In this study, all patients with PsA fulfilled the CASPAR criteria for the diagnosis, and we decided not to classify PsA according to phenotypes for two reasons: (i) the phenotypes of PsA have been shown to change over time [22]; (ii) the enrolled PsA patients, consisting of the distal subtype, the oligoarticular subtype, the polyarticular subtype, and the spondylitis subtype, all showed the similar high expression level of SIRT2 in PBMCs. Here, SIRT2 is linked to spondylitis.