A patient presents with very high levels of serum cholesterol. After a series of tests, it is concluded that the patient has high circulating levels of LDL cholesterol, but has normal levels of the hepatic LDL receptor. Which of the following could best explain the observations in this patient?
A) hepatocytes from the patient are defective in the selective removal of cholesterol from the LDL complex
B) hepatocytes from the patient have decreased levels of acyl-CoA:cholesterol acyltransferase ratio
C) the absence of the enzyme lipoprotein lipase in the endothelial cells of the liver
D) the patient has a mutated form of apoB-100
E) there is an altered level of phosphorylation of the LDL receptor

Question

Quizplus · Accepted Answer

A mutated form of apoB-100 can impair the binding of LDL to its receptor, leading to high circulating levels of LDL cholesterol despite normal levels of hepatic LDL receptors. LDL is taken up by cells via LDL receptor-mediated endocytosis. In order for LDL receptors to recognize and bind LDL, they require the presence of both apoB-100 and apoE (the LDL receptor is also called the apoB-100/apoE receptor). Therefore, in this patient with elevated serum LDL in the presence of normal levels of hepatic LDL receptors, the most likely possible cause is a defective apoB-100 protein associated with the circulating LDL.

A Patient Presents with Very High Levels of Serum Cholesterol