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A 38-year-old man is brought to the emergency department with crushing chest pain radiating to his left arm and mild shortness of breath that began approximately 30 minutes ago. ECG showed ST-segment elevation in leads II, III, AVF, and V4-V6 and a threefold increase in cardiac enzyme levels. His medical history is negative, but he has a positive family history of “heart problems” in his brother and in several members on his father’s side of the family. Physical examination reveals numerous painless yellow bumps on his elbows, knees, and ankle, which he has had since late childhood. His blood triglyceride level is 130 mg/dL, and his LDL cholesterol level is 320 mg/dL. The remaining laboratory values are unremarkable. Which of the following is the most likely explanation for these findings?
A. Excessive alcohol consumption
B. Inheritance of one mutant LDL cholesterol receptor gene
C. Lack of thyroid hormones
D. Lipoprotein lipase abnormality
E. Resistance to insulin hormone





The correct answer is B. Familial hypercholesterolemia is caused by an absent or defective cell surface receptor for LDL cholesterol molecules. The heterozygous form of this autosomal codominant disorder is associated with elevated LDL cholesterol levels (200-400 mg/dL); normal triglyceride levels; coronary heart disease (CHD) in the 30s-40s; corneal arcus; skin xanthomas on the elbows, knees, and especially the Achilles tendons; and a positive family history of hypercholesterolemia and CHD. The homozygous form is very rare and presents as high levels of LDL cholesterol (>500 mg/dL), symptomatic CHD before puberty, and sudden death usually before age 30 years. Numerous other genetic abnormalities can produce a similar lipid profile and early onset CHD, but they are very rare compared with familial hypercholesterolemia.

Answer A is not correct. Chronic alcohol consumption can cause elevated triglyceride and HDL cholesterol levels. High triglyceride levels typically decline after decreasing alcohol use. This patient has a typical presentation for a genetic disorder of lipid metabolism, with a strong family history, but a secondary cause of hyperlipidemia should always be considered before starting lipid-lowering treatment.

Answer C is not correct. Hypothyroidism is one of the secondary causes of hyperlipidemia. There are no signs of hypothyroidism in either the patient’s history or the physical examination, but any patient who presents with hyperlipidemia should be screened for hypothyroidism.

Answer D is not correct. Familial hyperchylomicronemia is a rare autosomal recessive genetic abnormality of enzyme lipoprotein lipase that is associated with elevated fasting triglyceride levels (>1000 mg/dL), moderately high LDL cholesterol levels, recurrent episodes of pancreatitis during childhood, lipemia retinalis (creamy white retinal vessels), eruptive xanthomas, and hepatosplenomegaly. CHD is not a common feature of this disease. This patient’s clinical presentation and lipid profile are not consistent with this diagnosis.

Answer E is not correct. Resistance to insulin is one of the underlying mechanisms causing type 2 diabetes mellitus (DM). In obese patients with uncontrolled type 2 DM, a diabetic dyslipidemia may be seen, which includes elevated levels of triglycerides and total cholesterol and decreased levels of HDL cholesterol. Treatment of choice is exercise, diet, and hypoglycemic therapy. In patients with controlled type 1 DM, the lipid profile is usually normal or possibly the LDL cholesterol level is slightly increased.
 
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