Mutations in IL36RN/IL1F5 are associated with the severe episodic inflammatory skin disease known as generalized pustular psoriasis

Abstract

Generalized pustular psoriasis (GPP) is a rare and yet potentially lethal clinical variant of psoriasis, characterized by the formation of sterile cutaneous pustules, neutrophilia, fever and features of systemic inflammation. We sequenced the exomes of five unrelated individuals diagnosed with GPP. Nonsynonymous, splice-site, insertion, and deletion variants with an estimated population frequency of <0.01 were considered as candidate pathogenic mutations. A homozygous c.338C>T (p.Ser113Leu) missense substitution of IL36RN was identified in two individuals, with a third subject found to be a compound heterozygote for c.338C>T (p.Ser113Leu) and a c.142C>T (p.Arg48Trp) missense substitution. IL36RN (previously known as IL1F5) encodes an IL-1 family receptor antagonist, which opposes the activity of the IL-36A and IL-36G innate cytokines. Homology searches revealed that GPP mutations alter evolutionarily conserved residues. Homozygosity for the c.338C>T (p.Ser113Leu) variant is associated with an elevated proinflammatory response following ex vivo stimulation with IL36A. These findings suggest loss of function of IL36RN as the genetic basis of GPP and implicate innate immune dysregulation in this severe episodic inflammatory disease, thereby highlighting IL-1 signaling as a potential target for therapeutic intervention.

Figure 1

Clinical Features of Generalized Pustular Psoriasis (A) Individual GPP-02 II:1. Note extensive plaques of erythema with superimposed pustules on the arm. (B) Individual GPP-01 II:5. Note erythematous, intensely inflamed skin with active pustulation and desquamation on the buttocks. (C) Individual GPP-03 II:2. Note widespread, healing erythematous plaques following active pustulation on the legs.

Figure 2

Mutation and Segregation Analysis (A) Pedigrees and mutation status of three GPP kindreds in whom mutations were identified in IL36RN. (B) Sequence chromatograms of the c.338C>T (p.Ser113Leu) and c.142C>T (p.Arg48Trp) mutations.

Figure 3

Location of the Two Identified Mutations (A) Location of the two identified mutations with respect to the genomic organization of IL36RN (upper panel) and IL36RN (lower panel). (B) Locations of the c.142C>T (p.Arg48Trp) and c.338C>T (p.Ser113Leu) mutations with respect to the three-dimensional structure of IL36RN, including the loop domains and critical residues that mediate receptor interaction.

Figure 4

Analysis of Case and Control PBMCs, after Ex Vivo Stimulation with IL-36A (A) The induction of IL1A, IL6, and IL8 mRNA was assessed by real-time PCR, with the RPLPO transcript used as an endogenous control. Data are plotted as the mean, and error bars represent the SEM of duplicate stimulations with the expression level of the unstimulated sample set as a baseline value. CTR, control. (B) The concentration of IL-1α, IL-6, IL-8, and TNF was assayed in the PBMC culture medium. Data are plotted as the mean, and error bars represent the SEM of duplicate stimulations. All significance values were calculated via a one-way ANOVA test, followed by a Bonferroni posttest. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001. CTR, control.