Psoriatic arthritis

Psoriatic arthritis (PsA) is a complex genetic disorder that results from an interplay between multiple genetic and environmental factors. Although the exact pathogenesis of PsA is unclear, there is a substantial contribution of genetic factors to the etiology of PsA [1].Cumulative evidence not only implicates genetic determinants for disease susceptibility, but they are also important for disease expression [2, 3]. Evidence for the genetic basis of PsA is based on data gathered from family based investigations, population based studies, association studies with HLA antigens, genome wide linkage scans, and positional candidate gene studies within and outside the major histocompatibility (MHC) region. The marked increase in the prevalence of psoriasis in first degree relatives of probands with PsA [4], along with the immunological overlaps between these two diseases [5], is highly suggestive of shared genetic factors between psoriasis and PsA. Thus, supporting evidence for the genetic burden of PsA also comes from studies in the genetics of psoriasis, especially since the latter disease has been studied more extensively [5]. The greater emphasis on the genetics of psoriasis is in part due to a higher prevalence of psoriasis,which facilitates the recruitment of affected sibling pairs for genome wide linkage analysis. As PsA occurs in approximately one in three to five subjects with psoriasis, the occurrence of affected sibling pairs in PsA is approximately 25-fold less prevalent. © Springer-Verlag Berlin Heidelberg 2005.