A Novel Recessive Connexin 31 (GJB3) Mutation in a Case of Erythrokeratodermia Variabilis

Partial Loss of Function ABCA12 Mutations Generate Reduced Deposition of Glucosyl-Ceramide, Leading to Patchy Ichthyosis and Erythrodermia Resembling Erythrokeratodermia Variabilis et Progressiva (EKVP)

Ichthyoses are genetically determined cornification disorders of the epidermis characterized by the presence of different degrees of scaling, hyperkeratosis, and erythroderma often associated with palmoplantar keratoderma. Different classifications of these diseases have been proposed, often based upon the involved genes and/or the clinical presentation. The clinical features of these diseases present some overlap of phenotypes among distinct genetic entities, depending mainly on the penetrance of mutations. In this study, using a clinical, genetic, and molecular approach, we analyzed a family with two affected members who had clinical and histological features resembling erythrokeratodermia variabilis (EKV) or a type of erythrodermic hyperkeratosis with palmoplantar keratoderma. Despite of the clinical presentation, we demonstrated that the affected patients were genetically double heterozygous for two different mutations in the ABCA12 gene, known to be responsible for harlequin ichthyosis. To explain the mild phenotype of our patients, we performed a molecular characterization of the skin. In the upper layers of the epidermis, the results showed a patchy presence of the glucosyl-ceramides (GlcCer), which is the lipid transported by ABCA12, fundamental in contributing to skin impermeability. Indeed, the two mutations detected do not completely abolish ABCA12 activity, indicating that the mild phenotype is due to a partial loss of function of the enzyme, thus giving rise to an intermediate phenotype resembling EKVP, due to a partial depletion of GlcCer deposition.

A Connexin Gene (GJB3) Mutation in a Chinese Family With Erythrokeratodermia Variabilis, Ichthyosis and Nonsyndromic Hearing Loss: Case Report and Mutations Update

Background: Gap junctions formed by connexins are channels on cytoplasm functioning in ion recycling and homeostasis. Some members of connexin family including connexin 31 are significant components in human skin and cochlea. In clinic, mutations of connexin 31 have been revealed as the cause of a rare hereditary skin disease called erythrokeratodermia variabilis (EKV) and non-syndromic hearing loss (NSHL).

Objective: To determine the underlying genetic cause of EKV, ichthyosis and NSHL in three members of a Chinese pedigree and skin histologic characteristics of the EKV patient.

Methods: By performing whole exome sequencing (WES), Sanger sequencing and skin biopsy, we demonstrate a Chinese pedigree carrying a mutation of GJB3 with three patients separately diagnosed with EKV, ichthyosis and NSHL.

Results: The proband, a 6-year-old Chinese girl, presented with demarcated annular red-brown plaques and hyperkeratotic scaly patches on her trunk and limbs. Her mother has ichthyosis with hyperkeratosis and geographic tongue while her younger brother had NSHL since birth. Mutation analysis revealed all of them carried a heterozygous missense mutation c.293G>A of GJB3. Skin biopsy showed many grain cells with dyskeratosis in the granular layer. Acanthosis, papillomatosis, and a mild superficial perivascular lymphocytic infiltrate were observed.

Conclusion: A mutation of GJB3 associated with EKV, ichthyosis and NSHL is reported in this case. The daughter with EKV and the son with NSHL in this Chinese family inherited the mutation from their mother with ichthyosis. The variation of clinical features may involve with genetic, epigenetic and environmental factors.

Erythrokeratodermia variabilis et progressiva due to a novel mutation in GJB4

Erythrokeratodermia variabilis et progressiva (EKVP) is a rare genodermatosis of clinical and genetic heterogeneity, characterized by the manifestations of localized or disseminated persistent hyperkeratotic plagues and stationary to migratory transient erythematous patches. The majority of EKVP cases display an autosomal dominant mode of inheritance with incomplete penetrance, although recessive transmission has also been described. Mutations associated with EKVP have been primarily detected in connexin (Cx) genes. We herein reported a Chinese sporadic case of late-onset EKVP with a novel heterozygous missense mutation c.109G>A (p.V37M) in GJB4 (Cx30.3) gene, which resulted in a significant reduction of GJB4 expression in the epidermis of the patient. In accordance, while wild-type GJB4 localized at the cell membrane of HeLa cells forming intercellular junctions and intracellular puncta, V37M mutant variant was diffusely expressed within HeLa cells at a considerably lower level. Our findings reveal an essential role of GJB4 in the pathogenesis of EKVP and provides insights into the therapeutic potential of the disease.

А case of erythrokeratodermia variabilis (Mendes da Costa type) in a three-year-old child

The authors describe a case of erythrokeratodermia variabilis (Mendes da Costa type) in a three-year-old child. They present data on the clinical picture and histological examination. Major stages of the etiology and pathogenesis of the diseases are described.

Erythrokeratoderma variabilis caused by a recessive mutation in GJB3

BACKGROUND

Erythrokeratoderma variabilis (EKV) is a rare disorder of cornification usually associated with dominant mutations in the genes GJB3 and GJB4, which code for connexin (Cx)31 and Cx30.3, respectively, and contribute to the formation of functional gap junctions in the epidermis.

AIM

To identify the molecular basis of recessive EKV in a consanguineous family of Middle Eastern origin.

METHODS

Direct sequencing and site-directed mutagenesis was used to search for the disease-causing mutation and identify its molecular consequences.

RESULTS

A novel missense mutation (c.G88A) was found in the human GJB3 gene, resulting in substitution of the amino acid isoleucine for valine at position 30 (p.V30I). Under in vitro conditions, p.V30I prevents Cx31 reaching the cell membrane and taking part in gap-junction formation.

