Branched chain ketoaciduria, or maple syrup urine disease (MSUD), is a metabolic disorder in which an enzyme deficiency allows branched-chain(枝分かれ鎖、1つ以上の側鎖をもつ原子の鎖)amino acids to build up in the blood and urine. Often diagnosed in infancy, the condition gets its name from the distinctive sweet odor - similar to that of maple syrup or burnt caramel - of the sufferer's urine. If left untreated, MSUD can cause severe brain damage or death.