This is perhaps best exemplified by the IL‐23/IL‐17 axis, to which multiple autoimmune diseases have been linked, including psoriasis (SNPs in or near to IL23R, IL12B, TYK2 and STAT3), ankylosing spondylitis (SNPs in or near to IL23R, IL12B, TYK2 and JAK2) and multiple sclerosis (SNPs in or near to IL12B, IL12A, TYK2 and STAT3). The gene discussed is TYK2; the disease is psoriasis.