Striate palmoplantar keratoderma resulting from a frameshift mutation in the desmoglein 1 gene

Striate palmoplantar keratoderma: a novel DSG1 mutation, combined with an LDLR mutation

BACKGROUND

Palmoplantar keratoderma (PPK) is a heterogeneous group of disorders characterized by abnormal thickening of the skin on the palms and soles. Striate palmoplantar keratoderma (SPPK) is commonly caused by heterozygous mutations in the desmoglein-1 (DSG1) gene.

OBJECTIVE

This study aimed to report a case of a 36-year-old Chinese female patient with SPPK caused by a novel DSG1 gene mutation, along with her family history, and explore its potential relationship with other genetic variants.

METHODS

Whole-exome sequencing was performed on the patient and their family members to identify the pathogenic mutation, which was validated by Sanger sequencing. Histological and electron microscopy analyses were conducted to examine the pathological characteristics of skin tissue.of skin tissue.

RESULTS

A frameshift mutation, c.1285del, in exon 10 of the DSG1 gene was identified, leading to a loss of protein function and resulting in SPPK. This mutation was also detected in two other family members with similar phenotypes. Additionally, a classical splicing variant, c.313+2dup, in the low-density lipoprotein receptor (LDLR) gene associated with hypercholesterolemia was identified in the patient; however, no direct association with SPPK was observed.

CONCLUSION

This study was the first to report a novel mutation in the DSG1 gene associated with SPPK and suggested a potential role of the LDLR gene variant in SPPK patients, providing new insights for further research into the genetic mechanisms underlying SPPK.

CASTing the net wider: A case report of PLACK syndrome associated with dilated cardiomyopathy

PLACK syndrome (OMIM 616295) is a rare genodermatosis associated with peeling skin, leukonychia, acral punctate keratosis, cheilitis, and knuckle pads and is caused by loss-of-function mutations in the CAST gene, which encodes calpastatin, a calcium-dependent protease. This case report highlights a case of PLACK syndrome presenting with the unique findings of striate hyperkeratosis on the palms as well as life-threatening cardiomyopathy. We review why CAST mutations might impact cardiac function and raise awareness of the potential association between PLACK syndrome and cardiac manifestations.

Myocardial Damage in a Highly Suspected Case With Paraneoplastic Pemphigus: A Case Report and Literature Review

Paraneoplastic pemphigus (PNP) is a rare mucocutaneous autoimmune disease. It has multiple clinical accompanied symptoms by affecting various types of epithelia, including the gastrointestinal and respiratory tract. However, an extensive review of the literature found no cases of PNP associated with myocardial damage. Here, we present a 56-year-old male patient with clinically and histopathologically typical paraneoplastic pemphigus (PNP), who had sustained myocardial injury due to non-cardiac disease involvement. Therefore, we suppose that, when persistent cardiac necrosis markers are elevated in patients with paraneoplastic pemphigus (PNP), the possibility of concomitant myocardial damage should get more attention from clinicians to obtain quick diagnosis and treatment.

Mutations in genes encoding desmosomal proteins: spectrum of cutaneous and extracutaneous abnormalities

The desmosome is a type of intercellular junction found in epithelial cells, cardiomyocytes and other specialized cell types. Composed of a network of transmembranous cadherins and intracellular armadillo, plakin and other proteins, desmosomes contribute to cell-cell adhesion, signalling, development and differentiation. Mutations in genes encoding desmosomal proteins result in a spectrum of erosive skin and mucosal phenotypes that also may affect hair or heart. This review summarizes the molecular pathology and phenotypes associated with desmosomal dysfunction with a focus on inherited disorders that involve the skin/hair, as well as associated extracutaneous pathologies. We reviewed the relevant literature to collate studies of pathogenic human mutations in desmosomes that have been reported over the last 25 years. Mutations in 12 different desmosome genes have been documented, with mutations in nine genes affecting the skin/mucous membranes (DSG1, DSG3, DSC2, DSC3, JUP, PKP1, DSP, CDSN, PERP) and eight resulting in hair abnormalities (DSG4, DSC2, DSC3, JUP, PKP1, DSP, CDSN, PERP). Mutations in three genes can result in cardiocutaneous syndromes (DSC2, JUP, DSP), although mutations have been described in five genes in inherited heart disorders that may lack any dermatological manifestations (DSG2, DSC2, JUP, PKP2, DSP). Understanding the diverse nature of these clinical phenotypes, as well as the desmosome gene mutation(s), has clinical value in managing and counselling patients, as well as demonstrating the biological role and activity of specific components of desmosomes in skin and other tissues.

