Examples of established systemic therapies for moderate-to-severe psoriasis include methotrexate, anti-tumor necrosis factor (TNF) agents (e.g., adalimumab, infliximab, etanercept, and certolizumab), anti-IL-12/23 antibody ustekinumab and anti-IL-23 antibodies (e.g., guselkumab, risankizumab and tildrakizumab), anti-IL-17A antibodies (e.g., secukinumab and ixekizumab), and anti-IL-17RA antibody brodalumab. This evidence concerns the gene IL17A and psoriasis.