Low levels of 5-HT increase the production of some inflammatory mediators, such as TNF-α and IL-1β, which induces the activation and deterioration of keratinocytes via NF-kB, which is activated by IL-17A in the prefrontal cortex and in the hippocampus, thus worsening the symptoms of psoriasis [165,166]. The gene discussed is IL17A; the disease is psoriasis.