In a patient with lipoprotein lipase deficiency, which of the following is increased following a fatty meal?

Correct Answer: A. Chylomicron

Lipoprotein lipase (LPL) is the rate-limiting enzyme responsible for hydrolysis of triglycerides in chylomicrons and VLDL into free fatty acids and glycerol. In LPL deficiency (Type I hyperlipoproteinemia or familial chylomicronemia), this enzyme is absent or severely deficient. When a patient with LPL deficiency consumes a fatty meal, chylomicrons are synthesized normally in the intestinal epithelium and secreted into the lymph and blood. However, without functional LPL, these chylomicrons cannot be cleared from circulation—they accumulate massively in the bloodstream. This leads to severe hypertriglyceridemia (often >1000 mg/dL), with chylomicrons remaining in the blood for days instead of hours. The hallmark finding is milky or creamy appearance of blood plasma (lipemic plasma). The increased chylomicrons are the direct consequence of impaired catabolism, not increased synthesis. This is the pathognomonic response to a fatty meal in LPL deficiency and is the basis for the diagnostic fat-loading test used in Indian clinical practice.

Why the other options are wrong

B. Apo A — Apo A (apolipoprotein A-I) is a structural component of HDL and is involved in reverse cholesterol transport. In LPL deficiency, Apo A levels are typically normal or even low because HDL formation is not directly stimulated by a fatty meal. The defect is in triglyceride hydrolysis, not apolipoprotein synthesis. Apo A does not accumulate after a fatty meal in this condition. C. HDL — HDL (high-density lipoprotein) is not increased following a fatty meal in LPL deficiency. In fact, HDL may be reduced because LPL generates free fatty acids and glycerol that are normally used to remodel HDL particles. Without LPL activity, HDL formation and remodeling are impaired. A fatty meal does not trigger HDL synthesis; it triggers chylomicron secretion. D. LDL — LDL (low-density lipoprotein) is not acutely increased after a fatty meal in LPL deficiency. LDL is derived from VLDL remnants via hepatic lipase activity, a process that occurs over hours to days. A fatty meal directly stimulates chylomicron secretion, not LDL production. LDL levels may be secondarily affected but are not the primary acute response.

High-Yield Facts

Mnemonics

LPL Deficiency = Chylo ↑↑ Lipoprotein Lipase deficiency → Chylomicrons accumulate. No enzyme = no breakdown = accumulation. Use when you see 'fatty meal + LPL deficiency' → think chylomicrons, not HDL or LDL. Type I = Chylo Only Type I hyperlipoproteinemia = only chylomicrons elevated (not VLDL, not LDL). Distinguishes it from Type IIb (chylo + VLDL + LDL) and Type IV (VLDL only).

NBE Trap

NBE may lure students who confuse LPL deficiency with other dyslipidemias (e.g., Type IIb or familial hypercholesterolemia) where LDL or HDL changes are prominent. The trap is forgetting that LPL specifically hydrolyzes triglycerides in chylomicrons—not cholesterol or apolipoprotein synthesis.

Clinical Pearl

In Indian clinical practice, a patient presenting with recurrent acute pancreatitis and milky serum should raise suspicion for LPL deficiency. A simple fat-loading test (50 g fat meal) showing persistent chylomicronemia confirms the diagnosis and guides dietary fat restriction to prevent life-threatening pancreatitis—a common presentation in Indian pediatric and adult populations.

_Reference: KD Tripathi Pharmacology Ch. 32 (Lipid-Lowering Drugs); Robbins Pathology Ch. 5 (Disorders of Lipid Metabolism); Harrison Principles of Internal Medicine Ch. 356 (Lipid Disorders)_