N. Malchin

A phenotype combining hidradenitis suppurativa with Dowling‐Degos disease caused by a founder mutation in PSENEN

Dowling–Degos disease (DDD), featuring reticulate pigmentation, and familial hidradenitis suppurativa (HS) share many clinical features including autosomal dominant inheritance, flexural location and follicular defects. The coexistence of the two disorders was recently found to result from mutations in PSENEN, encoding the γ‐secretase subunit protein presenilin enhancer.

Mutations in TSPEAR, Encoding a Regulator of Notch Signaling, Affect Tooth and Hair Follicle Morphogenesis

Despite recent advances in our understanding of the pathogenesis of ectodermal dysplasias (EDs), the molecular basis of many of these disorders remains unknown. In the present study, we aimed at elucidating the genetic basis of a new form of ED featuring facial dysmorphism, scalp hypotrichosis and hypodontia. Using whole exome sequencing, we identified 2 frameshift and 2 missense mutations in TSPEAR segregating with the disease phenotype in 3 families. TSPEAR encodes the thrombospondin-type laminin G domain and EAR repeats (TSPEAR) protein, whose function is poorly understood. TSPEAR knock-down resulted in altered expression of genes known to be regulated by NOTCH and to be involved in murine hair and tooth development. Pathway analysis confirmed that down-regulation of TSPEAR in keratinocytes is likely to affect Notch signaling. Accordingly, using a luciferase-based reporter assay, we showed that TSPEAR knock-down is associated with decreased Notch signaling. In addition, NOTCH1 protein expression was reduced in patient scalp skin. Moreover, TSPEAR silencing in mouse hair follicle organ cultures was found to induce apoptosis in follicular epithelial cells, resulting in decreased hair bulb diameter. Collectively, these observations indicate that TSPEAR plays a critical, previously unrecognized role in human tooth and hair follicle morphogenesis through regulation of the Notch signaling pathway.

Filaggrin 2 deficiency results in abnormal cell-cell adhesion in the cornified cell layers and causes peeling skin syndrome type A

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.

Punctate palmoplantar keratoderma: an unusual mutation causing an unusual phenotype

Palmoplantar keratodermas (PPKs, OMIM #144200) refers to a large phenotypically and genetically heterogeneous group of keratinization disorders characterized by marked hyperkeratosis on the surface of palms and soles. Punctate PPK (PPKP) features multiple hyperkeratotic papules that develop in early adolescence or later and are irregularly distributed on the palms and soles. The disease is clinically classified into three autosomal dominant subtypes: PPKP1 (OMIM #148600, 614936) characterized by multiple tiny punctate keratoses and caused by mutations in the AAGAB or COL14A1 genes; PPKP2 (OMIM #175860) which features tiny hyperkeratotic spinous papules and PPKP3 or acrokeratoelastoidosis (AKE, OMIM # 101850) which manifests with small hyperkeratotic papules located over the peripheral margins of the palms and soles and is typically associated with degeneration of elastic fibers on histology. The molecular etiology of PPKP2 and AKE remains unknown. This article is protected by copyright. All rights reserved.

SVEP1 plays a crucial role in epidermal differentiation

SVEP1 is a recently identified multidomain cell adhesion protein, homologous to the mouse polydom protein, which has been shown to mediate cell‐cell adhesion in an integrin‐dependent manner in osteogenic cells. In this study, we characterized SVEP1 function in the epidermis. SVEP1 was found by qRT‐PCR to be ubiquitously expressed in human tissues, including the skin. Confocal microscopy revealed that SVEP1 is normally mostly expressed in the cytoplasm of basal and suprabasal epidermal cells. Downregulation of SVEP1 expression in primary keratinocytes resulted in decreased expression of major epidermal differentiation markers. Similarly, SVEP1 downregulation was associated with disturbed differentiation and marked epidermal acanthosis in three‐dimensional skin equivalents. In contrast, the dispase assay failed to demonstrate significant differences in adhesion between keratinocytes expressing normal vs low levels of SVEP1. Homozygous Svep1 knockout mice were embryonic lethal. Thus, to assess the importance of SVEP1 for normal skin homoeostasis in vivo, we downregulated SVEP1 in zebrafish embryos with a Svep1‐specific splice morpholino. Scanning electron microscopy revealed a rugged epidermis with perturbed microridge formation in the centre of the keratinocytes of morphant larvae. Transmission electron microscopy analysis demonstrated abnormal epidermal cell‐cell adhesion with disadhesion between cells in Svep1‐deficient morphant larvae compared to controls. In summary, our results indicate that SVEP1 plays a critical role during epidermal differentiation.

