Meta-Biol

• Pathways

Bilirubin (BIL) is a breakdown product of heme, causing death if allowed to accumulate in the blood. It is highly lipophilic and thus requires conjugation to become more water soluble to aid excretion. UGT1A1 and 4 are the only enzymes that transfer glucuronic acid (GlcA) to bilirubin to form either its monoglucuronide (BMG) or diglucuronide (BDG) conjugate. Defects in UGT1A4 can cause hyperbilirubinemia syndromes ranging from mild forms such as Gilbert syndrome (GILBS; MIM:143500) to the more severe Crigler-Najjar syndromes 1 and 2 (CN1, CN2; MIM:218800 and MIM:606785). A mutation causing the severest form, CN1, is S376F (Bosma et al. 1992).