CONCLUSIONS

Autosomal recessive inheritance should be considered when providing genetic counselling to consanguineous families at risk for EKV.

Connexin 26 (GJB2) mutations, causing KID Syndrome, are associated with cell death due to calcium gating deregulation

The autosomic dominant KID Syndrome (MIM 148210), due to mutations in GJB2 (connexin 26, Cx26), is an ectodermal dysplasia with erythematous scaly skin lesions, keratitis and severe bilateral sensorineural deafness. The Cx26 protein is a component of gap junction channels in epithelia, including the cochlea, which coordinates the exchange of molecules and ions. Here, we demonstrate that different Cx26 mutants (Cx26D50N and Cx26G11E) cause cell death in vitro by the alteration of intra-cellular calcium concentrations. These results help to explain the pathogenesis of both the hearing and skin phenotypes, since calcium is also a potent regulator of the epidermal differentiation process.

Genetic diseases of junctions

Tight junctions, gap junctions, adherens junctions, and desmosomes represent intricate structural intercellular channels and bridges that are present in several tissues, including epidermis. Clues to the important function of these units in epithelial cell biology have been gleaned from a variety of studies including naturally occurring and engineered mutations, animal models and other in vitro experiments. In this review, we focus on mutations that have been detected in human diseases. These observations provide intriguing insight into the biological complexities of cell-cell contact and intercellular communication as well as demonstrating the spectrum of inherited human diseases that are associated with mutations in genes encoding the component proteins. Over the last decade or so, human gene mutations have been reported in four tight junction proteins (claudin 1, 14, 16, and zona occludens 2), nine gap junction proteins (connexin 26, 30, 30.3, 31, 32, 40, 43, 46, and 50), one adherens junction protein (P-cadherin) and eight components of desmosomes (plakophilin (PKP) 1 and 2, desmoplakin, plakoglobin--which is also present in adherens junctions, desmoglein (DSG) 1, 2, 4, and corneodesmosin). These discoveries have often highlighted novel or unusual phenotypes, including abnormal skin barrier function, alterations in epidermal differentiation, and developmental anomalies of various ectodermal appendages, especially hair, as well as a range of extracutaneous pathologies. However, this review focuses mainly on inherited disorders of junctions that have an abnormal skin phenotype.

Clinical and Genetic Heterogeneity of Erythrokeratoderma Variabilis

The skin disease erythrokeratoderma variabilis (EKV) has been shown to be associated with mutations in GJB3 and GJB4 encoding connexin (Cx)31 and Cx30.3, respectively. Gap junctions composed of Cx proteins are intracellular channels providing a mechanism of synchronized cellular response facilitating metabolic and electronic functions of the cell. In the skin, Cx31 and Cx30.3 are expressed in the stratum granulosum of the epidermis with a suggested role in late keratinocyte differentiation. Molecular investigations of GJB3 and GJB4 were performed in five pedigrees and three sporadic cases of EKV. Mutational analyzes revealed disease-associated Cx31 or Cx30.3 mutations in only three probands of which two were novel mutations and one was a recurrent mutation. These genetic studies further demonstrate the heterogeneous nature of the erythrokeratodermas as not all individuals that were clinically diagnosed with EKV harbor Cx31 or Cx30.3 mutations.

Erythrokeratodermas: A classification in a state of flux?

The term 'erythrokeratodermas' or 'erythrokeratodermias' has been applied to a group of inherited disorders characterized by well-demarcated erythematous lesions and hyperkeratotic plaques. Connexin mutations have been demonstrated to be responsible for most cases of erythrokeratoderma variabilis but there remain some cases without demonstrated connexin mutations, suggesting genetic heterogeneity. The position of progressive symmetric erythrokeratoderma has become rather unclear. Loricin mutations have been found in some cases that clinically resemble variant Vohwinkel syndrome and other cases have features that overlap with those of erythrokeratoderma variablis. Whether progressive symmetric erythrokeratoderma exists as a distinct entity is under question.

A new, recurrent mutation of GJB3 (Cx31) in erythrokeratodermia variabilis

BACKGROUND

Erythrokeratodermia variabilis (EKV) is an autosomal dominant or recessive genodermatosis characterized by the coexistence of randomly occurring, transient, erythematous patches and hyperkeratosis of the skin. The disorder has been mapped to chromosome 1p35.1 but is genetically heterogeneous. EKV may be caused by pathogenic mutations in one of two neighbouring connexin genes, GJB3 and GJB4, encoding the gap junction proteins Cx31 and Cx30.3, respectively. Twelve distinct mutations identified to date cluster either at the cytoplasmic amino-terminus or in the four transmembrane domains.

OBJECTIVES

To report a large family with EKV and an unrelated sporadic case.

METHODS

DNA amplification and mutation analysis, followed by denaturing high-performance liquid chromatography to confirm the segregation of the mutations in the two families with EKV.

RESULTS

A novel, recurrent GJB3 mutation (625C-->T; L209F) was identified in the family with EKV and in the unrelated sporadic case.

CONCLUSIONS

This mutation is the first to affect a conserved residue in the cytoplasmic carboxy-terminus of any connexin gene with a cutaneous phenotype, emphasizing its structural and/or functional importance.

Connexin disorders of the skin

Over the past decade, the molecular basis of most disorders of cornification has been unveiled. Among these, a distinct group has emerged because of primary defects in cell-cell communication due to faulty gap junction proteins also known as connexins. This review aims to delineate the cutaneous connexin disorders and to highlight intriguing genotype-phenotype correlations and emanating clinical implications.