1 National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health Bethesda, MD Johns Hopkins University School of Medicine Baltimore, MD and Universitat Oberta de Catalunya, Barcelona, Spain.
2 National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health Bethesda, MD and Johns Hopkins University School of Medicine, Baltimore, MD.