A 22-year-old Indian medical student presents with recurrent episodes of mild jaundice triggered by examination stress and fasting. Liver function tests show unconjugated hyperbilirubinemia (total bilirubin 3.2 mg/dL, direct bilirubin 0.3 mg/dL), with normal transaminases and alkaline phosphatase. Genetic testing reveals a TA repeat polymorphism in the promoter region affecting the enzyme marked **C** in the heme degradation pathway diagram. Which of the following best describes the functional consequence of this genetic variant and its clinical management?

Explanation

## Why option 1 is correct The TA repeat polymorphism in the UGT1A1 promoter region (marked **C** in the diagram) causes reduced, not absent, enzyme expression. This results in Gilbert syndrome—a mild, benign unconjugated hyperbilirubinemia affecting 5–10% of the Indian population. The clinical presentation (stress-triggered jaundice, normal LFTs except unconjugated bilirubin, autosomal recessive inheritance) is pathognomonic. Gilbert syndrome requires no pharmacological treatment; management is reassurance and avoidance of precipitants (fasting, stress, illness). This directly aligns with Harper 32e and Robbins 10e, which classify Gilbert's as a benign condition with excellent prognosis. ## Why each distractor is wrong - **Option 2**: Describes Crigler-Najjar type I (complete UGT1A1 absence), which presents with severe neonatal jaundice and kernicterus risk. This patient is 22 years old with mild, intermittent jaundice—incompatible with type I. Type I would have presented with life-threatening hyperbilirubinemia in the neonatal period. - **Option 3**: Describes Crigler-Najjar type II (partial UGT1A1 deficiency), which does respond to phenobarbital. However, the TA repeat polymorphism is diagnostic of Gilbert syndrome, not type II. Type II is a rare autosomal recessive condition caused by different mutations; Gilbert's does not respond to phenobarbital induction. - **Option 4**: Implicates biliverdin reductase (marked **B**), not UGT1A1 (**C**). The genetic variant is in the UGT1A1 promoter, not in the biliverdin reductase gene. Phototherapy and exchange transfusion are not indicated in Gilbert syndrome. **High-Yield:** Gilbert syndrome = mild UGT1A1 deficiency (TA repeat) → benign unconjugated hyperbilirubinemia triggered by stress/fasting; reassurance only. Crigler-Najjar type I = complete absence → neonatal kernicterus. Type II = partial → phenobarbital responsive. [cite: Harper 32e Ch 31; Robbins 10e Ch 18]