Many polymorphisms in the TNFA, particularly in the promoter region, were reported to be related to PsA risk either dependent or independent of the HLA-C*06:02 [69,70] but with inconsistent functional results, i.e. the TNF-α mRNA and protein expression, in healthy people and disease groups including PsA [74–76] Nevertheless, the promoter polymorphisms of the TNFA are associated with autoimmune diseases including SLE and RA [76]. This evidence concerns the gene HLA-C and systemic lupus erythematosus.