A patient with abdominal obesity, hypertriglyceridemia (TG 450 mg/dL), and low HDL is found to have reduced lipoprotein lipase (LPL) activity. LPL requires apolipoprotein C-II (apoC-II) as an activator. ApoC-II is carried primarily on HDL and transferred to chylomicrons and VLDL in the circulation. A patient with which genetic defect would have a phenotype indistinguishable from LPL deficiency?
- A ApoC-II deficiency ✓
- B ApoA-I deficiency
- C ApoE deficiency
- D ApoB-100 deficiency
Explanation
ApoC-II is an obligate activator of lipoprotein lipase (LPL). Without functional apoC-II, LPL cannot be properly activated even though the enzyme itself is structurally normal. The result is severe hypertriglyceridemia (Type I hyperlipoproteinemia phenotype) with chylomicronemia, eruptive xanthomas, recurrent pancreatitis, and lipemia retinalis — identical to primary LPL deficiency. ApoA-I is involved in LCAT activation and reverse cholesterol transport; its deficiency causes low HDL and premature atherosclerosis. ApoE deficiency impairs remnant clearance, causing Type III hyperlipidemia (beta-VLDL accumulation). ApoB-100 deficiency (hypobetalipoproteinemia) causes low LDL and VLDL levels.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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