EBS in Children with De Novo Pathogenic Variants Disturbing Krt14.

Epidermolysis bullosa simplex (EBS) is a dermatological condition marked by skin fragility and blister formation resulting from separation within the basal layer of the epidermis, which can be attributed to various genetic etiologies. This study presents three pathogenic de novo variants in young children, with clinical manifestations appearing as early as the neonatal period. The variants contribute to the EBS phenotype through two distinct mechanisms: direct keratin abnormalities due to pathogenic variants in the Krt14 gene, and indirect effects via pathogenic mutation in the KLHL24 gene, which interfere with the natural proteasome-mediated degradation pathway of KRT14. We report one severe case of EBS with mottled pigmentation arising from the Met119Thr pathogenic variant in KRT14, another case involving a pathogenic KLHL24 Met1Val variant, and a third case featuring the hot spot mutation Arg125His in KRT14, all manifesting within the first few weeks of life. This research underscores the complexity of genetic influences in EBS and highlights the importance of early genetic screening for accurate diagnosis and management.

Allele-specific CRISPR-Cas9 editing of dominant epidermolysis bullosa simplex in human epidermal stem cells.

Epidermolysis bullosa simplex (EBS) is a rare skin disease inherited mostly in an autosomal dominant manner. Patients display a skin fragility that leads to blisters and erosions caused by minor mechanical trauma. EBS phenotypic and genotypic variants are caused by genetic defects in intracellular proteins whose function is to provide the attachment of basal keratinocytes to the basement membrane zone and most EBS cases display mutations in keratin 5 (KRT5) and keratin 14 (KRT14) genes. Besides palliative treatments, there is still no long-lasting effective cure to correct the mutant gene and abolish the dominant negative effect of the pathogenic protein over its wild-type counterpart. Here, we propose a molecular strategy for EBS01 patient's keratinocytes carrying a monoallelic c.475/495del21 mutation in KRT14 exon 1. Through the CRISPR-Cas9 system, we perform a specific cleavage only on the mutant allele and restore a normal cellular phenotype and a correct intermediate filament network, without affecting the epidermal stem cell, referred to as holoclones, which play a crucial role in epidermal regeneration.

Posttranslational modifications of keratins and their associated proteins as therapeutic targets in keratin diseases.

The keratin cytoskeleton protects epithelia against mechanical, nonmechanical, and physical stresses, and participates in multiple signaling pathways that regulate cell integrity and resilience. Keratin gene mutations cause multiple rare monoallelic epithelial diseases termed keratinopathies, including the skin diseases Epidermolysis Bullosa Simplex (EBS) and Pachyonychia Congenita (PC), with limited available therapies. The disease-related keratin mutations trigger posttranslational modifications (PTMs) in keratins and their associated proteins that can aggravate the disease. Recent findings of drug high-throughput screening have led to the identification of compounds that may be repurposed, since they are used for other human diseases, to treat keratinopathies. These drugs target unique PTM pathways and sites, including phosphorylation and acetylation of keratins and their associated proteins, and have shed insights into keratin regulation and interactions. They also offer the prospect of testing the use of drug mixtures, with the long view of possible beneficial human use coupled with increased efficacy and lower side effects.

Dystonin modifiers of junctional epidermolysis bullosa and models of epidermolysis bullosa simplex without dystonia musculorum.

The Lamc2jeb junctional epidermolysis bullosa (EB) mouse model has been used to demonstrate that significant genetic modification of EB symptoms is possible, identifying as modifiers Col17a1 and six other quantitative trait loci, several with strong candidate genes including dystonin (Dst/Bpag1). Here, CRISPR/Cas9 was used to alter exon 23 in mouse skin specific isoform Dst-e (Ensembl GRCm38 transcript name Dst-213, transcript ID ENSMUST00000183302.5, protein size 2639AA) and validate a proposed arginine/glutamine difference at amino acid p1226 in B6 versus 129 mice as a modifier of EB. Frame shift deletions (FSD) in mouse Dst-e exon 23 (Dst-eFSD/FSD) were also identified that cause mice carrying wild-type Lamc2 to develop a phenotype similar to human EB simplex without dystonia musculorum. When combined, Dst-eFSD/FSD modifies Lamc2jeb/jeb (FSD+jeb) induced disease in unexpected ways implicating an altered balance between DST-e (BPAG1e) and a rarely reported rodless DST-eS (BPAG1eS) in epithelium as a possible mechanism. Further, FSD+jeb mice with pinnae removed are found to provide a test bed for studying internal epithelium EB disease and treatment without severe skin disease as a limiting factor while also revealing and accelerating significant nasopharynx symptoms present but not previously noted in Lamc2jeb/jeb mice.

