Autoinflammatory keratinization diseases: An emerging concept encompassing various inflammatory keratinization disorders of the skin

Abstract

Classifying inflammatory skin diseases is challenging, especially for the expanding group of disorders triggered by genetic factors resulting in hyperactivated innate immunity that result in overlapping patterns of dermal and epidermal inflammation with hyperkeratosis. For such conditions, the umbrella term "autoinflammatory keratinization diseases" (AIKD) has been proposed. AIKD encompasses diseases with mixed pathomechanisms of autoinflammation and autoimmunity, and includes IL-36 receptor antagonist (IL-36Ra)-related pustulosis, CARD14-mediated pustular psoriasis, pityriasis rubra pilaris (PRP) type V, and familial keratosis lichenoides chronica (KLC). Mechanistically, the entities include generalized pustular psoriasis (GPP) without psoriasis vulgaris, impetigo herpetiformis and acrodermatitis continua, which are IL-36Ra-related pustuloses caused by loss-of-function mutations in IL36RN; GPP with psoriasis vulgaris and palmoplantar pustular psoriasis which are CARD14-mediated pustular psoriasiform dermatoses with gain-of-function variants of CARD14; PRP type V which is caused by gain-of-function mutations in CARD14; and, familial KLC in which mutations in NLRP1, an inflammasome sensor protein predominantly expressed in skin, have been identified. It is likely that further inflammatory keratinization disorders will also fall within the concept of AIKD, as elucidation of novel pathogenic mechanisms of inflammatory keratinization diseases emerges. A better understanding of the pathophysiology of AIKD is likely to lead to innovative, targeted therapies that benefit patients.

Keywords: Autoinflammation; CARD14; IL-36 receptor antagonist; Keratinization; Keratosis lichenoides chronica; NLRP1; Pityriasis rubra pilaris; Psoriasis; Psoriatic arthritis; Pustular psoriasis.