Lipid Biochemistry USMLE Step 1 Practice Question
A 42-year-old woman presents with progressive jaundice and hepatosplenomegaly (liver 4 cm below costal margin). She reports ataxia and vertical supranuclear gaze palsy. Vital signs: BP 118/76, HR 88, RR 16, Temp 37°C, SpO2 98%. Laboratory analysis reveals elevated serum cholestanol and unesterified cholesterol levels. Bone marrow examination shows sea-blue histiocytes. Genetic testing confirms NPC1 mutations. She denies recent alcohol use. Which mechanism best explains the pathophysiology of her condition?
Answer choices
- AIncreased LDL receptor-mediated cholesterol uptake with defective SREBP-2 feedback
- BAccumulation of oxidized cholesterol esters in macrophages
- CBlockade of hepatic bile acid synthesis secondary to cholestasis
- DImpaired intracellular cholesterol trafficking from late endosomes/lysosomes to the endoplasmic reticulumCorrect answer
- EDefective cholesterol synthesis leading to decreased cell membrane integrity
- FGaucher disease (acid beta-glucosidase deficiency)
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