A 52-year-old man from Delhi presents with chest pain on exertion for 3 months. He has a 10-year history of type 2 diabetes mellitus (HbA1c 8.2%) and hypertension on amlodipine. Lipid profile shows: total cholesterol 285 mg/dL, LDL-C 180 mg/dL, HDL-C 32 mg/dL, triglycerides 320 mg/dL. Coronary angiography reveals 70% stenosis in the left anterior descending artery. He is started on atorvastatin 40 mg daily. After 6 weeks, repeat lipids show minimal improvement (LDL-C 165 mg/dL). Genetic testing reveals a heterozygous mutation in the LDL receptor gene. Which of the following best explains the poor response to statin therapy in this patient?

Explanation

## Familial Hypercholesterolaemia and Statin Resistance ### Pathophysiology of LDL Receptor Defects **Key Point:** Heterozygous familial hypercholesterolaemia (FH) results from mutations in the LDL receptor gene, causing defective or absent LDL receptors on hepatocytes. This impairs the clearance of LDL particles from circulation. **High-Yield:** Statins work by: 1. Inhibiting HMG-CoA reductase → decreased hepatic cholesterol synthesis 2. Upregulating LDL receptors on hepatocytes → increased LDL uptake In heterozygous FH, the mutant allele produces ~50% of normal LDL receptors. Even with statin-induced upregulation of the normal allele, total receptor number remains insufficient for adequate LDL clearance. ### Why This Patient Shows Poor Response **Clinical Pearl:** Heterozygous FH patients typically show 20–30% reduction in LDL-C with statins (vs. 40–50% in non-FH patients). This patient's minimal response (8% reduction) suggests: - Baseline LDL receptor deficiency limits compensatory upregulation - Reduced hepatic uptake of LDL particles → persistent elevation of circulating LDL - Genetic basis of resistance, not non-adherence or drug interaction ### Management Implications | Intervention | Mechanism | Expected LDL-C Reduction | | --- | --- | --- | | High-dose statin | Maximal HMG-CoA reductase inhibition + receptor upregulation | 20–30% in FH | | Ezetimibe addition | Blocks intestinal cholesterol absorption | Additional 15–20% | | PCSK9 inhibitor | Prevents LDL receptor degradation, increases surface receptors | 40–70% additional | | Inclisiran (PCSK9 siRNA) | Reduces PCSK9 synthesis | 40–50% additional | | Lipoprotein apheresis | Direct removal of LDL particles | 60–70% per session | **Mnemonic:** **FH-STATIN** = Familial Hypercholesterolaemia → Statins Are Therapeutic but INadequate (monotherapy) ### Why Other Options Are Wrong - **Option 1 (Increased HMG-CoA reductase activity):** Statins inhibit this enzyme; upregulation occurs but is offset by the genetic LDL receptor defect. - **Option 3 (Enhanced VLDL→LDL conversion):** Lipoprotein lipase activity is normal in FH; the primary defect is LDL clearance, not VLDL metabolism. - **Option 4 (Impaired apoB-100 synthesis):** ApoB-100 production is normal in FH; the defect is in the receptor, not the ligand. [cite:Harrison 21e Ch 393]