Crigler-najjar syndrome, is an inherited metabolic disorder in which bilirubin metabolism is impaired, due to a mutation in the UGT1A1 (UDP glucuronosyltransferase 1 family, polypeptide A1) gene. As a result of invalid UGT1A1 enzyme function, bilirubin is not properly eliminated from the body; its accumulation causes brain, muscle, and liver damage.