The study was renewed in FY 2001 through March, 2005. Further studies will be conducted in the cohort of 2,200 who had previously undergone overnight sleep studies. A total of 700 cohort members from families with sleep apnea, most of whom had a genome scan performed, will undergo additional physiological and biochemical measurements and longitudinal follow-up to derive detailed phenotypic characterization of sleep apnea and related cardiovascular disease risk factors and subclinical disease. Newly available technology will be used to quantify specific and sensitive indices of obstructive breathing parameters and sleep fragmentation. Subjects will also undergo a biochemical profile and evaluations of vascular functions, including assessment of novel cardiovascular disease risk factors that may be related to sleep apnea based on common genes or their role as indices of sleep apnea disease severity.