Lipid Biochemistry USMLE Step 1 Practice Question
A 3-year-old boy presents with failure to thrive and steatorrhea since infancy. Vital signs show HR 110, RR 22, normal BP and temperature. Laboratory studies reveal markedly elevated triglycerides (1,200 mg/dL), low HDL (18 mg/dL), and impaired chylomicron clearance on lipoprotein electrophoresis. Fat-soluble vitamin levels are reduced. Abdominal examination reveals hepatosplenomegaly without tenderness. A genetic defect in lipoprotein lipase is suspected. Which mechanism best explains his gastrointestinal symptoms?
Answer choices
- ADefective uptake of chylomicron remnants by hepatocytes
- BIncreased fecal loss of bile acids
- CInability to digest dietary triglycerides into fatty acids and glycerolCorrect answer
- DReduced activity of pancreatic lipase in the small intestine
- EImpaired synthesis of apolipoprotein B-48 in intestinal epithelial cells
- FDecreased absorption of long-chain fatty acids due to reduced micelle formation
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