Psoriasis and Down syndrome: a report of three cases and a potential pathophysiologic link.

Psoriasis is thought to result from an influx of Th1 and Th17 cells driven by the production of cytokines such as interferon (IFN)-gamma, IL-2, and tumor necrosis factor (TNF)-alpha elicited by skin immunocytes. We report three cases of patients with chronic plaque psoriasis and concomitant Down syndrome. Although there is no direct link between Down syndrome and the Th17 pathway, there are data supporting a dysregulation of the IFN system in this patient population. The percentage of Th1 lineage cells (IFN-gamma producing CD4+ and CD8+ T cells) is substantially higher in patients with Down syndrome and serum levels of IFN-gamma in patients with Down syndrome are significantly elevated when compared to healthy controls. We propose that people with Down syndrome have a greater prevalence of psoriasis secondary to both high serum levels of and an enhanced sensitivity to IFN-gamma.