PDCD1 and ankylosing spondylitis: Studies on PDCD1 polymorphisms have demonstrated its association with several autoimmune diseases including systemic lupus erythematosus (SLE) [13-17], rheumatoid arthritis (RA) [18], type I diabetes (TID) [19], multiple sclerosis (MS) [20], ankylosing spondylitis (AS) [21], and Graves' disease [22],  although there are also some conflicting results [23-27].