Congenital Hyperbilirubinemia

Classification Overview

Unconjugated Hyperbilirubinemias

1. Gilbert's Syndrome

• Prevalence: Most common — affects 3–7% of the population; male:female ratio ~1.5–7:1
• Genetics: Autosomal recessive; promoter mutation in UGT1A1 (TA repeat in TATA box: UGT1A1*28 allele) reduces enzyme expression
• Pathophysiology: Reduced hepatic UDP-glucuronosyltransferase (UDPGT) activity → impaired bilirubin conjugation
• Bilirubin level: Serum total bilirubin almost always <6 mg/dL (103 µmol/L); fluctuates
• Triggers for jaundice: Fasting, stress, illness, alcohol, strenuous exercise, surgery
• Clinical features: Mild intermittent jaundice (scleral icterus most common); no hemolysis, no liver disease
• Diagnosis:
  • Isolated unconjugated hyperbilirubinemia
  • Normal LFTs, CBC, reticulocyte count, LDH
  • Genetic testing for UGT1A1*28 can confirm
  • Caloric restriction test (bilirubin rises with fasting) — largely historical
• Management: Benign; no treatment required. Patient reassurance is key. Caution with drugs metabolized by UGT1A1 (e.g., irinotecan — risk of toxicity).

2. Crigler-Najjar Syndrome

• Phototherapy: 10–16 hours/day under blue-spectrum lights; mandatory from birth; efficacy decreases with age as skin thickens
• Liver transplantation: Definitive cure — corrects the enzymatic defect (UGT1A1 is primarily hepatic); ideally performed before irreversible neurologic damage (~age 10–15 before phototherapy becomes less effective)
• Plasmapheresis: Bridge therapy during acute bilirubin crises
• Gene therapy: Under active investigation (AAV-based UGT1A1 delivery)

• Phenobarbital (enzyme inducer) — reduces bilirubin significantly
• Phototherapy usually not needed long-term
• Liver transplant rarely required

Conjugated Hyperbilirubinemias

3. Dubin-Johnson Syndrome

• Defect: Loss-of-function mutations in MRP2 (ABCC2) — the canalicular multispecific organic anion transporter responsible for secreting conjugated bilirubin into bile
• Inheritance: Autosomal recessive
• Bilirubin: Predominantly direct (conjugated); total bilirubin typically 2–5 mg/dL, occasionally higher
• Clinical features:
  • Chronic or intermittent mild jaundice; usually benign
  • May worsen with oral contraceptives, pregnancy, or illness
  • Liver appears grossly black/dark due to melanin-like pigment accumulation in hepatocytes (pathognomonic on biopsy)
  • Hepatosplenomegaly absent; LFTs otherwise normal
• Diagnostic clue: Urinary coproporphyrin pattern — total urinary coproporphyrin is normal, but >80% is coproporphyrin I (normally coproporphyrin III predominates)
• BSP test (bromsulphthalein — historical): Characteristic secondary rise at 90 min
• Prognosis: Excellent; no treatment needed

4. Rotor Syndrome

• Defect: Loss-of-function mutations in both SLCO1B1 and SLCO1B3 — hepatic sinusoidal uptake transporters (OATP1B1 and OATP1B3) that recapture conjugated bilirubin regurgitated into plasma
• Inheritance: Autosomal recessive
• Bilirubin: Mixed conjugated and unconjugated; mild elevation
• Clinical features:
  • Mild chronic jaundice; otherwise asymptomatic
  • Liver biopsy: normal (no pigment — key distinction from Dubin-Johnson)
  • Gallbladder visualizes normally on oral cholecystography (vs. Dubin-Johnson: poor visualization)
• Diagnostic clue: Total urinary coproporphyrin is elevated (2–5× normal), with a normal coproporphyrin I:III ratio (~65% coproporphyrin I)
• Prognosis: Excellent; no treatment needed

Comparison: Dubin-Johnson vs. Rotor

Key Points for Clinical Practice

1. Isolated unconjugated hyperbilirubinemia with normal LFTs and no hemolysis in a young person = Gilbert's syndrome until proven otherwise.
2. Crigler-Najjar Type I is a neonatal emergency — presents as severe jaundice in the first days of life, requires phototherapy immediately and liver transplant planning.
3. Phenobarbital response distinguishes Crigler-Najjar Type II from Type I.
4. Conjugated hyperbilirubinemia in the absence of hepatocellular disease or biliary obstruction points to Dubin-Johnson or Rotor — differentiated by urinary coproporphyrin pattern and liver biopsy.
5. All congenital hyperbilirubinemias except Crigler-Najjar Type I carry an excellent prognosis and do not progress to cirrhosis or liver failure.