The genetic background of generalized pustular psoriasis: IL36RN mutations and CARD14 gain-of-function variants.

Generalized pustular psoriasis (GPP) is often present in patients with existing or prior psoriasis vulgaris (PV; "GPP with PV"). However, cases of GPP have been known to arise without a history of PV ("GPP alone"). There has long been debate over whether GPP alone and GPP with PV are distinct subtypes that are etiologically different from each other. We recently reported that the majority of GPP alone cases is caused by recessive mutations of IL36RN. In contrast, only a few exceptional cases of GPP with PV were found to have recessive IL36RN mutations. Very recently, we also reported that CARD14 p.Asp176His, a gain-of-function variant, is a predisposing factor for GPP with PV; in contrast, the variant is not associated with GPP alone in the Japanese population. These results suggest that GPP alone is genetically different from GPP with PV. IL36RN mutations are also found in some patients with severe acute generalized exanthematous pustulosis, palmar-plantar pustulosis, and acrodermatitis continua of hallopeau. CARD14 mutations and variants are causal or disease susceptibility factors of PV, GPP, or pityriasis rubra pilaris, depending on the mutation or variant position of CARD14. It is clinically important to analyze IL36RN mutations in patients with sterile pustulosis. For example, identifying recessive IL36RN mutations leads to early diagnosis of GPP, even at the first episode of pustulosis. In addition, individuals with IL36RN mutations are very susceptible to GPP or GPP-related generalized pustulosis induced by drugs (e.g., amoxicillin), infections, pregnancy, or menstruation.