Lipid Biochemistry USMLE Step 1 Practice Question
A 35-year-old man with xanthomas on his Achilles tendons and corneal arcus presents with chest pain. Vital signs: BP 165/95 mmHg, HR 92/min, RR 16/min, Temp 37°C. Labs reveal LDL-cholesterol 450 mg/dL, HDL 28 mg/dL, triglycerides 180 mg/dL. Coronary angiography shows significant stenosis. DNA testing confirms a mutation in the LDL receptor gene preventing normal cell membrane translocation. No xanthoma eruptivum noted. Which intracellular consequence results from this mutation?
Answer choices
- AInability to internalize LDL particles, preventing suppression of HMG-CoA reductaseCorrect answer
- BDecreased synthesis of apolipoprotein B-100 due to SREBP-2 inactivation
- CImpaired esterification of intracellular cholesterol by ACAT
- DReduced activity of cholesterol 7α-hydroxylase in the endoplasmic reticulum
- EImpaired degradation of cholesterol to pregnenolone in mitochondria
- FAccumulation of VLDL remnants in the cytoplasm due to impaired apolipoprotein E receptor binding
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