Epidermolysis bullosa simplex in Japanese and Korean patients: genetic studies in 19 cases

Signatures of Dermal Fibroblasts from RDEB Pediatric Patients

The recessive form of dystrophic epidermolysis bullosa (RDEB) is a debilitating disease caused by impairments in the junctions of the dermis and the basement membrane of the epidermis. Mutations in the COL7A1 gene induce multiple abnormalities, including chronic inflammation and profibrotic changes in the skin. However, the correlations between the specific mutations in COL7A1 and their phenotypic output remain largely unexplored. The mutations in the COL7A1 gene, described here, were found in the DEB register. Among them, two homozygous mutations and two cases of compound heterozygous mutations were identified. We created the panel of primary patient-specific RDEB fibroblast lines (FEB) and compared it with control fibroblasts from healthy donors (FHC). The set of morphological features and the contraction capacity of the cells distinguished FEB from FHC. We also report the relationships between the mutations and several phenotypic traits of the FEB. Based on the analysis of the available RNA-seq data of RDEB fibroblasts, we performed an RT-qPCR gene expression analysis of our cell lines, confirming the differential status of multiple genes while uncovering the new ones. We anticipate that our panels of cell lines will be useful not only for studying RDEB signatures but also for investigating the overall mechanisms involved in disease progression.

Immunofluorescence mapping, electron microscopy and genetics in the diagnosis and sub-classification of inherited epidermolysis bullosa: a single-centre retrospective comparative study of 87 cases with long-term follow-up

BACKGROUND

Epidermolysis bullosa (EB) comprises a heterogeneous group of skin fragility disorders, classified in four major types based on skin cleavage level, i.e. EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), Kindler EB, and in more than 30 subtypes defined by the combination of laboratory and clinical data, including disease course.

OBJECTIVES

Our aims were to address whether, in the age of genomics, electron microscopy (TEM) has still a role in diagnosing EB, and whether the genotype per se may be sufficient to sub-classify EB.

METHODS

A thoroughly characterized single-centre EB case series was retrospectively evaluated to compare the power of TEM with immunofluorescence mapping (IFM) in establishing the EB type, and the ability of TEM, IFM and genetics to predict selected EB subtypes, i.e. severe dominant EBS (DEBS), severe JEB, severe recessive DEB (RDEB) and DEB self-improving, using genetic and final diagnosis, respectively, as gold standard.

RESULTS

The series consisted of 87 patients, including 44 newborns, with a median follow-up of 54 months. Ninety-five mutations were identified in EB-associated genes, including 25 novel variants. Both IFM and TEM were diagnostic in about all cases of JEB (21/21 for both) and DEB (43/44 for IFM, 44/44 for TEM). TEM sensitivity was superior to IFM for EBS (19/20 vs. 16/19). As to EB subtyping, IFM performed better than genetics in identifying severe JEB cases due to laminin-332 defect (14/14 vs. 10/14) and severe RDEB (eight/nine vs. seven/nine). Genetics had no role in self-improving DEB diagnosis; it almost equalled TEM in predicting severe DEBS (eight/nine vs. nine/nine) and enabled to discriminate dominant from recessive non-severe DEB phenotypes and to identify special subtypes, e.g. DEBS with KLHL24 mutations.

CONCLUSIONS

Transmission electron microscopy remains relevant to the diagnosis of EBS. IFM and genetics are essential and complementary tools in the vast majority of EB cases.

Known and novel mutations responsible for epidermolysis bullosa simplex cases in a Chinese population

Epidermolysis bullosa simplex, generalized severe (EBS-gen sev) is one of the major forms of EBS, caused by mutations of the keratin 5 (KRT5) or keratin 14 (KRT14). However, it is rarely reported in the Chinese population. The current study was performed on three unrelated Chinese families with five patients clinically suspicious for distinct stages of EBS. Mutation screening was performed by direct sequencing of the entire coding regions of KRT5 and KRT14 genes. A diagnosis of EBS-gen sev for patients in these three families was confirmed by revealing missense mutations c.373C>T (p.Arg125Cys), c.374G>T (p.Arg125Leu), and a novel frameshift mutation c.1231delG (p.Glu411Argfs*31) in KRT14. Considering two previously reported cases and the results of the current report, amino acid residue 125 is likely the most frequent hotspot of EBS-gen sev in the Chinese population. The current study further indicated that the symptoms of EBS-gen sev patients decline with age.

