Positive newborn screen for methylmalonic aciduria identifies the first mutation in TCblR/CD320, the gene for cellular uptake of transcobalamin-bound vitamin B(12).
In our cohort, two children were affected by methylmalonic acidemia and suffered acute basal ganglia lesions, while the other two carried a pathogenic mutation in GNAO1 gene.
Several genome-wide association studies have discovered novel loci at chromosome 12q24, which includes mevalonate kinase (MVK), methylmalonic aciduria (cobalamin deficiency) cbIB type (MMAB), and potassium channel tetramerization domain-containing 10 (KCTD10), all of which influence HDL-cholesterol concentrations.
The prevalence of each IEM ranged from 1/401,660 to 1/19,128, while phenylketonuria (PKU) (1/19,128) and Mild hyperphenylalaninemia (M-HPA) (1/19,128) were the most common IEMs, followed by primary carnitine uptake defect (PCUD) (1/26,777), SCADD (1/28,690), hypermethioninemia (H-MET) (1/30,893), 3-MCCD (1/33,412) and methylmalonic acidemia (MMA) (1/40,166).
To our knowledge, this is the first report of an adult patient with <i>MCEE</i> mutations and MMA-uria, thus adding novel data to the possible phenotypical spectrum of MCE deficiency.
We conclude that the patient's MCEE defect was responsible for the mild methylmalonic aciduria, confirming a partial requirement for the enzymatic activity in humans.
Methylmalonic acidemia (MMA) is an autosomal recessive inherited disorder caused by complete or partial deficiency of the enzyme methylmalonyl-CoA mutase (mut0 enzymatic subtype or mut- enzymatic subtype, respectively); a defect in the transport or synthesis of its cofactor, adenosyl-cobalamin (cblA, cblB, or cblD-MMA); or deficiency of the enzyme methylmalonyl-CoA epimerase.
The C. elegans mce-1 deletion mutant demonstrates for the first time that a lesion at the epimerase step of methylmalonyl-CoA metabolism can functionally impair flux through the methylmalonyl-CoA mutase pathway and suggests that malfunction of MCEE may cause methylmalonic acidemia in humans.