Hyperchylomicronemia (type I) in childhood has been associated with which of the following?

Hyperchylomicronemia (type I) in childhood has been associated with which of the following?

• A. A deficiency of apo C-II
• B. A deficiency of LCAT
• C. A deficiency of LPL
• D. A deficiency of apo A-I

Answer: (A)

The key idea is that apo C-II is the essential activator of lipoprotein lipase (LPL), the enzyme that hydrolyzes triglycerides in chylomicrons. If apo C-II is deficient, LPL cannot effectively break down the triglycerides in chylomicrons after a meal, so chylomicrons accumulate in the blood. This leads to hyperchylomicronemia, the hallmark of type I hyperlipoproteinemia seen in childhood. While a lack of LPL itself can also cause a similar picture, the association highlighted here is specifically the deficiency of apo C-II as the activating cofactor for LPL. Defects in LCAT or apo A-I influence HDL metabolism rather than causing prominent chylomicron elevation, so they don’t fit the pattern of childhood hyperchylomicronemia driven by impaired chylomicron clearance.

The key idea is that apo C-II is the essential activator of lipoprotein lipase (LPL), the enzyme that hydrolyzes triglycerides in chylomicrons. If apo C-II is deficient, LPL cannot effectively break down the triglycerides in chylomicrons after a meal, so chylomicrons accumulate in the blood. This leads to hyperchylomicronemia, the hallmark of type I hyperlipoproteinemia seen in childhood. While a lack of LPL itself can also cause a similar picture, the association highlighted here is specifically the deficiency of apo C-II as the activating cofactor for LPL. Defects in LCAT or apo A-I influence HDL metabolism rather than causing prominent chylomicron elevation, so they don’t fit the pattern of childhood hyperchylomicronemia driven by impaired chylomicron clearance.