LpX is associated with deficiency of which enzyme?

• A. LCAT
• B. CETP
• C. LPL
• D. HL

Answer: (A)

LpX forms when LCAT (lecithin cholesterol acyltransferase) activity is deficient. LCAT normally esterifies free cholesterol on HDL, transforming nascent HDL into mature, spherical HDL and enabling efficient reverse cholesterol transport. Without this esterification, free cholesterol and phospholipids accumulate and rearrange into an abnormal lamellar particle called lipoprotein X. This LpX is characteristic of LCAT deficiency (often seen in familial LCAT deficiency and related conditions).

Other enzymes listed have different roles in lipoprotein metabolism and do not produce LpX when deficient: CETP transfers cholesteryl esters between lipoproteins; LPL hydrolyzes triglycerides in chylomicrons and VLDL; HL remodels HDL and remnant particles. Their deficiencies do not lead to the formation of LpX.