Psoriasis: Association of interleukin-17 gene polymorphisms with severity and response to treatment.

Psoriasis is a chronic, inflammatory disease with a complex pathogenesis that is not yet fully understood. Although it is a multifactorial disease, the genetic factor has a major role in the pathogenesis of psoriasis. Genome wide association studies have identified over 50 genetic loci associated with psoriasis risk. Beside TNF-α or IL-23, the IL-17 family is a newer group that has proven implications in the pathogenesis of psoriasis. The most important members of the family, with pro-inflammatory qualities, are IL-17A and IL-17F. These interleukins are produced by a varied number of cells, but by far the most important are Th17 cells. Of the patients 20-30% present moderate-to-severe psoriasis, therefore, systemic medication (phototherapy, methotrexate, cyclosporine, acitretin or biologic agents) is mandatory. The necessity of an individualized treatment plan, for each patient, is imperative in order to establish the best strategy for non-responders to classical treatment or to other biologic treatments. The discovery of Th17 pathway improved the treatment and prognosis of psoriasis. Anti-psoriatic agents against IL-17 or its receptors are a novel group of biologic agents; these include ixekizumab, secukinumab and brodalumab. Polymorphisms of IL-17 family have been correlated with the severity and response to treatment in psoriasis, and also with the risk of inflammatory, infectious, autoimmune or neoplastic pathologies. The significant difference in the presence or absence of susceptibility loci in different population is due to genetic background and environmental factors that have a major impact on disease predisposition. In this study, we reviewed the importance and influence of the IL-17 polymorphisms as predictors of response to treatment and severity of the disease.