Clinical and molecular features in a cohort of Middle Eastern patients with epidermolysis bullosa.

BACKGROUND: Epidermolysis bullosa (EB) features skin and mucosal fragility due to pathogenic variants in genes encoding components of the cutaneous basement membrane. Based on the level of separation within the dermal-epidermal junction, EB is sub-classified into four major types including EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler EB (KEB) with 16 EB-associated genes reported to date. METHODS: We ascertained a cohort of 151 EB patients of various Middle Eastern ethnic backgrounds. RESULTS: The cohort was comprised of EBS (64%, 97/151), DEB (21%, 31/151), JEB (12%, 18/151), and KEB (3%, 5/151). KRT14 and KRT5 variants were most common among EBS patients with 43% (42/97) and 46% (45/97) of EBS patients carrying mutations in either of these two genes, respectively. Truncal involvement was more common in KRT14-associated EBS as compared to EBS due to KRT5 mutations (p < .05). Mutations in COL17A1 and laminin 332-encoding genes were identified in 55% (10/18) and 45% (8/18) of JEB patients. Scarring alopecia, caries, and EB nevi were most common among JEB patients carrying COL17A1 mutations as compared to laminin 332-associated JEB (p < .05). Abnormal nails were evident in most DEB and JEB patients while poikiloderma was exclusively observed in KEB (p < .001). CONCLUSIONS: EB patients of Middle Eastern origin were found to feature specific phenotype-genotype correlations of relevance to the diagnosis and genetic counseling of patients in this region.

Novel compound heterozygous mutations in the PLEC gene in a neonate with epidermolysis bullosa simplex with pyloric atresia.

Epidermolysis bullosa (EB) is a heterogeneous group of inherited disorders characterized by the blistering of the skin and mucous membranes. Although the molecular basis of EB has been significantly elucidated, the precise phenotypes of the lethal types of EB have not been completely characterized. Herein, we report a severe case of EB with pyloric atresia (PA). The patient was a Japanese boy who not only had skin lesions but also various complications such as PA, dysphagia, hypotonia, infectious keratitis with corneal ulcer, obstructive uropathy and protein-losing enteropathy. Genetic analysis led to the identification of two novel compound heterozygous mutations in the last exon of the plectin (PLEC) gene. Based on this finding, EB simplex with PA was diagnosed. Immunostaining with anti-plectin antibodies revealed truncated plectin proteins lacking the C-terminus in the patient's skin. We also conducted a prenatal diagnosis in subsequent pregnancy. Our report further highlights the crucial role of plectin in many organs and provides valuable information regarding the phenotypes resulting from mutations in the PLEC gene.

Epidemiology of inherited epidermolysis bullosa in Germany.

BACKGROUND: Epidermolysis bullosa (EB) is a rare genetic disorder manifesting with skin and mucosal membrane blistering in different degrees of severity. OBJECTIVE: Epidemiological data from different countries have been published, but none are available from Germany. METHODS: In this population-based cross-sectional study, people living with EB in Germany were identified using the following sources: academic hospitals, diagnostic laboratories and patient organization. RESULTS: Our study indicates an overall EB incidence of 45 per million live births in Germany. With 14.23 per million live births for junctional EB, the incidence is higher than in other countries, possibly reflecting the availability of early molecular genetic diagnostics in severely affected neonates. Dystrophic EB was assessed at 15.58 cases per million live births. The relatively low incidence found for EB simplex, 14.93 per million live births, could be explained by late or missed diagnosis, but also by 33% of cases remaining not otherwise specified. Using log-linear models, we estimated a prevalence of 54 per million for all EB types, 2.44 for junctional EB, 12.16 for dystrophic EB and 28.44 per million for EB simplex. These figures are comparable to previously reported data from other countries. CONCLUSIONS: Altogether, there are at least 2000 patients with EB in the German population. These results should support national policies and pharmaceutical companies in decision-making, allow more precise planning of drug development and clinical trials, and aid patient advocacy groups in their effort to improve quality of life of people with this orphan disease.