Pathophysiology of the Desmo-Adhesome

Advances in our understanding of desmosomal diseases have provided a clear demonstration of the key role played by desmosomes in tissue and organ physiology, highlighting the importance of their dynamic and finely regulated structure. In this context, non-desmosomal regulatory molecules have acquired increasing relevance in the study of this organelle resulting in extending the desmosomal interactome, named the "desmo-adhesome." Spatiotemporal changes in the expression and regulation of the desmo-adhesome underlie a number of genetic, infectious, autoimmune, and malignant conditions. The aim of the present article was to examine the structural and functional relationship of the desmosome, by providing a comprehensive, yet focused overview of the constituents targeted in human disease. The inclusion of the novel regulatory network in the desmo-adhesome pathophysiology opens new avenues to a deeper understanding of desmosomal diseases, potentially unveiling pathogenic mechanisms waiting to be explored. J. Cell. Physiol. 232: 496-505, 2017. © 2016 Wiley Periodicals, Inc.

A spontaneous deletion within the desmoglein 3 extracellular domain of mice results in hypomorphic protein expression, immunodeficiency, and a wasting disease phenotype

Desmoglein 3 is a transmembrane component of desmosome complexes that mediate epidermal cell-to-cell adhesion and tissue integrity. Antibody blockade of desmoglein 3 function in pemphigus vulgaris patients leads to skin blistering (acantholysis) and oral mucosa lesions. Desmoglein 3 deficiency in mice leads to a phenotype characterized by cyclic alopecia in addition to the dramatic skin and mucocutaneous acantholysis observed in pemphigus patients. In this study, mice that developed an overt squeaky (sqk) phenotype were identified with obstructed airways, cyclic hair loss, and severe immunodeficiency subsequent to the development of oral lesions and malnutrition. Single-nucleotide polymorphism-based quantitative trait loci mapping revealed a genetic deletion that resulted in expression of a hypomorphic desmoglein 3 protein with a truncation of an extracellular cadherin domain. Because hypomorphic expression of a truncated desmoglein 3 protein led to a spectrum of severe pathology not observed in mice deficient in desmoglein 3, similar human genetic alterations may also disrupt desmosome function and induce a disease course distinct from pathogenesis of pemphigus vulgaris.

Inherited desmosomal disorders

Desmosomes serve as intercellular junctions in various tissues including the skin and the heart where they play a crucial role in cell-cell adhesion, signalling and differentiation. The desmosomes connect the cell surface to the keratin cytoskeleton and are composed of a transmembranal part consisting mainly of desmosomal cadherins, armadillo proteins and desmoplakin, which form the intracytoplasmic desmosomal plaque. Desmosomal genodermatoses are caused by mutations in genes encoding the various desmosomal components. They are characterized by skin, hair and cardiac manifestations occurring in diverse combinations. Their classification into a separate and distinct clinical group not only recognizes their common pathogenesis and facilitates their diagnosis but might also in the future form the basis for the design of novel and targeted therapies for these occasionally life-threatening diseases.

Loss of desmoglein 1 associated with palmoplantar keratoderma, dermatitis and multiple allergies

Monoallelic desmoglein 1 mutations have been known for many years to cause striate palmoplantar keratoderma, but only recently, biallelic loss-of-function mutations were associated with a new disorder, designated as SAM syndrome (comprising severe dermatitis, multiple allergies and metabolic wasting) in two consanguineous families. We report on a new case from a third independent family with the homozygous nonsense mutation, c.2659C>T, p.R887* in exon 15 of DSG1 (desmoglein 1 gene). This mutation led to mRNA decay and loss of expression of desmoglein 1. The clinical phenotype consisted of severe palmoplantar keratoderma, dermatitis and multiple allergies. In contrast to the previous cases, malabsorption, hypoalbuminaemia, developmental delay, hypotrichosis or severe recurrent infections were not observed.

