PRTN3 and ankylosing spondylitis: 25(OH)D 25-hydroxyvitamin D, OR odds ratio, BMI body mass index, HAQ (0–3): health assessment questionnaire, ACPA anti-cyclic citrullinated peptide antibodies, HLA-B27 histocompatibility antigen HLA-B27, BASFI (0–10) Bath ankylosing spondylitis functional index