Psoriasis (OMIM: 614204), a chronic inflammatory skin disorder, is characterized by the presence of red plaques anywhere in the body, excessive keratinocyte proliferation, and immune cell infiltration driven by dysregulated T helper 17 (Th17), which are defined by their production of Interleukin-17 (IL-17) in response to Interleukin-23 (IL-23) (2). The gene discussed is IL17A; the disease is psoriasis.