Epidermolysis bullosa simplex-generalized severe type due to keratin 5 p.Glu477Lys mutation: Genotype-phenotype correlation and in silico modeling analysis

BACKGROUND/OBJECTIVES

Epidermolysis bullosa is a group of diseases caused by mutations in skin structural proteins. Availability of genetic sequencing makes identification of causative mutations easier, and genotype-phenotype description and correlation are important. We describe six patients with a keratin 5 mutation resulting in a glutamic acid to lysine substitution at position 477 (p.Glu477Lys) who have a distinctive, severe and sometimes fatal phenotype. We also perform in silico modeling to show protein structural changes resulting in instability.

METHODS

In this case series, we collected clinical data from six patients with this mutation identified from their national or local epidermolysis bullosa databases. We performed in silico modeling of the keratin 5-keratin 14 coil 2B complex using CCBuilder and rendered with Pymol (Schrodinger, LLC, New York, NY).

RESULTS

Features include aplasia cutis congenita, generalized blistering, palmoplantar keratoderma, onychodystrophy, airway and developmental abnormalities, and a distinctive reticulated skin pattern. Our in silico model of the keratin 5 p.Glu477Lys mutation predicts conformational change and modification of the surface charge of the keratin heterodimer, severely impairing filament stability.

CONCLUSIONS

Early recognition of the features of this genotype will improve care. In silico analysis of mutated keratin structures provides useful insights into structural instability.

A novel KRT5 mutation associated with generalized severe epidermolysis bullosa simplex in a 2-year-old Chinese boy

Mutations in keratin 5 (KRT5) or KRT14 genes are responsible for the most severe form of epidermolysis bullosa simplex (EBS), which is EBS generalized severe (EBS-gen sev). To date, only four pathogenic mutations (p.Arg165Ser and p.Lys199Asn in KRT5; p.Arg125Cys and p.Arg125His in KRT14) have been reported to be responsible for EBS-gen sev in the Chinese population. In the present study, a 2-year-old Chinese boy was clinically suspected to suffer from EBS, and thus Sanger sequencing was performed in the extracted genomic DNA samples from the patient, his parents and 100 healthy controls. A novel de novo heterozygous missense mutation c.503A>G (p.Glu168Gly) located at the N-terminal end segment of the 1A domain in KRT5 was identified by molecular analysis. In silico analysis tools were used to predict the pathogenicity of the novel missense mutation. A diagnosis of EBS-gen sev was thus confirmed according to the clinical presentations and molecular results.

Novel keratin 5 mutation in a family with epidermolysis bullosa simplex

The aim of the present study was to identify the causative gene defects associated with epidermolysis bullosa simplex (EBS) in a pedigree. The diagnosis of EBS was confirmed in two patients from that pedigree based on the clinical manifestations, histopathological examination of the skin and family history. Blood samples were collected from 6 family members and 100 heathy controls, and genomic DNA and RNA were extracted. Mutation analysis of the keratin 5 gene (KRT5) was conducted using polymerase chain reaction (PCR) direct sequencing and PCR-restriction fragment length polymorphism. In the pedigree, the results of PCR direct sequencing revealed a heterozygous missense mutation in codon 202 of exon 2 of KRT5 (c.605T>A), which led to an amino acid change (p.L202Q) in the patients with EBS but was absent from the unaffected family members and 100 population controls. In conclusion, a novel missense mutation in the KRT5 gene was identified that had a pathogenic role in EBS in the population studied, which enriches the germline mutation spectrum of the KRT5 gene.

