Generalized pustular psoriasis (GPP) is a rare inflammatory skin disease that can be life-threatening. Recently, it has been reported that familial GPP is caused by homozygous or compound heterozygous mutations of IL36RN. However, the majority of GPP cases are sporadic and it is controversial whether IL36RN mutations are a causative/predisposing factor for sporadic GPP. We searched for IL36RN mutations in two groups of GPP patients in the Japanese population in this study: GPP without psoriasis vulgaris (PV), and GPP with PV. Eleven cases of GPP without PV (GPP alone) and 20 cases of GPP accompanied by PV (GPP with PV) were analyzed. Surprisingly, 9 out of 11 cases of GPP alone had homozygous or compound heterozygous mutations in IL36RN. In contrast, only 2 of 20 cases of GPP with PV had compound heterozygous mutations in IL36RN. The two cases of GPP with PV who had compound heterozygous mutations in IL36RN are siblings, and both cases had PV-susceptible HLA-A*0206. We determined that GPP alone is a distinct subtype of GPP and is etiologically distinguished from GPP with PV, and that the majority of GPP alone is caused by deficiency of the interleukin-36 receptor antagonist due to IL36RN mutations.

The skin surface is colonized by a wide variety of fungi and bacteria. While many of these organisms, including Malassezia, Candida, Streptococcus and Staphylococcus species, are associated with provocation and/or exacerbation of psoriasis, a detailed analysis of the cutaneous fungal microbiome in psoriatic patients has yet to be performed. To identify the disease-specific fungal microbiota on psoriatic scale samples, fungal rRNA gene sequences from 12 psoriatic patients and 12 healthy controls were analyzed by pyrosequencing. A total of 317 806 high-quality sequences were obtained, representing 142 genera. Malassezia species were the most abundant sequences in both populations (46.9 ± 14.0% in psoriasis vs. 76.0 ± 14.6% for healthy controls). Principal coordinate analysis revealed that the fungal microbiomes were independent. Although an association between the cutaneous fungal microbiome and psoriasis has yet to be established, our data indicate that the microbiome in patients with psoriasis is independent of that in healthy controls.

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