Recent genome-wide association studies (GWAS) have identified single-nucleotide polymorphisms (SNPs) near HLA-C, tumor necrosis factor (TNF) receptor superfamily member 9 (TNFRSF9), and late cornified envelope 3A (LCE3A) as being more strongly associated with psoriasis than PsA, whereas SNPs near interleukin 23 receptor (IL-23R) and TNF alpha-induced protein 3 (TNFAIP3) were more strongly associated with PsA than with PsC32. The gene discussed is TNFRSF9; the disease is psoriasis.