Inherited Hyperbilirubinaemia

Inherited hyperbilirubinaemias are genetically determined disorders of bilirubin metabolism. Gilbert syndrome and Crigler-Najjar syndrome cause unconjugated hyperbilirubinaemia through deficient or absent hepatic bilirubin conjugation. Dubin-Johnson syndrome and Rotor syndrome cause conjugated hyperbilirubinaemia through impaired hepatocellular excretion of already-conjugated bilirubin.

Accurate distinction between these conditions, and from acquired causes of hyperbilirubinaemia, matters for prognosis. Clinical significance ranges from the entirely benign Gilbert syndrome to the potentially severe, neurologically significant Crigler-Najjar syndrome type one.

Classification and pathophysiology

• Gilbert syndrome is the commonest of the group by a substantial margin. Reduced activity of the hepatic enzyme UDP-glucuronosyltransferase reflects a common genetic variant in the promoter region of the relevant gene. It produces mild, fluctuating unconjugated hyperbilirubinaemia without hepatocellular damage or clinically significant consequence.
• Crigler-Najjar syndrome results from more severe deficiency of the same enzyme.
  • Type one reflects complete, absent enzyme activity. It produces severe, persistent unconjugated hyperbilirubinaemia with substantial risk of kernicterus if inadequately managed.
  • Type two reflects partial, residual enzyme activity. It produces a milder, though still clinically significant, hyperbilirubinaemia with generally preserved response to specific pharmacological treatment.
• Dubin-Johnson syndrome results from a defect in the canalicular transport protein that excretes conjugated bilirubin and other organic anions from the hepatocyte into bile. It produces mild, chronic conjugated hyperbilirubinaemia. The liver shows a characteristic, clinically inconsequential dark pigmentation on macroscopic or histological examination.
• Rotor syndrome results from a distinct, functionally related defect affecting hepatic storage and excretion of conjugated bilirubin. It produces a pattern of mild conjugated hyperbilirubinaemia similar to Dubin-Johnson syndrome. It lacks the characteristic hepatic pigmentation, which is an important distinguishing feature between these two otherwise clinically similar conditions.

• Gilbert syndrome typically presents in adolescence or early adulthood with mild, intermittent jaundice. It is often first noticed incidentally or after an identifiable precipitant, including intercurrent illness, fasting, dehydration, or physical exertion. The individual is otherwise entirely well, with no other symptom or sign of liver disease.
• Crigler-Najjar syndrome type one presents in the neonatal period with severe, persistent jaundice. Very high, sustained unconjugated bilirubin levels reflect the complete enzyme deficiency, and the risk of kernicterus is substantial if management is inadequate.
• Crigler-Najjar syndrome type two presents with a milder, though still clinically apparent, pattern of persistent jaundice. Kernicterus risk is generally lower, given the partial, residual enzyme activity.
• Dubin-Johnson syndrome and Rotor syndrome typically present with mild, chronic jaundice, often first apparent in adolescence or early adulthood. Again, there is no other symptom or sign of underlying liver disease or hepatocellular dysfunction.
• The shared, defining clinical feature across the group is isolated hyperbilirubinaemia without other biochemical or clinical evidence of hepatocellular injury or dysfunction. Liver function tests beyond bilirubin, and liver synthetic function, remain entirely normal. This is an important, reassuring distinction from acquired hepatobiliary disease.

• Diagnosis is established through the characteristic clinical pattern of isolated, fluctuating hyperbilirubinaemia in an otherwise well individual. Relevant acquired causes of hyperbilirubinaemia must be fully excluded, including haemolysis, viral hepatitis, and biliary obstruction.
• The bilirubin fraction elevated, unconjugated versus conjugated, directs the subsequent diagnostic pathway. Unconjugated hyperbilirubinaemia prompts consideration of Gilbert or Crigler-Najjar syndrome. Conjugated hyperbilirubinaemia prompts consideration of Dubin-Johnson or Rotor syndrome.
• Gilbert syndrome is generally diagnosed clinically, given the characteristic, mild, fluctuating pattern with entirely normal liver function tests and imaging. Genetic testing is available but not routinely required, given the benign, clinically inconsequential nature of the diagnosis.
• Crigler-Najjar syndrome diagnosis relies on the characteristic severity of presentation, with genetic testing confirming the specific underlying mutation. Liver biopsy was historically used to assess residual enzyme activity but has been largely superseded by genetic testing in contemporary practice.
• Dubin-Johnson syndrome may be supported by a characteristic urinary coproporphyrin excretion pattern. Where liver biopsy is performed for another indication, it shows the characteristic dark hepatic pigmentation.
• Rotor syndrome is generally distinguished by the specific pattern of results on a structured hepatobiliary imaging or excretion study, together with absence of the hepatic pigmentation characteristic of Dubin-Johnson syndrome.

• Gilbert syndrome requires no specific treatment. Management comprises reassurance about the entirely benign, clinically inconsequential nature of this common condition. Explain clearly that no dietary restriction, monitoring, or treatment is required, and that the condition has no relevant implication for long-term health or life expectancy.
• Crigler-Najjar syndrome type one requires intensive management given the substantial kernicterus risk. Phototherapy is used, though it becomes progressively less effective as the child grows and skin surface area relative to body mass declines.
• In Crigler-Najjar syndrome type one, phototherapy alone becomes inadequate to maintain safe bilirubin levels as the child matures. The great majority of affected individuals therefore eventually need liver transplantation, the only definitive, curative treatment.
• Crigler-Najjar syndrome type two is generally managed with phenobarbital, which induces residual enzyme activity. It produces a meaningful reduction in bilirubin levels in the great majority of affected individuals. This effective pharmacological option distinguishes management of the milder variant from the more severe type one.
• Dubin-Johnson syndrome and Rotor syndrome require no specific treatment. Management comprises reassurance about the benign nature of these conditions, as for Gilbert syndrome, given the absence of any associated hepatocellular dysfunction or long-term health consequence.
• Genetic counselling on the inheritance pattern and implications for family members underpins management across most of this group. Clear patient education distinguishes these benign, inherited conditions from acquired liver disease. Crigler-Najjar syndrome type one is the important exception, requiring intensive specialist management given its substantial associated risk.