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11. - iced
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10-06-2006, 12:10 AM
A 38-year-old man in a rural area presents to a physician for an employment physical. Ocular examination reveals small opaque rings on the lower edge of the iris in the anterior chamber of the eye. Nodular lesions are found on his Achilles tendon. Successful therapy should be aimed at increasing which of the following gene products in hepatocyte cell membranes? A. Apo B-100 B. Apo B-100 receptor C. Apo E D. Apo E receptor E. Lecithin cholesterol acyltransferase
10-06-2006, 12:13 AM
iced, I have a question for you. Which chromosome is familial hypercholesterolemia associated with?
10-06-2006, 12:20 AM
The correct answer is B. This man has characteristic signs of familial hypercholesterolemia, an autosomal
dominant disorder affecting about 1 in 500 persons. The xanthomas on the Achilles tendon and the arcus lipoides (the opaque rings in the eye) are pathognomonic. Affected individuals have very high LDL cholesterol because of deficient endocytosis of LDL particles by LDL receptors. These receptors recognize the apo B-100 protein cotransported with cholesterol esters in LDL. Treatments aim at increasing genetic expression of LDL receptors (i.e., apo B-100 receptors) to enhance clearance of LDL particles. Dietary changes, a resin drug, niacin, or an HMG-CoA reductase inhibitor could be tried. Apo B-100 (choice A) is the apoprotein of liver-produced lipoproteins such as VLDL, IDL and LDL. It is therefore not in the hepatic cell membranes, and it might be expected to decrease with decreasing concentrations of circulating LDL. Apo E (choice C) is an apoprotein found on VLDL, IDL, and chylomicrons, allowing "scavenging" by the liver of remnants or of the lipoprotein itself. It is not found in the hepatocyte membrane. Apo E receptor (choice D) would actually be increased by the treatment with hypocholesterolemic agents. However, the apo E receptor is not involved in the scavenging of LDL particles. Lecithin cholesterol acyl transferase (choice E) or LCAT, is activated by apo AI, and esterifies free cholesterol in plasma. Plasma levels of HDL cholesterol and apo AI are inversely related to the risk of coronary heart disease. |
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