There is plenty of canalicular multi-drug resistant protein which causes bilirubin transfer to bile canaliculi. An isoform of this protein is localized to the lateral hepatocyte membrane, allowing transport of glucuronide and glutathione conjugates back into the blood.
Analysis of urine pophyrins show a normal level of coproporphirin but the I isomer accounts for 80% of the total (normally 25%)
Liver will present with dark pink or black appearance due to pigment accumulation.
The conjugated hyperbilirubinemia is a result of defective endogenous and exogenous transfer of anionic conjugates from hepatocytes into the bile. Pigment deposition in lysosomes causes the liver to turn black.
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 III being 3-4x higher then coproporphyrin I.
DJS has a defect in the multispecific anion transporter (cMOAT) gene (ABC transporter superfamily).
Likely a loss of function mutation, since the mutation affects the cytoplasmic / binding domain.
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 contraceptive and pregnancy may lead to overt jaundice and icterus (yellowing of the eyes)
^ abc Suzanne M Carter, MS. eMedicine: Dubin-Johnson Syndrome. January 9, 2007. http://www.emedicine.com/ped/topic621.htm