Epidermolytic Ichthyosis Sine Epidermolysis

Abstract: Epidermolytic ichthyosis (EI) is a rare disorder of cornification caused by mutations in KRT1 and KRT10, encoding two suprabasal epidermal keratins. Because of the variable clinical features and severity of the disease, histopathology is often required to correctly direct the molecular analysis. EI is characterized by hyperkeratosis and vacuolar degeneration of the upper epidermis, also known as epidermolytic hyperkeratosis, hence the name of the disease. In the current report, the authors describe members of 2 families presenting with clinical features consistent with EI. The patients were shown to carry classical mutations in KRT1 or KRT10, but did not display epidermolytic changes on histology. These observations underscore the need to remain aware of the limitations of pathological features when considering a diagnosis of EI.

A novel homozygous deletion in EXPH5 causes a skin fragility phenotype

Epidermolysis bullosa simplex (EBS) is the most common form of EB. Eight different genes have been implicated in the pathogenesis of different types of EBS, but a substantial portion of the cases cannot be attributed to mutations in known genes. Recently, recessive mutations in the gene EXPH5 (encoding exophilin‐5, also known as Slac2‐b) were identified in patients affected with a mild form of EBS. We used immunohistochemistry, Sanger sequencing and PCR–restriction fragment length polymorphism analysis to identify the cause of mild congenital skin fragility in a 3‐year‐old girl. No mutations were detected in KRT5 or KRT14, but we identified a novel homozygous deletion in EXPH5, which was found to cosegregate with the disease phenotype in the family. Our results further expand the spectrum of mutations in EXPH5. Appraisal of the present case against previously reported patients indicate that EXPH5 mutations result in a distinctive skin fragility phenotype, with minimal blistering compared with other forms of basal EBS.

Recessive epidermolytic ichthyosis results from loss of keratin 10 expression, regardless of the mutation location

Epidermolytic ichthyosis (EI) is a rare skin disorder caused by mutations in the genes KRT1 and KRT10, and is usually inherited in an autosomal dominant fashion. Only five recessive mutations causing EI have been described, all of which are located in the central region of the KRT10 gene. In the current study, we aimed to identify the genetic defect underlying EI in a 12‐year‐old patient. Direct sequencing of the patients genomic DNA revealed a novel homozygous nonsense mutation residing within the proximal part KRT10 first exon. The mutation was found to co‐segregate with the disease phenotype in an autosomal recessive fashion. Using real‐time quantitative PCR, we found an almost two‐fold decrease in KRT10 expression in the patients skin compared with the skin of healthy controls. Western blot analysis showed complete absence of keratin 10 protein in the patients skin, suggesting early protein degradation.

Striate palmoplantar keratoderma resulting from a missense mutation in DSG1

palmoplantar keratodermas (PPKs, OMIM #144200) refer to a large phenotypically and genetically heterogeneous group of keratinisation disorders characterised by marked hyperkeratosis on the surface of the palms and soles. This article is protected by copyright. All rights reserved.

Identification of a recurrent mutation in ATP2C1 demonstrates that papular acantholytic dyskeratosis and Hailey-Hailey disease are allelic disorders

Papular acantholytic dyskeratosis (PAD), sometimes referred to as PAD of the vulvocrural or anogenital area, is an exceedingly rare skin condition, which usually presents in adulthood and features multiple, asymptomatic or pruritic, skin-colored to whitish papules, located in the groin area. PAD exhibits histological features resembling Darier disease (DD) or Hailey-Hailey disease (HHD), including acantholysis, dyskeratosis as well as hyperkeratosis and parakeratosis, but differs from these disorders by absence of family history and confinement of the lesions Although previously suggested to be a mosaic form of DD, several studies have demonstrated that PAD is caused by mutations in the ATP2C1 gene, encoding the Golgi hSPCA1 pump, which is defective in HHD, thus suggesting PAD is a variant of HHD or that the two diseases belong to the same clinical spectrum. This article is protected by copyright. All rights reserved.