A 10-year-old boy with recurrent pancreatitis has triglycerides >10,000 mg/dL, eruptive xanthomas, and lipemia retinalis. Apolipoprotein C-II levels are undetectable. Lipoprotein lipase (LPL) activity measured in post-heparin plasma is absent after addition of normal plasma. This confirms deficiency of:

• A Lipoprotein lipase itself
• B Apolipoprotein E
• C Hepatic lipase
• D Apolipoprotein C-II (LPL cofactor) ✓

Explanation

Apo C-II is the obligatory cofactor that activates lipoprotein lipase at the endothelial surface. When normal plasma (containing Apo C-II) restores LPL activity in the post-heparin assay, the primary defect is Apo C-II deficiency rather than absent LPL protein. If LPL itself were absent, adding Apo C-II–containing normal plasma would not restore activity. Apo E deficiency causes type III hyperlipoproteinemia with elevated VLDL and chylomicrons but not isolated chylomicronemia at this level.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.