Novel sporadic and recurrent mutations in KRT5 and KRT14 genes in Polish epidermolysis bullosa simplex patients: further insights into epidemiology and genotype-phenotype correlation

Epidermolysis bullosa simplex (EBS) is a hereditary genodermatosis characterised by trauma-induced intraepidermal blistering of the skin. EBS is mostly caused by mutations in the KRT5 and KRT14 genes. Disease severity partially depends on the affected keratin type and may be modulated by mutation type and location. The aim of our study was to identify the molecular defects in KRT5 and KRT14 in a cohort of 46 Polish and one Belarusian probands with clinical suspicion of EBS and to determine the genotype-phenotype correlation. The group of 47 patients with clinical recognition of EBS was enrolled in the study. We analysed all coding exons of KRT5 and KRT14 using Sanger sequencing. The pathogenic status of novel variants was evaluated using bioinformatical tools, control group analysis (DNA from 100 healthy population-matched subjects) and probands' parents testing. We identified mutations in 80 % of patients and found 29 different mutations, 11 of which were novel and six were found in more than one family. All novel mutations were ascertained as pathogenic. In the majority of cases, the most severe genotype was associated with mutations in highly conserved regions. In some cases, different inheritance mode and clinical significance, than previously reported by others, was observed. We report 11 novel variants and show novel genotype-phenotype correlations. Our data give further insight into the natural history of EBS molecular pathology, epidemiology and mutation origin.

Weber-Cockayne Type Epidermolysis Bullosa Simplex Resulting from a Novel Mutation (c. 608T>C) in the Keratin 5 Gene

Epidermolysis bullosa simplex (EBS), an inherited genetic disorder, is most often caused by a dominant-negative mutation in either the keratin 5 (KRT5) or the keratin 14 (KRT14) gene. These keratin mutants result in a weakened cytoskeleton and cause extensive cytolysis. It is important to analyze the KRT5 or KRT14 genes of the patient and their family members by mutational analysis in order to identify genetic defects as well as the need for genetic counseling. In this study, we present a 5-year-old Korean boy who had been developing blisters and erosions on the palms of his hands and soles of his feet since infancy. In addition, while his younger sister and father showed similar clinical manifestation, his mother did not. The patient was diagnosed with EBS based on clinical manifestation, which is characterized by the presence of blisters restricted to the palms and soles, histological findings, and mutational analysis. Mutational analysis of the patient's DNA revealed a thymine-to-cytosine transition at codon 608 in the KRT-5 gene, resulting in a leucine-to-proline substitution in the keratin 5 protein. The same mutation was identified in the paternal, but not maternal, DNA. Here, we report a case of Weber-Cockayne type EBS with vesicles and bullae restricted to the palms and soles with a novel, paternally inherited mutation in KRT5 gene (exon2, c.608T>C).

Verrucous carcinoma in epidermolysis bullosa simplex is possibly associated with a novel mutation in the keratin 5 gene

Epidermolysis bullosa simplex (EBS) is mainly caused by mutations in the KRT5 and KRT14 genes. Squamous cell carcinoma (SCC) represents the second most frequent skin neoplasia with complex aetiology. The molecular events disrupting the orchestrated interplay between the cytoskeleton, cell adhesion molecules and signalling proteins are ill understood in SCC. We describe the molecular background and the unusual course of the disease in a patient with EBS Dowling-Meara, severe keratoderma and a massive verrucous carcinoma. Skin and tumour samples from the patient were analysed using light microscopy, immunohistochemistry and immunofluorescence mapping. Mutation analysis of the KRT5 and KRT14 genes identified the novel KRT5 mutation p.E477D. Invasive tumour areas were characterized by downregulation of keratins 5 and 14, reduced and irregular desmocollin-2 expression and increased expression of keratins 6, 16 and 17. Levels of Ki-67 were increased and levels of E-cadherin strongly reduced in the tumour tissue. In this case a novel KRT5 mutation led to increased fragility of keratinocytes. Desmosome and adherens junctions were destabilized, which may trigger keratinocyte-mediated inflammation, possibly via p120-catenin-dependent signalling, suggesting a link between a keratin mutation and SCC, which adds weight to the hypothesis that disturbance of the cytoskeleton represents a major cause in the appearance of the malignant phenotype. Some individuals with EBS may be at risk of developing secondary SCC.

