AP1S3 and palmoplantar pustulosis: In pustular forms, mutations and polymorphisms have been described in the genes CARD14, AP1S3, and IL36RN [9,10,11], although the proportion of subjects harboring IL36RN-mutated alleles seems to be higher in generalized pustular psoriasis (GPP) than in palmoplantar pustulosis (PPP), the prevalence of AP1S3 mutations seems to be similar across these disease types and CARD14 mutations are observed in only a small minority of cases [11,12,13].