A 25-year-old man requests cholesterol screening because of a family history of premature coronary artery disease (CAD). His lipid levels reveal an elevated total and LDL cholesterol. The high-density lipoprotein (HDL) and triglyceride values are normal. His physical examination is completely normal. Which of the following is the most common cause of genetic dyslipidemia?: (A) familial combined hyperlipidemia, (B) familial hypercholesterolemia, (C) familial defective Apo B, (D) Apo C-II deficiency
Answer is A. Familial combined hyperlipidemia has an incidence of 1/100. It is an autosomal dominant disorder and different affected family members may display different dyslipidemic phenotypes. Familial hypercholesterolemia (1/500) and familial defective Apo B (1/1000) are also common. The other two disorders (Apo C-II deficiency and lipoprotein lipase deficiency) are extremely rare.