Characterization of desmoglein expression in the normal prostatic gland. Desmoglein 2 is an independent prognostic factor for aggressive prostate cancer

PURPOSE

The expression of desmogleins (DSGs), which are known to be crucial for establishing and maintaining the cell-cell adhesion required for tissue integrity, has been well characterized in the epidermis and hair follicle; however, their expression in other epithelial tissues such as prostate is poorly understood. Although downregulation of classical cadherins, such as E-cadherin, has been described in prostate cancer tissue samples, the expression of desmogleins has only been previously reported in prostate cancer cell lines. In this study we characterized desmoglein expression in normal prostate tissues, and further investigated whether Desmoglein 2 (DSG2) expression specifically can serve as a potential clinical prognostic factor for patients diagnosed with primary prostate cancer.

EXPERIMENTAL DESIGN

We utilized immunofluorescence to examine DSG2 expression in normal prostate (n = 50) and in a clinically well-characterized cohort of prostate cancer patients (n = 414). Correlation of DSG2 expression with clinico-pathological characteristics and biochemical recurrence was analyzed to assess its clinical significance.

RESULTS

These studies revealed that DSG2 and DSG4 were specifically expressed in prostatic luminal cells, whereas basal cells lack their expression. In contrast, DSG1 and DSG3 were not expressed in normal prostate epithelium. Further analyses of DSG2 expression in prostate cancer revealed that reduced levels of this biomarker were a significant independent marker of poor clinical outcome.

CONCLUSION

Here we report for the first time that a low DSG2 expression phenotype is a useful prognostic biomarker of tumor aggressiveness and may serve as an aid in identifying patients with clinically significant prostate cancer.

Desmoglein-1/Erbin interaction suppresses ERK activation to support epidermal differentiation

Genetic disorders of the Ras/MAPK pathway, termed RASopathies, produce numerous abnormalities, including cutaneous keratodermas. The desmosomal cadherin, desmoglein-1 (DSG1), promotes keratinocyte differentiation by attenuating MAPK/ERK signaling and is linked to striate palmoplantar keratoderma (SPPK). This raises the possibility that cutaneous defects associated with SPPK and RASopathies share certain molecular faults. To identify intermediates responsible for executing the inhibition of ERK by DSG1, we conducted a yeast 2-hybrid screen. The screen revealed that Erbin (also known as ERBB2IP), a known ERK regulator, binds DSG1. Erbin silencing disrupted keratinocyte differentiation in culture, mimicking aspects of DSG1 deficiency. Furthermore, ERK inhibition and the induction of differentiation markers by DSG1 required both Erbin and DSG1 domains that participate in binding Erbin. Erbin blocks ERK signaling by interacting with and disrupting Ras-Raf scaffolds mediated by SHOC2, a protein genetically linked to the RASopathy, Noonan-like syndrome with loose anagen hair (NS/LAH). DSG1 overexpression enhanced this inhibitory function, increasing Erbin-SHOC2 interactions and decreasing Ras-SHOC2 interactions. Conversely, analysis of epidermis from DSG1-deficient patients with SPPK demonstrated increased Ras-SHOC2 colocalization and decreased Erbin-SHOC2 colocalization, offering a possible explanation for the observed epidermal defects. These findings suggest a mechanism by which DSG1 and Erbin cooperate to repress MAPK signaling and promote keratinocyte differentiation.

Cardiac autoantibodies from patients affected by a new variant of endemic pemphigus foliaceus in Colombia, South America

