Which abnormal lipoprotein is described as sinking prebetalipoprotein?

• A. B-VLDL
• B. Lp(a)
• C. IDL
• D. LpX

Answer: (B)

The concept tested is how abnormal lipoproteins behave on electrophoresis and what their migration patterns indicate. Pre-beta lipoproteins correspond mainly to VLDL, which migrates ahead of the beta region during separation. An abnormal lipoprotein described as a sinking prebetalipoprotein has mobility in that pre-beta area. Lipoprotein(a) fits this description because it is an LDL-like particle that carries an additional apolipoprotein(a); this apo(a) component alters its electrophoretic behavior so it behaves like a pre-beta particle, giving it the sinking prebeta pattern. The other options have different migration patterns: beta-VLDL tends to run with the beta region, IDL occupies a transitional position, and LpX shows a distinct pattern associated with cholestasis, not the pre-beta/sinking pattern described here.