Sinusoidal blood side
OATP1B1 and OATP1B3 normally reclaim conjugated bilirubin and organic anions.
GI
Dubin-Johnson Syndrome
Two benign direct bilirubin disorders split at the hepatocyte exit and re-entry doors.
- Differentiate Dubin-Johnson and Rotor syndromes from unconjugated bilirubin disorders and acquired cholestasis.
- Connect ABCC2 or MRP2 canalicular export failure with black liver and SLCO1B1 or SLCO1B3 reuptake failure with Rotor syndrome.
- Interpret total urinary coproporphyrin and isomer I patterns while preserving the benign management boundary.
Bilirubin route
Follow the pigment without skipping a compartment
The route distinguishes production, transport, conjugation, excretion, and downstream clues.
Quick check
A 25-year-old has intermittent jaundice with predominantly conjugated bilirubin and normal AST, ALT, alkaline phosphatase, and GGT. During unrelated surgery, the liver appears dark brown-black.
Which diagnosis is most likely?
Reason it through
- Which bilirubin fraction dominates?The conjugated fraction.
- Are the liver enzymes signaling injury?No; the enzymes are normal.
- What gross clue separates the two benign transport defects?The dark brown-black liver points to Dubin-Johnson syndrome.
Put Dubin-Johnson beside Rotor
Both are benign conjugated hyperbilirubinemias, but they disrupt opposite membrane routes.
Dubin-Johnson syndrome results from biallelic ABCC2 variants that impair the canalicular MRP2 export of conjugated bilirubin and other organic anions into bile.
Rotor syndrome results from combined loss of the sinusoidal uptake transporters OATP1B1 and OATP1B3, impairing hepatic uptake and reuptake of conjugated bilirubin. Both usually have normal liver enzymes and no hemolysis or progressive liver disease.
Compare the two transport defects.
Canalicular MRP2 export failure, black hepatic pigment, and normal total urinary coproporphyrin with marked isomer I predominance.
Sinusoidal OATP1B1 and OATP1B3 uptake failure, no black pigment, and increased total urinary coproporphyrin.
Mild predominantly conjugated hyperbilirubinemia, bilirubinuria, normal enzymes, benign course, and no specific therapy.
Dubin cannot export; Rotor cannot recapture.
Follow conjugated bilirubin through a hepatocyte
The location of the broken transporter explains the laboratory pattern.
After UGT1A1 conjugates bilirubin, MRP2 normally exports the conjugate across the canalicular membrane into bile. Some conjugated bilirubin returns to plasma and is normally reclaimed across the sinusoidal membrane by OATP1B1 and OATP1B3.
MRP2 failure causes Dubin-Johnson syndrome. Loss of both OATP transporters prevents hepatic reuptake and storage, producing Rotor syndrome and a larger urinary loss of coproporphyrins.
Order the normal route and its two failure points.
- Conjugate bilirubinUGT1A1 makes bilirubin water soluble inside the hepatocyte.
- Export across the canaliculusMRP2 moves conjugated bilirubin toward bile.
- Allow a small plasma refluxA fraction of conjugated bilirubin returns to sinusoidal blood.
- Reclaim at the sinusoidOATP1B1 and OATP1B3 take conjugates back into hepatocytes.
- Excrete through bile or urineThe balance of transport determines plasma and urinary patterns.
Read the coproporphyrin fingerprint
The isomer I percentage rises in both disorders, but only Rotor markedly raises total output.
Normal urine contains roughly 25 percent coproporphyrin I. Rotor syndrome shifts the fraction to about 65 percent and increases total coproporphyrin 2.5- to 5-fold.
Dubin-Johnson syndrome usually keeps total coproporphyrin near normal while shifting more than 80 percent to isomer I.
Place the patterns on an isomer I scale.
Let urinary coproporphyrin break the tie
Total output and isomer distribution answer different questions.
In Dubin-Johnson syndrome, total urinary coproporphyrin is usually normal, but coproporphyrin isomer I rises to more than 80 percent of the total.
