In this retrospective study, we analyzed data from a total of 52 patients with moderate-to-severe psoriasis treated with guselkumab in daily clinical practice up to 1 year who either had not responded, or had contraindications or were intolerant to traditional systemic therapies or who had not responded to anti-TNFα, anti-IL-17, or anti-IL-12/IL-23 biological drugs. The gene discussed is IL17A; the disease is psoriasis.