Too Much of a Good Thing

Psoriasis is a polygenic disorder characterized by a cutaneous environment highly enriched in antibacterial peptides, many of which appear to signal similarly to cytokines. Investigators from the Netherlands, Germany, and the U.K. investigated variations in the gene copy number of a gene cluster encoding one class of such peptides, called β-defensins, as a possible genetic risk factor for psoriasis.

The β-defensin gene cluster consists of eight genes located on the short arm of human chromosome 8. Seven of these genes (all but DEFB1) are located on a repeating unit that can appear one to six times per haploid genome (2 to 12 copies per cell). Using several different methods, the researchers determined the number of copies of the defensin rep…