1. Neurogenetics Laboratory, Massachusetts General Hospital, and Department of Genetics and Neuroscience Program, Harvard Medical School, Boston, MA 02114.
2. Imperial Cancer Research Fund, Lincoln's Inn Fields, London WC2A 3PX, England.
3. Department of Medical Genetics, Indiana University School of Medicine, Indianapolis, IN 46223.
4. European Molecular Biology Laboratory, D-69 Heidelbeg, Federal Republic of Germany.
5. Department of Neurology, Boston University School of Medicine, Boston, MA 02118.
6. Department of Biological Chemistry, California College of Medicine, University of California, Irvine, CA 92717.