Definition of Crigler-Najjar syndrome:

Crigler-Najjar syndrome is a very rare inherited disorder in which bilirubin (a substance made by the liver) cannot be broken down.

Causes, incidence, and risk factors:

Crigler-Najjar syndrome is caused by an abnormal gene. The gene fails to make the enzyme that normally converts bilirubin into a form that can easily be removed from the body. Without this enzyme, bilirubin can build up in the body and lead to jaundice (yellow discoloration of skin and eyes) and damage to the brain, muscles, and nerves.

Crigler-Najjar (type 1) is the early-onset form of the disease. Arias syndrome (type 2) is a later-onset condition.

The syndrome runs in families (inherited). A child must get the defective gene from both parents to develop the severe form of the condition. Parents who are carriers (with just one defective gene) have about half the enzyme activity of a normal adult.