This gene encodes a member of the aldehyde dehydrogenase protein family. The encoded enzyme is a mitochondrial methylmalonate semialdehyde dehydrogenase that plays a role in the valine and pyrimidine catabolic pathways. This enzyme catalyzes the irreversible oxidative decarboxylation of malonate and methylmalonate semialdehydes to acetyl- and propionyl-CoA. Mutations in the human gene result in Methylmalonate Semialdehyde Dehydrogenase Deficiency, characterized by elevated beta-alanine, 3-hydroxypropionic acid, and both isomers of 3-amino and 3-hydroxyisobutyric acids in urine organic acids. Alternate splicing results in multiple transcript variants encoding different isoforms. [provided by RefSeq, Sep 2015]