Lipid Biochemistry USMLE Step 1 Practice Question
A 48-year-old woman presents with progressive memory loss, peripheral neuropathy, and ataxia. Vital signs are stable (BP 118/76, HR 72, RR 14, Temp 37°C). MRI demonstrates cerebellar atrophy. Laboratory studies reveal severely depressed total cholesterol at 85 mg/dL, undetectable LDL cholesterol, and normal triglycerides at 110 mg/dL. Genetic testing identifies a SREBP-2 mutation. She denies statin use. Which mechanism best explains her neurological manifestations?
Answer choices
- AImpaired synthesis of apolipoprotein E in astrocytes
- BAccumulation of cholesterol-depleted HDL particles in the brain
- CDefective cholesterol homeostasis leading to inadequate myelin synthesis in the nervous systemCorrect answer
- DOxidative stress from absent antioxidants in low-density lipoproteins
- EEnhanced lipoprotein lipase activity degrading cerebral lipoproteins
- FDeficiency of 24S-hydroxycholesterol leading to impaired cholesterol efflux from the brain
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