Dubin-Johnson syndrome
Overview
Dubin-Johnson syndrome is an autosomal recessive disorder which causes an increase of conjugated bilirubin without elevation of liver enzymes (ALT, AST). This condition is associated with a defect in the ability of hepatocytes to secrete conjugated bilirubin into the bile. It is usually asymptomatic but may be diagnosed in early infancy based on laboratory tests.
Causes
DJS is an autosomal recessive disorder that is caused by a mutation in the gene responsible for the cMOAT protein.
Diagnosis
A hallmark of DJS is the unusual ratio between the byproducts of heme biosynthesis. Unaffected subjects have a coproporphyrin III to coproporphyrin I ratio of approximately 3-4:1. In patients with DJS, this ratio is inverted with coproporphyrin I being 3-4x higher than coproporphyrin III. Analysis of urine porphyrins show a normal level of coproporphyrin but the I isomer accounts for 80% of the total (normally 25%). In post-mortem autopsy, the liver will have a dark pink or black appearance due to pigment accumulation.
Prognosis
Prognosis is good, and treatment of this syndrome is usually unnecessary. Most patients are asymptomatic and have normal life spans. Some neonates will present with cholestasis. Oral contraceptives and pregnancy may lead to overt jaundice and icterus (yellowing of the eyes).