Biochem/physiol Actions

3-Methylglutaconic aciduria (MGCA) is a group of metabolic disorders characterized by increased urinary excretion of 3-methylglutaconic acid and 3-methylglutaric acid. Five distinct forms of MGCA have been recognized. MGCA type 1 is caused by primary deficiency of the mitochondrial enzyme 3-methylglutaconyl-CoA hydratase (3-MGCH), resulting in a block of leucine degradation. In all other types, the activities of 3-MGCH and other enzymes of leucine degradation are normal and the MGCA is thought to be secondary to a defect in another pathway. MGCA type 2, also known as Barth syndrome, is an X-linked cardiomyopathy associated with skeletal myopathy, neutropenia, and growth retardation. MGCA type 3, also referred to as Costeff optic atrophy syndrome, is an autosomal recessive disorder caused by mutations in the gene OPA3. It is characterized by early-onset bilateral optic atrophy, later-onset extrapyramidal dysfunction. MGCA type 5 caused by mutation in the DNAJC19 gene, is characterized by early-onset dilated cardiomyopathy with conduction defects, nonprogressive cerebellar ataxia, testicular dysgenesis, and growth failure. MGCA type 4 is the unclassified type, which includes all other patients with MGCA.