title: Reply.
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD.|Columbia University Medical Center, New York, NY.
authors.forename: Runsheng
authors.initials: R
authors.lastname: Wang
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Ward
mesh_terms: D018450:Disease Progression; D006801:Humans; D025241:Spondylarthritis; D013167:Spondylitis, Ankylosing