AP1S3 and palmoplantar pustulosis: Of note, IL36RN, CARD14, and AP1S3 mutations have also been described in patients with PPP and those with ACH, demonstrating a shared genetic basis for pustular forms of psoriasis.5, 7, 8 Patients harboring disease alleles at 2 distinct loci (IL36RN and AP1S3; IL36RN and CARD14) have also been reported.9, 10 Thus an increasingly complex picture is emerging with evidence of substantial genetic heterogeneity, pleiotropy (the phenomenon whereby a single gene can influence more than 1 trait), and digenic inheritance.