1. From the Department of Medical Physiology (W.A.G., M.F., S.V., M.B.R., H.J.J.), University Medical Center, Utrecht, The Netherlands; the Experimental and Molecular Cardiology Group (C.R.B., J.P.P.S., A.A.M.W.) and the Department of Clinical Genetics (C.R.B., I.M.v.L., M.H.), Academic Medical Center, Amsterdam, The Netherlands; and the Department of Medical Statistics (L.S.), Leiden University Medical Center, Leiden, The Netherlands.