1. From the Laboratory of Biochemical Genetics and Metabolism (H.M.D., S.A.C., J.L.S., J.L.B., J.D.S.) and Laboratory of Statistical Genetics (S.C.H.), Rockefeller University, and the Division of Hematology-Oncology (R.S.) and Division of Cardiology (L.F.L.), Department of Medicine, Cornell University Medical College, New York, NY; and Millennium Pharmaceuticals, Inc (P.S., K.J.M.), Cambridge, Mass.