Lipid Biochemistry USMLE Step 1 Practice Question
A 3-year-old boy presents with failure to thrive, developmental delay, and progressive hepatosplenomegaly. Vital signs reveal HR 102/min, RR 24/min, temperature 37.2Ā°C. Laboratory studies show markedly elevated plasma cholestanol and cholestane-3Ī²,7Ī±,12Ī±-triol levels, with normal LDL cholesterol. Abdominal ultrasound demonstrates hepatic steatosis without cirrhosis. He denies diarrhea. Genetic testing confirms sterol 27-hydroxylase deficiency. Which pathologic process best explains his clinical presentation?
Answer choices
- ADefective oxysterol formation preventing initiation of bile acid synthesisCorrect answer
- BDecreased SREBP-2 activation impairing cholesterol synthesis upregulation
- CAccumulation of phospholipids due to blocked sphingomyelinase activity
- DInability to form lipoprotein particles in the endoplasmic reticulum
- EImpaired LDL receptor recycling leading to cellular cholesterol accumulation
- FNiemann-Pick type C (NPC1 mutation) causing lysosomal cholesterol trapping
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