Maple Syrup Urine Disease (MSUD), also called branched-chain ketoaciduria, is rare, genetic disorder which is characterized by a deficiency of enzymes required to metabolize certain amino acids. These amino acids and their many metabolites abnormally accumulate in the cells and fluids of the body, causing symptoms including lethargy, irritability, convulsions, poor appetite and a maple syrup odor within the earwax, sweat and urine of affected people.