TNF and inflammatory bowel disease: IBD cases with PP had a lower probability to be carriers of the HLA-Cw06 rs10484554 rare T allele (OR 0.2; 95% CI 0.1–0.7 p = 0.01) and a higher probability to be carriers of the TNF-α rs1799964 rare C allele (OR 3.0; 95% CI 1.2–7.5; p = 0.02), compared with psoriatic cases without paradoxical effect.