TNF and ankylosing spondylitis: Although many studies have investigated the relationship between promoter region SNPs in the TNFα gene and the susceptibility to rheumatoid arthritis (RA), ankylosing spondylitis (AS), Crohn’s disease, PsV, and PsA [9]–[13], the association between TNFα promoter SNPs and PsV & PsA risk have produced inconsistent results.