Two novel recessive mutations in KRT14 identified in a cohort of 21 Spanish families with epidermolysis bullosa simplex

BACKGROUND

Basal epidermolysis bullosa simplex (EBS) is a group of blistering genodermatoses mostly caused by mutations in the keratin genes, KRT5 and KRT14. Recessive mutations represent about 5% of all EBS mutations, being common and specific in populations with high consanguinity, where affected patients show severe phenotypes.

OBJECTIVES

To accomplish the first mutational analysis in patients of Spanish origin with EBS and to delineate a comprehensive genotype-phenotype correlation.

METHODS

Twenty-one EBS families were analysed. Immunofluorescence mapping at the dermoepidermal junction level was performed on skin biopsies from patients. Mutation screening of the entire coding sequences of KRT5 and KRT14 in genomic DNA was assessed by polymerase chain reaction and direct sequencing.

RESULTS

KRT5 or KRT14 causative mutations were identified in 18 of the 21 EBS families. A total of 14 different mutations were disclosed, of which 12 were dominant missense mutations and two truncating recessive mutations. Five of the 14 mutations were novel including three dominant in KRT5 (p.V186E, p.T321P and p.A428T) and two recessive in KRT14 (p.K116X and p.K250RfsX8). The two patients with EBS carrying homozygous recessive mutations were affected by severe phenotypes and belonged to consanguineous families. All five families with the EBS Dowling-Meara subtype carried recurrent mutations affecting the highly conserved ends of the α-helical rod domain of K5 and K14. The seven mutations associated with the localized EBS subtype were widely distributed along the KRT5 and KRT14 genes. Two families with mottled pigmentation carried the P25L mutation in KRT5, commonly associated with this subtype.

CONCLUSIONS

This study further confirms the genotype-phenotype correlation established for EBS in other ethnic groups, and is the first in a Mediterranean country (excluding Israel). This study adds two novel recessive mutations to the worldwide record to date, which includes a total of 14 mutations. As in previous reports, the recessive mutations resulted in a lack of keratin K14, giving rise to a generalized and severe presentation.

Consequences of two different amino-acid substitutions at the same codon in KRT14 indicate definitive roles of structural distortion in epidermolysis bullosa simplex pathogenesis

Numerous inherited diseases develop due to missense mutations, leading to an amino-acid substitution. Whether an amino-acid change is pathogenic depends on the level of deleterious effects caused by the amino-acid alteration. We show an example of different structural and phenotypic consequences caused by two individual amino-acid changes at the same position. Epidermolysis bullosa simplex (EBS) is a genodermatosis resulting from KRT5 or KRT14 mutations. Mutation analysis of an EBS family revealed that affected individuals were heterozygous for a, to our knowledge, previously unreported mutation of c.1237G>C (p.Ala413Pro) in KRT14. Interestingly, 2 of 100 unrelated normal controls were heterozygous, and 1 of the 100 was homozygous for a different mutation in this position, c.1237G>A (p.Ala413Thr). In silico modeling of the protein demonstrated deleterious structural effects from proline substitution but not from threonine substitution. In vitro transfection studies revealed a significantly larger number of keratin-clumped cells in HaCaT cells transfected with mutant KRT14 complementary DNA (cDNA) harboring p.Ala413Pro than those transfected with wild-type KRT14 cDNA or mutant KRT14 cDNA harboring p.Ala413Thr. These results show that changes in two distinct amino acids at a locus are destined to elicit different phenotypes due to the degree of structural distortion resulting from the amino-acid alterations.

