1. Department of Neurology, Clinical Research Institute, Seoul National University Hospital, Seoul 110-744, South Korea.
2. Medical Research Center, Seoul National University, Seoul 110-744, South Korea.
3. Medical Research Institute, Chungang University College of Medicine, Seoul 156-756, South Korea.
4. Division of Neurology, Department of Medicine, University of British Columbia, Vancouver, BC V6T 2B5, Canada.