Persistent, severe (> 20 mg/dl) unconjugated bilirubinemia presenting in 1st few days of life; kernicterus occurs without aggressive treatment by continuous phototherapy or liver transplantation. Cause is defect in glucuronyl transferase; absence of bilirubin diglucuronide is pathognomonic. No decrease in serum bilirubin is seen after phenobarbital administration.