Genetic variation and psoriasis

Abstract

Psoriasis is a common chronic inflammatory skin disease with a strong genetic basis, characterized by complex alteration in epidermal growth and differentiation. The genetic basis of psoriasis has been appreciated for nearly 100 years, but only recently have several of the genetic variants involved in psoriasis pathogenesis been identified. These genetic variants so far identified are the HLA-Cw*0602 allele of the HLA-C gene on chromosome 6, the p40 subunit of the IL-12 and IL-23 cytokines (IL12B), the IL-23 receptor and SNF313, a gene implicated in protein ubiquitinylation. Psoriasis patients have also been shown to have an increased number of copies of the beta-defensin gene cluster on chromosome 8. Beta-defensin 2, which is located in this region, is amongst the most highly up-regulated proteins in lesional skin and has cytokine-like properties in addition to potent antimicrobial activity. Although several additional genes remain to be identified, the variants that have so far been described support the autoimmune basis of psoriasis indicating that the disease may be mediated by T-cells reacting against (self)antigen(s) in the binding pocket of HLA-C, with contribution from the recently described Th17 subset of T-cells which are maintained by the IL-23 cytokine axis. These genetic variants together with pro-inflammatory environment caused by exaggerated antimicrobial response (beta-defensins) and dysregulation of signaling pathways (ubiquination), suggest the type of mechanism by which psoriasis can arise. Elucidation of the genetic basis of psoriasis and the underlying pathogenic mechanisms hold the potential for eventual cure of this enigmatic disorder.