Apolipoprotein A-I Gene Polymorphism and Atherosclerosis

BACKGROUND: Apolipoprotein (apo) A-I is the major protein constituent of plasma high density lipoproteins (HDL). HDL has been shown to promote cholesterol efflux from cells in vitro. Decreased plasma concentrations of HDL cholesterol and Apo A-I have been associated with premature coronary artery disease due to atherosclerosis in our society. A genetic HDL deficiency, familial hypoalphalipoproteinemia, appears to be fairly common in patients with premature coronary artery disease. The gene for Apo A-I has been isolated and characterized. Preliminary studies indicate that a specific Apo A-I gene polymorphism, detected following Pst I restriction enzyme digestion utilizing a specific probe, is significantly more common in subjects with premature coronary artery disease than in normal control subjects, and in some kindreds is associated with genetic HDL deficiency. This Apo A-I gene polymorphism is due to an alteration in the Apo A-I, Apo C-III intergenic region, near the 3' end of the coding region for Apo A-I. These observations have important implications for the detection of individuals genetically predisposed to premature coronary disease, as well as for providing insights into the mechanism leading to atherosclerosis. DESIGN NARRATIVE: Questionnaires were used to obtain information from each patient on known risk factors and diet. Fasting blood samples were obtained for lipoprotein analysis. Standard clinical and cardiological information and fasting blood samples were also collected for the cases. Blood was drawn for the DNA studies. A determination was made as to whether the Pst I Apo A-I gene polymorphism was associated with diminished levels of plasma Apo A-I or HDL cholesterol, by analysis of the distribution of these variables in cases and controls, after controlling for other known risk factors. Linkage analysis was used to determine whether the Pst I Apo A-I gene polymorphism co-segregates with premature coronary disease, or with diminished levels of plasma Apo A-I, or HDL cholesterol in 50 kindreds. A characterization was made of the abnormality in the Apo A-I, Apo C-III, Apo A-IV gene complex in patients with HDL deficiency, premature coronary disease, and the Pst I Apo A-I gene polymorphism.