1. From Human Genetics Center (K.L.E.K., E.B., J.E.H.), University of Texas Health Science Center, Houston, Tex; Department of Human Genetics (C.F.S., T.J.R.), University of Michigan, Ann Arbor, Mich; Institute of Molecular Medicine (E.B., M.F.), University of Texas Health Science Center, Houston, Tex; Rockefeller University (S.C.H.), New York, NY; Department of Molecular Biology and Genetics (A.C.), Cornell University, Ithaca, NY.