Question

A patient with multiple tendon xanthomas is found to have a serum cholesterol level of 398 mg/dL and an LDL level of 220 mg/dL. What is the most likely defect?

• A. Lipoprotein lipase deficiency
• B. LDL receptor defect
• C. Defective Apo B-100
• D. PCSK9 gain-of-function mutation

Hint:

In cases of familial hypercholesterolemia, look for tendon xanthomas and significantly elevated LDL levels. The defect usually lies in the LDL receptor.

Answer 1

The Correct Option is B

In biochemistry, multiple tendon xanthomas and elevated serum cholesterol and LDL levels are indicative of familial hypercholesterolemia. This condition is commonly caused by a defect in the LDL receptor. Let's break down why this is the most likely defect:

1. Lipoprotein lipase deficiency: This condition leads to hypertriglyceridemia, not hypercholesterolemia. It would result in elevated chylomicrons and VLDL rather than LDL.
2. LDL receptor defect: This is the most common cause of familial hypercholesterolemia. It results in elevated LDL levels because LDL particles can't be taken up by the liver effectively, hence the buildup in the bloodstream.
3. Defective Apo B-100: While this could also cause elevated LDL, it typically presents less severely than an LDL receptor defect and is less common.
4. PCSK9 gain-of-function mutation: This would increase LDL levels but is less common than an LDL receptor defect. Plus, the presence of tendon xanthomas strongly points toward familial hypercholesterolemia due to an LDL receptor defect.

Given these considerations, the LDL receptor defect is the most likely cause of the observed symptoms in this patient.