[1] NIA, Neurogenet Lab, Bethesda, MD 20892 USA
[2] UCL Natl Hosp Neurol & Neurosurg, Reta Lila Weston Inst Neurol Studies, London, England
[3] Univ Minnesota, Dept Biochem, Dept Lab Med & Pathol, Minneapolis, MN USA
[4] Univ Minnesota, Inst Human Genet, Minneapolis, MN 55455 USA