In Rotor syndrome, total urinary coproporphyrin is increased about 2.5- to 5-fold, while isomer I is usually around 65 percent. Normal urine contains mostly isomer III, with isomer I near 25 percent.
Select the Dubin-Johnson urinary pattern.
Dubin changes the ratio; Rotor changes the ratio and the total.
Name the membrane before the syndrome
Canalicular and sinusoidal transport face opposite directions.
The canalicular membrane faces bile and contains MRP2. A defect here traps export substrates and promotes reflux of conjugated bilirubin to plasma.
The sinusoidal membrane faces blood and contains OATP1B1 and OATP1B3. Loss here prevents hepatic uptake and reuptake, leaving conjugates and coproporphyrins in plasma for renal excretion.
Place each finding on the hepatocyte.
Hepatocyte cytoplasm
Conjugation remains intact in both syndromes.
Canalicular bile side
MRP2 exports conjugated bilirubin; failure defines Dubin-Johnson syndrome.
Centrilobular lysosomes
Coarse dark pigment accumulates in Dubin-Johnson syndrome and creates the black liver.
Protect the benign boundary
The diagnostic win is avoiding both missed cholestasis and unnecessary treatment.
Before labeling an inherited benign transport disorder, confirm isolated predominantly conjugated hyperbilirubinemia, normal liver enzymes and synthetic function, and absence of hemolysis, obstruction, drug injury, or systemic disease.
Neither Dubin-Johnson nor Rotor syndrome requires bilirubin-lowering therapy or routine liver biopsy. Jaundice can fluctuate with illness, pregnancy, or estrogen exposure in Dubin-Johnson syndrome; new pruritus, enzyme elevation, pale stools, weight loss, or impaired synthetic function requires a fresh evaluation rather than attribution to the inherited diagnosis.
Reveal the management decision for each branch.
- Classic isolated pattern
Confirm with focused laboratory or genetic testing and reassure.
Both disorders have a benign course.
- Black liver found incidentally
Use bilirubin fraction and coproporphyrins before assuming toxic or infiltrative disease.
The gross appearance can be dramatic despite preserved function.
- Atypical liver injury pattern
Evaluate obstruction, hepatitis, medication effects, and other cholestatic disease.
The inherited label does not explain abnormal enzymes or synthetic failure.
- Pregnancy or estrogen-associated flare
Reassess the fraction and liver tests, then manage conservatively if the benign pattern remains intact.
A known syndrome should not erase obstetric or hepatobiliary differentials.
Benign is a conclusion after the pattern fits, not permission to ignore new injury.
Key laboratory clue
Choose the compartment that explains the pattern
Localize the defect in bilirubin handling before naming a syndrome.
Which diagnosis is most likely?
- Key finding. A 25-year-old has intermittent jaundice with predominantly conjugated bilirubin and normal AST, ALT, alkaline phosphatase, and GGT. During unrelated surgery, the liver appears dark brown-black.
- Answer. Dubin-Johnson syndrome
- Why. ABCC2 or MRP2 dysfunction causes benign conjugated hyperbilirubinemia and characteristic dark hepatic pigment.
- Board rule. Direct bilirubin plus a black liver is the Dubin-Johnson signature.
Stage 1 of 3: Overview
Overview
Dubin-Johnson Syndrome
The location of the broken transporter explains the laboratory pattern.
Interpret the bilirubin patterns
Five patients test black liver, transporter direction, coproporphyrin totals, fraction-based differential diagnosis, and benign management.
Cross out the wrong compartment and highlight the clue that localizes bilirubin handling. Each case follows the route step by step.
A 28-year-old has lifelong mild direct hyperbilirubinemia with normal enzymes. A liver biopsy performed elsewhere shows normal architecture with coarse dark centrilobular pigment.
Which molecular defect is most likely?
Reason it through
- Is conjugation intact?Yes; the excess bilirubin is direct.
- Which membrane must fail?The canalicular export membrane.
- What transporter sits there?MRP2, encoded by ABCC2.
Is conjugation intact?Which membrane must fail?
- Is conjugation intact?Yes; the excess bilirubin is direct.
- Which membrane must fail?The canalicular export membrane.
