"methylmalonic acid" noun a dicarboxylic acid isomeric with succinic acid, (CH₃)CH(COOH)₂.
"methylmalonic aciduria" noun the presence of an abnormally large amount of methylmalonic acid in the urine, especially as a manifestation of an inborn error of metabolism; an instance of this.
"methylmalonic acidaemia" noun any of several inherited metabolic disorders characterized by the presence of an abnormally large quantity of methylmalonic acid in the blood and urine.
Late 19th century; earliest use found in Journal of the Chemical Society. From methyl + malonic, after German Methylmalonsäure methylmalonic acid.