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?