ABCG2 and psoriatic arthritis: In addition, in the multivariate analysis a tendency was found towards association between patients carrying the ABCG2 rs13120400-T allele (T vs. CC: OR = 8.33; 95% CI = 1.24–164.79; p = 0.059) with psoriatic arthritis (OR = 5.60; 95% CI = 1.74–25.18; p = 0.009) and the risk of developing toxicity during treatment with MTX (all these values are shown in Table 3).