In the lipoprotein lipase (LPL) pathway, which apolipoprotein is essential for LPL activation, and what is the clinical consequence of its deficiency?

• A Apo C-II deficiency — impaired LPL activation, causing hyperchylomicronaemia (type I dyslipidaemia) with pancreatitis risk ✓
• B Apo B-48 deficiency — impaired chylomicron assembly
• C Apo E deficiency — impaired chylomicron remnant clearance, causing type III dyslipidaemia
• D Apo A-I deficiency — impaired reverse cholesterol transport and HDL formation

Explanation

Apo C-II is an obligate activator of lipoprotein lipase (LPL); it is transferred to chylomicrons and VLDL from HDL in the circulation. Without Apo C-II, LPL cannot hydrolyze triglycerides in chylomicrons and VLDL, causing massive hypertriglyceridaemia (Type I dyslipidaemia by Fredrickson classification). Triglyceride levels may exceed 1000 mg/dL, causing eruptive xanthomas, lipaemia retinalis, and severe acute pancreatitis. Treatment involves a very low-fat diet (<10–15 g/day). Apo E deficiency causes type III (dysbetalipoproteinaemia); Apo A-I is needed for LCAT activation and reverse cholesterol transport.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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