1. Department of Orthopaedic Surgery, Faculty of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
2. Third Department of Internal Medicine, Faculty of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
3. Laboratory of Molecular Genetics, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
4. Laboratory of Genetics, The Salk Institute for Biological Studies, La Jolla, California 92037