A 28-year-old man evaluated for mild jaundice has conjugated hyperbilirubinemia (total 3.2 mg/dL, direct 2.4 mg/dL), otherwise normal liver enzymes and no hemolysis. Liver biopsy shows dark brown-black pigmentation of hepatocytes. He is asymptomatic and has a normal life expectancy. The underlying defect is:

• A Defect of UGT1A1 causing impaired bilirubin conjugation
• B Defect of the canalicular multidrug resistance-associated protein 2 (MRP2) transporter ✓
• C Organic anion transport defect without hepatic pigmentation
• D Defect of bile salt export pump causing progressive cholestasis

Explanation

Dubin-Johnson syndrome is caused by mutation of ABCC2 encoding MRP2, the apical canalicular organic anion transporter, leading to benign conjugated hyperbilirubinemia with characteristic deposition of dark epinephrine-derived pigment giving a black liver. Prognosis is excellent. Option C describes Rotor syndrome, which is biochemically similar but lacks the pigment. UGT1A1 defects cause unconjugated hyperbilirubinemias such as Gilbert and Crigler-Najjar syndromes, and bile salt export pump defects cause progressive familial intrahepatic cholestasis.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.