In particular, HLA-Cw6 is strongly associated with psoriasis and genome-wide association studies link psoriasis to polymorphisms of genes belonging to MHC class I pathway (ERAP1), IL-23 signaling pathway (IL12B, IL23A, and IL23R), cytokines pathways and Th17 polarization (STAT3), or NF-kB pathway (CARD14) (19). This evidence concerns the gene IL23A and psoriasis.