Lipid Biochemistry USMLE Step 1 Practice Question
A 6-year-old boy with failure to thrive and chronic steatorrhea presents with BP 95/60, HR 98, RR 22, temp 37°C, SpO2 98%. He reports fat-soluble vitamin deficiencies (A, D, E, K) causing night blindness and bone pain. Laboratory studies reveal elevated serum cholesterol (320 mg/dL) and triglycerides (480 mg/dL) despite severe fat malabsorption. Plasma apolipoprotein B is undetectable. PT/INR is prolonged. Which genetic mutation best explains this paradoxical lipid profile?
Answer choices
- AMicrosomal triglyceride transfer protein (MTP) deficiency preventing chylomicron and VLDL assemblyCorrect answer
- BPrimary defect in long-chain fatty acid oxidation causing lipid accumulation in intestine
- CLipoprotein lipase deficiency with severe hypertriglyceridemia and chylomicron accumulation
- DAbetalipoproteinemia secondary to pancreatic insufficiency and fat malabsorption
- EMutations in apolipoprotein B gene preventing normal protein synthesis
- FMutations in apolipoprotein C-II gene impairing lipoprotein lipase cofactor activity
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