A 40-year-old man with a 10-year history of type 1 diabetes mellitus comes to the physician for a routine examination. He was diagnosed with pancreatitis 25 years ago after a 2-year history of recurrent abdominal pain. Physical examination shows a thin habitus and abdominal tenderness. After a 12-hour fast, his serum triglyceride concentration is 4000 mg/dL (normal = 60-134). Intravenous heparin is administered in order to examine the patient's lipoprotein lipase activity. Plasma lipoprotein lipase activity is assayed and is extremely deficient in this man's blood. Which of the following proteins is most likely deficient in this patient?

Question

Quizplus · Accepted Answer

ApoC-II is a cofactor for lipoprotein lipase, which is necessary for the hydrolysis of triglycerides in chylomicrons and VLDL. A deficiency in apoC-II leads to hypertriglyceridemia due to impaired lipoprotein lipase activity.  ApoC-II is present in chylomicrons, LDL, and HDL and is required for the activation of the endothelial cell-associated triglyceride lipase called lipoprotein lipase (LPL). Loss, or defective activity, of apoC-II would result in circulating lipoproteins of all types enriched in triglyceride, leading to hypertriglyceridemia. Additional symptoms associated with apoCII deficiency include eruptive xanthomas, pancreatitis, and hepatosplenomegaly. The hepatosplenomegaly is the cause of the abdominal tenderness.

A 40-Year-Old Man with a 10-Year History of Type 1