The classic view of psoriasis pathogenesis was established on the IL-12/Th1 pathway but has now been profoundly revised, and “under the IL-17 light”, the pathogenic role of IFN-γ has been reconsidered, placing it in the early steps of the psoriatic cascade, and acting as an activating factor for antigen-presenting cells. The gene discussed is IFNG; the disease is psoriasis.