No abstract

The present data confirm the genetic basis of the combined DDD-HS phenotype and suggest that Notch signalling may play a central role in the pathogenesis of this rare condition.

Background: Atopic dermatitis (AD) is a highly prevalent chronic inflammatory skin disease that is known to be, at least in part, genetically determined. Mutations in caspase recruitment domain-containing protein 14 (CARD14) have been shown to result in various forms of psoriasis and related disorders. Objective: We aimed to identify rare DNA variants conferring a significant risk for AD through genetic and functional studies in a cohort of patients affected with severe AD. Methods: Whole-exome and direct gene sequencing, immunohistochemistry, real-time PCR, ELISA, and functional assays in human keratinocytes were used. Results: In a cohort of patients referred with severe AD, DNA sequencing revealed in 4 patients 2 rare heterozygous missense mutations in the gene encoding CARD14, a major regulator of nuclear factor kB (NF-kB). A dual luciferase reporter assay demonstrated that both mutations exert a dominant loss-offunction effect and result in decreased NF-kB signaling.

Peeling skin syndromes form a large and heterogeneous group of inherited disorders characterized by superficial detachment of the epidermal cornified cell layers, often associated with inflammatory features. Here we report on a consanguineous family featuring noninflammatory peeling of the skin exacerbated by exposure to heat and mechanical stress. Whole exome sequencing revealed a homozygous nonsense mutation in FLG2, encoding filaggrin 2, which cosegregated with the disease phenotype in the family. The mutation was found to result in decreased FLG2 RNA levels as well as almost total absence of filaggrin 2 in the patient epidermis. Filaggrin 2 was found to be expressed throughout the cornified cell layers and to colocalize with corneodesmosin that plays a crucial role in maintaining cell-cell adhesion in this region of the epidermis. The absence of filaggrin 2 in the patient skin was associated with markedly decreased corneodesmosin expression, which may contribute to the peeling phenotype displayed by the patients. Accordingly, using the dispase dissociation assay, we showed that FLG2 downregulation interferes with keratinocyte cell-cell adhesion. Of particular interest, this effect was aggravated by temperature elevation, consistent with the clinical phenotype. Restoration of corneodesmosin levels by ectopic expression rescued cell-cell adhesion. Taken together, the present data suggest that filaggrin 2 is essential for normal cell-cell adhesion in the cornified cell layers.