ITGB4-associated non-Herlitz junctional epidermolysis bullosa: report of two new cases carrying two novel ITGB4 mutations

Identification of novel compound heterozygous ITGB4 mutations in a Chinese woman with junctional epidermolysis bullosa without pylori atresia but profound urinary symptoms: A case report and review of the literature

Loss of α6 and β4 integrin expression caused by germ line mutations in ITGA6 and ITGB4 usually leads to junctional epidermolysis bullosa (JEB) with pyloric atresia (PA) (JEB-PA; Online Mendelian Inheritance in Man #226730). However, recent studies have suggested that integrin-associated JEB may occur without PA but with other symptoms of the epithelial tissues. Here, we present a case of a Chinese woman with JEB without PA but with profound urinary symptoms. Mutation analysis revealed that the patient carried compound heterozygous mutations in the ITGB4 gene: a frameshift mutation c.600dupC (p.Phe201Leufs*15) and a novel missense mutation c.599C>G (p.Pro200Arg). Our report not only raises the question of whether the designation JEB-PA is appropriate, but also expands our current knowledge of the ITGB4 mutation spectrum.

Identification and Computational Analysis of Novel Pathogenic Variants in Pakistani Families with Diverse Epidermolysis Bullosa Phenotypes

Epidermolysis bullosa (EB) includes a group of rare gesnodermatoses that result in blistering and erosions of the skin and mucous membranes. Genetically, pathogenic variants in around 20 genes are known to alter the structural and functional integrity of intraepidermal adhesion and dermo-epidermal anchorage, leading to four different types of EB. Here we report the underlying genetic causes of EB phenotypes segregating in seven large consanguineous families, recruited from different regions of Pakistan. Whole exome sequencing, followed by segregation analysis of candidate variants through Sanger sequencing, identified eight pathogenic variants, including three novel (ITGB4: c.1285G>T, and c.3373G>A; PLEC: c.1828A>G) and five previously reported variants (COL7A1: c.6209G>A, and c.1573C>T; FERMT1: c.676insC; LAMA3: c.151insG; LAMB3: c.1705C>T). All identified variants were either absent or had very low frequencies in the control databases. Our in-silico analyses and 3-dimensional (3D) molecular modeling support the deleterious impact of these variants on the encoded proteins. Intriguingly, we report the first case of a recessively inherited form of rare EBS-Ogna associated with a homozygous variant in the PLEC gene. Our study highlights the clinical and genetic diversity of EB in the Pakistani population and expands the mutation spectrum of EB; it could also be useful for prenatal diagnosis and genetic counseling of the affected families.

Identification of two rare and novel large deletions in ITGB4 gene causing epidermolysis bullosa with pyloric atresia

Epidermolysis bullosa with pyloric atresia (EB-PA) is a rare autosomal recessive hereditary disease with a variable prognosis from lethal to very mild. EB-PA is classified into Simplex form (EBS-PA: OMIM #612138) and Junctional form (JEB-PA: OMIM #226730), and it is caused by mutations in ITGA6, ITGB4 and PLEC genes. We report the analysis of six patients with EB-PA, including two dizygotic twins. Skin immunofluorescence epitope mapping was performed followed by PCR and direct sequencing of the ITGB4 gene. Two of the patients presented with non-lethal EB-PA associated with missense ITGB4 gene mutations. For the other four, early postnatal demise was associated with complete lack of β4 integrin due to a variety of ITGB4 novel mutations (2 large deletions, 1 splice-site mutation and 3 missense mutations). One of the deletions spanned 278 bp, being one of the largest reported to date for this gene. Remarkably, we also found for the first time a founder effect for one novel mutation in the ITGB4 gene. We have identified 6 novel mutations in the ITGB4 gene to be added to the mutation database. Our results reveal genotype-phenotype correlations that contribute to the molecular understanding of this heterogeneous disease, a pivotal issue for prognosis and for the development of novel evidence-based therapeutic options for EB management.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

Blistering disease: insight from the hemidesmosome and other components of the dermal-epidermal junction

The hemidesmosome is a specialized transmembrane complex that mediates the binding of epithelial cells to the underlying basement membrane. In the skin, this multiprotein structure can be regarded as the chief adhesion unit at the site of the dermal-epidermal junction. Focal adhesions are additional specialized attachment structures located between hemidesmosomes. The integrity of the skin relies on well-assembled and functional hemidesmosomes and focal adhesions (also known as integrin adhesomes). However, if these adhesion structures are impaired, e.g., as a result of circulating autoantibodies or inherited genetic mutations, the mechanical strength of the skin is compromised, leading to blistering and/or tissue inflammation. A particular clinical presentation emerges subject to the molecule that is targeted. None of these junctional complexes are simply compounds of adhesion molecules; they also play a significant role in signalling pathways involved in the differentiation and migration of epithelial cells such as during wound healing and in tumour invasion. We summarize current knowledge about hereditary and acquired blistering diseases emerging from pathologies of the hemidesmosome and its neighbouring proteins as components of the dermal-epidermal junction.