Mutations in KRT5 and KRT14 cause epidermolysis bullosa simplex in 75% of the patients

BACKGROUND

Epidermolysis bullosa simplex (EBS) is a mechanobullous genodermatosis that may be caused by mutations in the genes KRT5 and KRT14 encoding the basal epidermal keratins 5 (K5) and 14 (K14). Three main clinical subtypes of EBS exist, differing in onset, distribution and severity of skin blistering. Previous reports of KRT5 and KRT14 mutations suggest a correlation between the location of the mutation and the severity of the associated EBS phenotype.

OBJECTIVES

The prevalence of KRT5/KRT14 mutations and the genotype-phenotype correlation in the largest tissue-confirmed EBS population is investigated.

METHODS

KRT5 and KRT14 genomic DNA and cDNA sequences of 76 clinically well-defined unrelated EBS probands were amplified and then subjected to direct sequencing and product length analysis. Immunofluorescence microscopy on patients' skin biopsies with antibodies against K5 and K14 was performed to study protein expression.

RESULTS

In 57 of 76 (75%) probands 41 different KRT5 and KRT14 mutations were identified, of which 12 were novel. Mutations affecting the highly conserved helix boundary motifs of the rod domains of K5 and K14, and the K14 helix initiation motif in particular, were associated with the severest, EBS Dowling-Meara, phenotype. In 21 EBS probands (37%) the mutation was de novo. In 19 probands (25%) KRT5 or KRT14 mutations were excluded.

CONCLUSIONS

The phenotype-genotype correlation observed in this large EBS population underscores the importance of helix boundary motifs for keratin assembly. Only three-quarters of biopsy-confirmed EBS probands have KRT5 or KRT14 mutations, indicating genetic heterogeneity in EBS. Alternative gene candidates are discussed.

A transient epidermolysis bullosa simplex-like phenotype associated with bexarotene treatment in a G138E KRT5 heterozygote

Basal keratinocyte lysis is the hallmark histopathological finding of epidermolysis bullosa simplex (EBS), a group of rare heritable mechanobullous disorders characterized by intraepidermal blister formation and skin fragility. Over 100 mutations, found predominantly in the genes encoding keratins 5 and 14 (KRT5, KRT14), have been described to account for a variety of clinical subtypes. EBS with mottled pigmentation (EBS-MP) is a rare variant featuring childhood-onset reticulate hyperpigmentation and focal palmoplantar keratoderma, typically associated with a P25L KRT5 mutation. In this report, we present the case of a 77-year-old woman with a history of palmoplantar keratoderma who developed a transient EBS-MP-like phenotype associated with bexarotene treatment for cutaneous T-cell lymphoma. Genetic sequencing revealed a heterozygous G138E KRT5 variant, present in approximately 10% of the European population and only rarely associated with pathology. Bexarotene, which has been reported to alter keratin synthesis, caused vesiculobullous reactions with similar frequency in clinical trials. We propose that the cumulative effect of drug treatment and underlying G138E polymorphism resulted in transient basal keratinocyte lysis in our patient and provides a plausible explanation for this unusual bexarotene side effect.

Epidermolysis bullosa in Japan

Epidermolysis bullosa (EB) is a group of hereditary disorders characterized by mechanical stress-induced blistering of the skin and mucous membranes. This article discusses the prevalence among and genetic studies of Japanese patients with EB.

One novel and two recurrent mutations in the keratin 5 gene identified in Chinese patients with epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited skin diseases, characterized by the formation of intraepidermal blisters. We performed genetic analysis of the keratin 5 (KRT5) gene in two Chinese pedigrees. One novel missense mutation was identified in a patient with sporadic EBS (general, non-Dowling-Meara). Sequence analysis showed a heterozygous T > A transition at nucleotide 1730 of KRT5, changing phenylalanine (Phe) to tyrosine (Tyr) at position 577 of the keratin 5 (K5). In addition, two recurrent mutations c.1649delG (p.Gly550AlafsX77) and c.508G > (p.Glu170Lys) in KRT5 were identified in Chinese patients with mottled pigmentation EBS and localized EBS, respectively. None of the mutations were found in any unaffected family members or in an additional 100 unrelated control samples. These results suggest that these mutations are pathogenic and might be one of the potential causes of EBS in these Chinese patients.