OPRM1 and psoriasis: While effect allele ‘G’ of rs1799971 (OPRM1) also associated with increased risk of early onset and familial aggregation of psoriasis in the additive and dominant models (ORadditive = 1.75, 95% CI 1.27–2.43, p = 0.001, ORdominant = 1.82, 95% CI 1.26–2.63, p = 0.001).