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Methylmalonic Aciduria and Homocystinuria, Cobalamin C (cblC) Type
MMACHC
gene Methylmalonic aciduria and homocystinuria, cblC type, is a defect in B12 metabolism. This autosomal recessive disorder is due to mutations in the MMACHC gene, that cause decreases in adenosylcobalamin and methylcoblamin and deficient activity of both methylmalonyl-CoA mutase and methionine synthase/methyltetrahydrofolate: homocysteine methyltransferase. Patients have megaloblastic and macrocytic anemia, failure to thrive, microcephaly, lethargy and feeding difficulties. Neurologic symptoms may include hypotonia, seizures, developmental delay, ataxia and optic atrophy. Later onset cases may present with neurologic symptoms such as anorexia, irritability, fatigue, myelopathy or dementia. Other complications are mental retardation, microcephaly, retinal degeneration, pigmentary retinopathy, microangiopathy and skin lesions. In one large study, sequencing of the MMACHC gene identified mutations in both alleles in 95% of patients with methylmalonic acidemia and homocystinuria, cblC Type; in approximately 2.5% of patients a single mutation was identified and in approximately 2.5% no mutation was identified on either allele.
Testing is performed on genomic DNA obtained from a blood sample (2mL for infants, 5mL for adults in EDTA) or from buccal brushes provided by GeneDx (not accepted on infants). If sequencing identifies a mutation on only one allele of the MMACHC gene, and if clinically indicated, reflex deletion/duplication testing (ExonArrayDx) will be performed at no additional charge to evaluate for a deletion/duplication of one or more exons of this gene. Carrier testing of relatives and prenatal diagnosis in at-risk pregnancies are available once the mutations in a family have been defined.
Information Sheet, including prices and CPT codes
Consent Document
Genetic Test Sample Submission Form (Test Requisition Form) including Payment Options
Methylmalonic acidemia and homocystinuria, cblC type, Methylmalonic aciduria and homocystinuria, vitamin B12-responsive, vitamin B12 metabolic defect with combined deficiency of methylmalonyl-CoA mutase and homocysteine: methyltetrahydrofolate methyltransferase, inborn error of metabolism, biochemical, cobalamin, newborn screening
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