[1] These conditions are conventionally split into conjugated or unconjugated hyperbilirubinemias based on where the enzyme mutation occurs in bilirubin metabolism.

[1] Unconjugated bilirubin is byproduct of red blood cell breakdown from the spleen which is not water soluble and is transported via albumin to the liver.

Once in the liver it becomes conjugated and water soluble and easier to excrete via the gastrointestinal tract in bile.

[3] Hyperbilirubinemia can cause a yellowing of the skin called jaundice depending on the level of bilirubin in the blood.

[3] Depending on a patient's genetic mutation they may be asymptomatic, have severe symptoms requiring hospitalization or experience death.

[1] Depending on the type of hereditary hyperbilirubinemia, symptoms can be worsened when an additional cause of increased red blood cell turnover occurs, as these patients have a decreased ability to process bilirubin.

Gilbert Syndrome is a partial reduction in UGT1A1's activity which causes transient hyperbilirubinemia during various stressors, like fasting or acute illness.

Dubin-Johnson syndrome is caused by mutations in ABCC2/MRP2 which usually transports conjugated bilirubin out of the liver cell.

Due to many of the conditions having multiple mutations which can cause the enzyme deficiencies, gene analysis and genetic sequencing may be required.