3-methylcrotonyl-CoA carboxylase deficiency (3-MCCD) is an inherited disorder of leucine metabolism characterized by a highly variable clinical picture ranging from metabolic crisis in infancy to asymptomatic adults. The disease is 3-methylcrotonyl-CoA carboxylase deficiency (MONDO_0018950). Also known as: 3-MCC deficiency, 3-methylcrotonylglycinuria, 3MCC deficiency, BMCC deficiency, MCC deficiency, MCCD, Methylcrotonyl-CoA carboxylase deficiency.