Heme Metabolism MCQs

26 MCQs with clinical pearls · MBBS Biochemistry · Prof Jariya

Topics covered (5)

Jaundice — 9 MCQs
Heme Catabolism — 7 MCQs
Porphyrias — 6 MCQs
Heme Synthesis — 2 MCQs
2,3-BPG and Oxygen Transport — 2 MCQs

Sample MCQs with clinical pearls

A neonate with physiological jaundice receiving phototherapy is likely to have decreased activity of which of the following enzymes required for bilirubin clearance?

A) ALA synthase

B) Bilirubin UDP-glucuronosyl transferase ✔

C) Biliverdin reductase

D) Haem oxygenase

E) Porphobilinogen deaminase

PHOTOTHERAPY converts bilirubin → LUMIRUBIN (water-soluble structural isomer) and PHOTOBILIRUBIN → these can be excreted in bile and urine WITHOUT hepatic conjugation → BYPASSES the requirement for BILIRUBIN UDP-GLUCURONOSYL TRANSFERASE (UGT1A1). Therefore phototherapy effectively DECREASES THE NEED for UGT1A1 activity. This is why phototherapy works in Crigler-Najjar Type II (reduced but not absent UGT1A1) — phototherapy + residual UGT1A1 maintains acceptable bilirubin levels. 📹 [VIDEO LINK]

A 12-year-old boy presents with jaundice and bone pains after a hiking trip. His peripheral blood smear shows anaemia consistent with haemolysis. Bilirubin production in this boy is likely to be which of the following?

A) Equal to normal at 250mg per day

B) Greater than 100mg per day

C) Greater than 300mg per day ✔

D) Less than 100mg per day

E) Less than 300mg per day

NORMAL bilirubin production = ~250-300 mg/day. HAEMOLYTIC ANAEMIA → increased RBC destruction → bilirubin production GREATER THAN 300 mg/day → unconjugated hyperbilirubinaemia. Elevated urinary urobilinogen. No bilirubin in urine (unconjugated not water-soluble). Hiking trip = possible sickle cell crisis or G6PD-induced haemolysis. 📹 [VIDEO LINK]

A 24-year-old patient presents with acute abdominal pain and confusion. Urine analysis reveals elevated delta-aminolevulinic acid and porphobilinogen. Enzyme assay shows hydroxymethylbilane synthase deficiency. Which of the following is the likely diagnosis?

A) Acute intermittent porphyria ✔

B) Congenital erythropoietic porphyria

C) Erythropoietic protoporphyria

D) Porphyria cutanea tarda

E) Variegate porphyria

ACUTE INTERMITTENT PORPHYRIA (AIP): PBG DEAMINASE (hydroxymethylbilane synthase, HMBS) DEFICIENCY → ALA and PBG accumulate in urine (Watson-Schwartz test POSITIVE for PBG). Features: NEUROLOGICAL (abdominal pain, peripheral neuropathy, psychiatric symptoms, seizures), NO PHOTOSENSITIVITY. Triggers: barbiturates, OCP, fasting, alcohol. Treatment: HAEMATIN (suppresses ALA synthase), glucose loading, avoid triggers.\ \ 📹 [VIDEO LINK]

These are three of 26 MCQs in this section. Every question carries a clinical pearl explaining the reasoning.

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