Methylmalonic Acid

Methylmalonate (methylmalonic acid) is measured as a second-tier assay when abnormal propionyl carnitine or methionine concentrations are identified in a primary newborn screening. Methylmalonic acidemia (MMA) and propionic acidemia (PA) are defects of propionate metabolism caused by deficiencies in methylmalonyl-CoA mutase and propionyl-CoA carboxylase, respectively. The clinical phenotype of both conditions includes vomiting, hypotonia, lethargy, apnea, hypothermia, and coma. The biochemical phenotype for MMA includes elevated methylmalonic acid, propionyl carnitine and methylcitric acid, while patients with PA have elevated propionyl carnitine and methylcitric acid with normal methylmalonic acid concentrations as the enzymatic defect is upstream of methylmalonic-CoA mutase.

Unit

mcmol/L