it has been named epi-cblC. Epi-cblC has been reported in association with compound heterozygosity for a genetic variant and an epimutation at the MMACHC locus, which is secondary to a splicing variant (c.515-1G > T or c.515-2A > T) at the adjacent PRDX1 gene. Both these variants cause aberrant antisense transcription and cis-hypermethylation of the MMACHC gene promotor with subsequent silencing. Until now, only nine epi-cblC patients have been reported.

Methods

We report clinical/biochemical assessment, MMACHC/PRDX1 gene sequencing and genome-wide DNA methylation profiling in 11 cblC patients who had an inconclusive MMACHC gene testing. We also compare clinical phenotype of epi-cblC patients with that of canonical cblC patients.

Results

All patients turned out to have the epi-cblC disease. One patient had a bi-allelic MMACHC epimutation due to the homozygous PRDX1:c.515-1G > T variant transmitted by both parents. We found that the bi-allelic epimutation produces the complete silencing of MMACHC in the patient’s fibroblasts. The remaining ten patients had a mono-allelic MMACHC epimutation, due to the heterozygous PRDX1:c.515-1G > T, in association with a mono-allelic MMACHC genetic variant. Epi-cblC disease has accounted for about 13% of cblC cases diagnosed by newborn screening in the Tuscany and Umbria regions since November 2001. Comparative analysis showed that clinical phenotype of epi-cblC patients is similar to that of canonical cblC patients.

Conclusions

We provide evidence that epi-cblC is an underestimated cause of inborn errors of cobalamin metabolism and describe the first instance of epi-cblC due to a bi-allelic MMACHC epimutation. MMACHC epimutation/PRDX1 mutation analyses should be part of routine genetic testing for all patients presenting with a metabolic phenotype that combines methylmalonic aciduria and homocystinuria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-021-01117-2.

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.

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.