Lipid Biochemistry USMLE Step 1 Practice Question
A 55-year-old man with familial hypercholesterolemia presents with persistent elevation of LDL cholesterol at 320 mg/dL despite maximal atorvastatin and ezetimibe therapy. Vital signs are stable (BP 138/82, HR 78). Laboratory studies show normal AST/ALT and CK levels; fasting lipid panel confirms LDL 320 mg/dL. He has no muscle pain or weakness. A PCSK9 inhibitor is initiated. Which mechanism best explains LDL cholesterol reduction by PCSK9 inhibition?
Answer choices
- APrevention of PCSK9-mediated lysosomal degradation of LDL receptors, increasing hepatic LDL uptakeCorrect answer
- BDirect inhibition of HMG-CoA reductase in hepatocytes
- CStimulation of LDL receptor expression through SREBP-2 activation
- DInhibition of apoB-100 synthesis in the liver
- EEnhanced triglyceride hydrolysis by lipoprotein lipase in peripheral tissues
- FIncreased conversion of VLDL to LDL through enhanced hepatic triglyceride metabolism
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