Using case/control and family designs, the study: 1) extends the finding that apolipoprotein E epsilon4 (APOE e4) increases the risk of sleep apnea in the general population; 2) examines if polymorphisms in other genes regulating lipid levels are associated with sleep apnea; 3) studies the relationship between lipid regulatory gene polymorphisms, lipid profile (LDL- cholesterol, HDL-cholesterol, triglycerides), plasma leptin (and other lipid regulatory hormones), and sleep apnea levels.