Phenotypic spectrum of epidermolysis bullosa associated with α6β4 integrin mutations

BACKGROUND

Integrin α6β4 is a transmembrane receptor and a key component of the hemidesmosome anchoring complex. It is involved in cell-matrix adhesion and signalling in various tissues. Mutations in the ITGA6 and ITGB4 genes coding for α6β4 integrin compromise dermal-epidermal adhesion and are associated with skin blistering and pyloric atresia (PA), a disorder known as epidermolysis bullosa with PA (EB-PA).

OBJECTIVES

To elucidate the molecular pathology of skin fragility in eight cases, disclose the underlying ITGA6 and ITGB4 mutations and study genotype-phenotype correlations.

METHODS

DNA was isolated from ethylenediaminetetraacetic acid-blood samples, and the coding exons and exon-intron boundaries of ITGA6 and ITGB4 were amplified by polymerase chain reaction (PCR), and directly sequenced. Skin samples were submitted to immunofluorescence mapping with antibodies to adhesion proteins of the dermal-epidermal junction. Primary keratinocytes were isolated, and used for RNA and protein extraction, reverse transcription PCR and immunoblotting. Ultrastructural analysis of the skin was performed in one patient.

RESULTS

We disclose 10 novel mutations, one in ITGA6 and nine in ITGB4. Skin cleavage was either intraepidermal or junctional. Lethal outcome and PA correlated with loss-of-function mutations in two cases. Solely mild skin involvement was associated with deletion of the C-terminus of β4 integrin. Combinations of missense, nonsense or frameshift mutations caused severe urinary tract involvement in addition to skin fragility in five cases.

CONCLUSIONS

The present study reveals novel ITGA6 and ITGB4 gene mutations and supports previous reports showing that the phenotype may lack PA and be limited to skin and nail involvement. In four out of six cases of EB-PA, life expectancy was not impaired. A high frequency of urinary tract involvement was found in this study, and represented the main cause of morbidity. Low levels of β4 integrin expression were compatible with hemidesmosomal integrity and a mild skin phenotype.

Beyond expectations: novel insights into epidermal keratin function and regulation

The epidermis is a stratified epithelium that relies on its cytoskeleton and cell junctions to protect the body against mechanical injury, dehydration, and infections. Keratin intermediate filament proteins are involved in many of these functions by forming cell-specific cytoskeletal scaffolds crucial for the maintenance of cell and tissue integrity. In response to various stresses, the expression and organization of keratins are altered at transcriptional and posttranslational levels to restore tissue homeostasis. Failure to restore tissue homeostasis in the presence of keratin gene mutations results in acute and chronic skin disorders for which currently no rational therapies are available. Here, we review the recent progress on the role of keratins in cytoarchitecture, adhesion, signaling, and inflammation. By focusing on epidermal keratins, we illustrate the contribution of keratin isotypes to differentiated epithelial functions.

Disorders of the cutaneous basement membrane zone--the paradigm of epidermolysis bullosa

The cutaneous basement membrane zone (BMZ) is a highly specialized functional complex that provides the skin with structural adhesion and resistance to shearing forces. Its regulatory functions include control of epithelial-mesenchymal interactions under physiological and pathological conditions. Mutations in genes encoding components of the BMZ are associated with inherited skin disorders of the epidermolysis bullosa (EB) group, characterized by skin fragility, mechanically induced blisters and erosions of the skin and mucous membranes. Although most disease-associated genes are known, the genetic basis of new EB subtypes linked to mutations in genes for focal adhesion proteins was uncovered only recently. The molecular mechanisms leading to blistering, abnormal wound healing, predisposition to skin cancer, and other complications in EB have been elucidated using animal models and disease proteomics. The rapid progress in understanding the molecular basis of EB has enabled the development of strategies for biologically valid causal therapies.