Potential di-genic contribution to guttate leukoderma as the predominant feature of epidermolysis bullosa simplex.

Inherited epidermolysis bullosa (EB) simplex is a heterogeneous group of skin fragility disorders caused by mutations in genes encoding cell-cell or cell-matrix adhesion proteins. A recently identified, rare subtype of EB simplex is due to bi-allelic mutations in the EXPH5 gene, which encodes exophilin5, an effector protein of the Rab27B GTPase involved in intracellular vesicle trafficking and exosome secretion. The EXPH5 EB subtype is characterized by early-onset skin blisters and scars, mainly on extremities, and varying degrees of pigmentary alterations. Here, we present a 31-year-old female with diffuse guttate hypopigmentation on the trunk and extremities since early childhood, with no apparent blisters or scars. We employed whole exome sequencing of germline DNA extracted from the patient's leukocytes to determine the genetic aetiology of the phenotype. A novel homozygous variant in EXPH5, c.1153C>T causing a premature stop codon at amino acid Glutamine 385, was identified. Histologic examination after skin pricking disclosed focal keratinocyte detachment typical to EB. Additionally, we identified a deleterious-predicted variant in ENPP1, a gene associated with disturbed transfer of melanosomes to keratinocytes in Cole disease. Our report expands the clinical spectrum of inherited EB simplex with a possible di-genic synergism contributing to co-presentation with guttate leukoderma.

A translation re-initiation variant in KLHL24 also causes epidermolysis bullosa simplex and dilated cardiomyopathy via intermediate filament degradation.

This study shows that gain-of-function variants in KLHL24 causing EBS and DCM, do not only originate in the start-codon and suggest that any nonsense-inducing variant affecting nucleotides c.4_84 will likely cause the same effect on protein level and a similar potential lethal phenotype.

KRT5 missense variant in a Cardigan Welsh Corgi with epidermolysis bullosa simplex.

Epidermolysis bullosa (EB) is a group of blistering disorders that includes several subtypes, classified according to their level of cleavage. Typical clinical signs are blisters and erosions resulting from minimal trauma. The disease has been described in many mammalian species and pathogenic variants in at least 18 different genes have been identified. In the present study, we investigated a Cardigan Welsh Corgi with congenital clinical signs consistent with epidermolysis bullosa. The puppy had blisters and erosions on the paw pads, and the oral mucosa. Histologic examination demonstrated the typical clefting between the dermis and epidermis and confirmed the clinical suspicion. We obtained whole genome sequencing data from the affected puppy and searched for variants in candidate genes known to cause EB. This revealed a heterozygous missense variant, KRT5:p.(E476K), affecting the highly conserved KLLEGE motif of keratin 5. The mutant allele in the affected puppy arose owing to a de novo mutation event as it was absent from both unaffected parents. Knowledge of the functional impact of KRT5 variants in other species together with the demonstration of the de novo mutation event establishes KRT5:p.(E476K) as causative variant for the observed EBS.

Mutation update: The spectra of PLEC sequence variants and related plectinopathies.

Plectin, encoded by PLEC, is a cytoskeletal linker of intermediate filaments expressed in many cell types. Plectin consists of three main domains that determine its functionality: the N-terminal domain, the Rod domain, and the C-terminal domain. Molecular defects of PLEC correlating with the functional aspects lead to a group of rare heritable disorders, plectinopathies. These multisystem disorders include an autosomal dominant form of epidermolysis bullosa simplex (EBS-Ogna), limb-girdle muscular dystrophy (LGMD), aplasia cutis congenita (ACC), and an autosomal recessive form of EBS, which may associate with muscular dystrophy (EBS-MD), pyloric atresia (EBS-PA), and/or congenital myasthenic syndrome (EBS-MyS). In this study, genotyping of over 600 Iranian patients with epidermolysis bullosa by next-generation sequencing identified 15 patients with disease-causing PLEC variants. This mutation update analyzes the clinical spectrum of PLEC in our cohort and in the literature and demonstrates the relationship between PLEC genotype and phenotypic manifestations. This study has integrated our seven novel PLEC variants and phenotypic findings with previously published data totaling 116 variants to provide the most complete overview of pathogenic PLEC variants and related disorders.