- What transporter sits there?MRP2, encoded by ABCC2.
A teenager has mild conjugated hyperbilirubinemia, normal liver enzymes, no hemolysis, and a normal-colored liver. Total urinary coproporphyrin is four times normal and 66 percent is isomer I.
Which diagnosis is most likely?
Reason it through
- What does the normal-colored liver remove?It removes the classic Dubin-Johnson pigment clue.
- What happened to total coproporphyrin?It rose four-fold.
- Which fraction completes the pattern?Isomer I near 65 percent supports Rotor syndrome.
What does the normal-colored liver remove?What happened to total coproporphyrin?
- What does the normal-colored liver remove?It removes the classic Dubin-Johnson pigment clue.
- What happened to total coproporphyrin?It rose four-fold.
- Which fraction completes the pattern?Isomer I near 65 percent supports Rotor syndrome.
A 32-year-old with isolated direct hyperbilirubinemia has normal total urinary coproporphyrin, but 88 percent is coproporphyrin I.
Which diagnosis is most likely?
Reason it through
- Did total coproporphyrin rise?No; it remains normal.
- Did the isomer ratio shift?Yes; isomer I dominates.
- Which syndrome owns that combination?Dubin-Johnson syndrome.
Did total coproporphyrin rise?Did the isomer ratio shift?
- Did total coproporphyrin rise?No; it remains normal.
- Did the isomer ratio shift?Yes; isomer I dominates.
- Which syndrome owns that combination?Dubin-Johnson syndrome.
A child with confirmed biallelic loss involving SLCO1B1 and SLCO1B3 has intermittent jaundice and normal liver enzymes.
Which transport process is impaired?
Reason it through
- Which membrane contains OATP transporters?The blood-facing sinusoidal membrane.
- Which direction do they move substrates?From sinusoidal blood into hepatocytes.
- What syndrome follows their combined loss?Rotor syndrome.
Which membrane contains OATP transporters?Which direction do they move substrates?
- Which membrane contains OATP transporters?The blood-facing sinusoidal membrane.
- Which direction do they move substrates?From sinusoidal blood into hepatocytes.
- What syndrome follows their combined loss?Rotor syndrome.
A pregnant patient with known Dubin-Johnson syndrome develops more visible jaundice. Direct bilirubin is mildly elevated, but AST, ALT, alkaline phosphatase trend, GGT, INR, and ultrasound are reassuring and she has no pruritus.
What is the most appropriate next step?
Reason it through
- Did the bilirubin fraction change category?No; it remains the known direct pattern.
- Is there evidence of liver injury or failure?No; enzymes, INR, symptoms, and imaging are reassuring.
- What does pregnancy do in this syndrome?It can increase the visibility of otherwise benign jaundice.
Did the bilirubin fraction change category?Is there evidence of liver injury or failure?
- Did the bilirubin fraction change category?No; it remains the known direct pattern.
- Is there evidence of liver injury or failure?No; enzymes, INR, symptoms, and imaging are reassuring.
- What does pregnancy do in this syndrome?It can increase the visibility of otherwise benign jaundice.
Rapid review
Three questions to check
Which diagnosis is most likely?
Dubin-Johnson syndrome. ABCC2 or MRP2 dysfunction causes benign conjugated hyperbilirubinemia and characteristic dark hepatic pigment.
Is conjugation intact?
Yes; the excess bilirubin is direct.
Which membrane must fail?
The canalicular export membrane.
Medically reviewed
Fatima Ali, DO
PGY-1 Resident Physician in Psychiatry
University Hospitals, Columbia
DO from Kansas City University
Resident physician and founding medical reviewer at Bone Wizardry, focused on clinical accuracy, clear diagnostic reasoning, and practical board-oriented teaching across the curriculum.
Languages: English, Urdu
Primary reviewerFull physician profile
Medically reviewed
Sources
- Rotor Syndrome2025
- Dubin-Johnson and Rotor Syndromes: A Review and Update of Pathophysiological Mechanisms2026
- Dubin-Johnson Syndrome2023
Bone Wizardry is a study resource for medical students. It is not medical advice.