NOD2 and psoriatic arthritis: An important contribution to this issue was provided by Zhu et al. that in 2012, in a meta-analysis of nine studies, confirmed the absence of association between psoriasis, psoriatic arthritis, and common polymorphisms of NOD2/CARD15; however the authors emphasized the importance of the protein encoded by this gene in the pathogenesis of psoriasis and psoriatic arthritis and the presence of conflicting results among the studies analyzed [26].