1. From the Neurogenetics Group, National Institute of Neurological Disorders and Stroke (G.G.L.), Bethesda, Md; Department of Neurology (J.F.M.), Mayo Clinic, Jacksonville, Fla; Baycrest Centre for Geriatric Care (D.T.S.), The Rotman Research Institute, University of Toronto, Ontario, Canada; London Health Sciences Center (V.H.), University of Western Ontario, London, Ontario, Canada.