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Psoriasis is one of the multigenic and multifactorial diseases with an etiology that has yet to be thoroughly determined. Recent interventions with biologics and small-molecule inhibitors in the treatment of psoriasis have caused a drastic paradigm shift. Thanks to these novel therapeutic strategies, psoriasis research has progressed in turn. However, there is still a number of puzzles to be solved.

Despite accumulating knowledge of psoriasis genetics through the contribution of the genome project, it still remains controversial whether genome-wide association study (GWAS) is the best tool to identify the responsible gene. Because a number of recent studies have elucidated that psoriasis develops through altered innate and adaptive immunity, it is tempting to assume that psoriasis represents a cutaneous condition as a result of evolutional selection pressure over time so as to be resistant to microbial pathogens. Psoriasis is often comorbid and associated with obesity, diabetes and increased cardiovascular risk, namely metabolic syndrome. What are the molecular implications of these two conditions? Which is the cause and which the effect?

In this issue, we have four invited articles on psoriasis research regarding the genetics, immunological pathomechanism and their association with metabolic syndrome. Oka raises a problem in the analysis of psoriasis genes by GWAS, and is expecting a breakthrough by using the next-generation sequencing. Morizane et al. give an overview of the roles for antimicrobial peptides and innate immunity in the pathogenesis of psoriasis. Nakajima reviews a recent established theory, the interleukin-23/T-helper 17 axis, as the responsible adaptive immunity of psoriasis, as well as a psoriasis model mouse, K5.Stat3C transgenic. Finally, Takahashi highlights the association of psoriasis with metabolic syndrome in the context of adipocytokines and pro-inflammatory cytokines, which may be involved in the pathogenesis of both conditions.

We hope that these contributions help readers better understand the ongoing and future paradigm shift of psoriasis research.