GC and ankylosing spondylitis: Abbreviations: AU = anterior uveitis; AAU = acute anterior uveitis; AS = ankylosing spondylitis; ASAS = Assessment of SpondyloArthritis Society; DBP = vitamin D binding protein; ESSG = European Spondyloarthropathy Study Group; HLA-B27 = human leukocyte antigen B27; IBD = inflammatory bowel disease; PsA = psoriatic arthritis; ReA = reactive arthritis; SpA = spondyloarthritis; TLRs = Toll-like receptors; TNFα = tumor necrosis factor α; unSpA = undifferentiated spondyloarthritis