As shown in Fig. 3k, the combination of low IHC score for CD117+ (IHC score = 1) and high IHC score for CD138+ cells (IHC score = 3) significantly differentiates PsA than Abneg RA synovitis [OR (95% CI), 34.04 (1.535–2.398); p = 0.0002]. The gene discussed is SDC1; the disease is rheumatoid arthritis.