1. From the Interdisciplinary Genetics Program (M.E.D., C.D.S.), Medical Scientist Training Program (M.E.D.), Department of Biostatistics (M.B.Z.), Department of Internal Medicine (K.R., C.D.S.), and Molecular Physiology and Biophysics (C.D.S.), Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City.