Causes

An abnormal gene you inherit from your parents causes Gilbert's syndrome. The gene normally controls an enzyme that helps break down bilirubin in your liver. When you have an ineffective gene, your blood contains excess amounts of bilirubin because your body doesn't produce enough of the enzyme.

How the body normally processes bilirubin

Bilirubin is a yellowish pigment made when your body breaks down old red blood cells. Bilirubin travels through your bloodstream to the liver, where the enzyme breaks down the pigment and removes it from the bloodstream.

The bilirubin passes from the liver into the intestines with bile. It's then excreted in stool. A small amount of bilirubin remains in the blood.

How the abnormal gene is passed through families

The abnormal gene that causes Gilbert's syndrome is common. Many people carry one copy of this gene. In most cases, two abnormal copies are needed to cause Gilbert's syndrome.