Several patients affected by a new variant of endemic pemphigus foliaceus in El Bagre, Colombia (El Bagre-EPF) have experienced a sudden death syndrome, including persons below the age of 50. El Bagre-EPF patients share several autoantigens with paraneoplastic pemphigus patients, such as reactivity to plakins. Further, paraneoplastic pemphigus patients have autoantibodies to the heart. Therefore, we tested 15 El Bagre-EPF patients and 15 controls from the endemic area for autoreactivity to heart tissue using direct and indirect immunofluorescence, confocal microscopy, immunohistochemistry, immunoblotting, and immunoelectron microscopy utilizing heart extracts as antigens. We found that 7 of 15 El Bagre patients exhibited a polyclonal immune response to several cell junctions of the heart, often colocalizing with known markers. These colocalizing markers included those for the area composita of the heart, such as anti-desmoplakins I and II; markers for gap junctions, such as connexin 43; markers for tight junctions, such as ezrin and junctional adhesion molecule A; and adherens junctions, such pan-cadherin. We also detected colocalization of the patient antibodies within blood vessels, Purkinje fibers, and cardiac sarcomeres. We conclude that El Bagre-EPF patients display autoreactivity to multiple cardiac epitopes, that this disease may resemble what is found in patients with rheumatic carditis, and further, that the cardiac pathophysiology of this disorder warrants further evaluation.

RNAi-mediated inhibition of the desmosomal cadherin (desmoglein 3) impairs epithelial cell proliferation

OBJECTIVES

  Desmoglein 3 (Dsg3) is a desmosomal adhesion protein expressed in basal and immediate suprabasal layers of skin. Importance of Dsg3 in cell-cell adhesion and maintenance of tissue integrity is illustrated by findings of keratinocyte dissociation in the autoimmune disease, pemphigus vulgaris, where autoantibodies target Dsg3 on keratinocyte surfaces and cause Dsg3 depletion from desmosomes. However, recognition of possible participation of involvement of Dsg3 in cell proliferation remains controversial. Currently, available evidence suggests that Dsg3 may have both anti- and pro-proliferative roles in keratinocytes. The aim of this study was to use RNA interference (RNAi) strategy to investigate effects of silencing Dsg3 in cell-cell adhesion and cell proliferation in two cell lines, HaCaT and MDCK.

MATERIALS AND METHODS

  Cells were transfected with siRNA, and knockdown of Dsg3 was assessed by western blotting, fluorescence-activated cell sorting and confocal microscopy. Cell-cell adhesion was analysed using the hanging drop/fragmentation assay, and cell proliferation by colony forming efficiency, BrdU incorporation, cell counts and organotypic culture.

RESULTS

  Silencing Dsg3 caused defects in cell-cell adhesion and concomitant reduction in cell proliferation in both HaCaT and MDCK cells.

CONCLUSION

  These findings suggest that Dsg3 depletion by RNAi reduces cell proliferation, which is likely to be secondary to a defect in cell-cell adhesion, an essential function required for cell differentiation and morphogenesis.

Mutations in the desmoglein 1 gene in five Pakistani families with striate palmoplantar keratoderma

BACKGROUND

Striate palmoplantar keratoderma (SPPK; OMIM #148700) is a rare autosomal dominant genodermatosis characterized by linear hyperkeratosis on the digits and hyperkeratosis on the palms and soles. SPPK is known to be caused by heterozygous mutations in either the desmoglein 1 (DSG1), desmoplakin (DSP), or keratin 1 (KRT1) genes.

OBJECTIVE

To define the molecular basis of SPPK in five Pakistani families showing a clear autosomal dominant inheritance pattern of SPPK.

METHODS

Based on previous reports of DSG1 mutations in SPPK, we performed direct sequencing of the DSG1 gene of all five families.

RESULTS

Mutation analysis resulted in the identification of one recurrent mutation (p.R26X) and four novel mutations (c.Ivs4-2A>G, c.515C>T, c.Ivs9-3C>G, and c.1399delA) in the DSG1 gene. Each mutation is predicted to cause haploinsufficiency of DSG1 protein.

CONCLUSION

The results of our study further underscore the significance of the desmoglein gene family in diseases of epidermal integrity.

Novel mutations in DSG1 causing striate palmoplantar keratoderma

BACKGROUND

Striate palmoplantar keratoderma (SPPK) has been shown to be caused by mutations in at least three genes: DSG1, DSP and KRT1.

METHODS

Three families with nine affected members were assessed using a candidate gene-based screening approach.

RESULTS

In all three families, new heterozygous mutations were found in DSG1.

CONCLUSION

Direct sequencing of cDNA derived from affected skin in one patient failed to reveal a pathogenic mutation, suggesting that SPPK results from haploinsufficiency for DSG1.