1. From the Division of Epidemiology and Clinical Applications (T.A.M., C.J.O.), National Heart, Lung, and Blood Institute, Bethesda, Md; the Human Genetics Center (E.B.), University of Texas Health Science Center at Houston, Houston, Tex; the National Heart, Lung, and Blood Institute Framingham Heart Study (C.J.O.), Framingham, Mass; and the Inherited Disease Research Branch (A.F.W.), National Human Genome Research Institute, Baltimore, Md.