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

A Novel Mutation p.L461P in KRT5 Causing Localized Epidermolysis Bullosa Simplex

Background

Epidermolysis bullosa (EB) is a rare genetic disease with widely different clinical manifestations, but the relationship between genotype and phenotype is not fully understood. In the present study, we recruited a Chinese family in which two members had been diagnosed with localized EB simplex (EBS), with clinical manifestation, including blisters and erosions on the soles of the feet since infancy.

Objective

To identify and confirm the genetic variation in a Chinese family diagnosed as localized EBS.

Methods

Our study included two patients, other healthy members of the family, and 100 normal controls. Genomic DNA samples were isolated from each participant, and then polymerase chain reaction (PCR) direct sequencing was performed.

Results

The results of PCR direct sequencing revealed a novel heterozygous missense mutation in codon 461 of exon 7 of KRT5 (c.1382T>C), which led to an amino acid change (p.L461P) in the patients with EBS but was absent in unaffected family members and 100 unrelated control samples.

Conclusion

The present study broadens the mutational spectrum of EBS, and this knowledge could be harnessed for prenatal screening, gene diagnosis, and gene therapy for localized EBS.

Molecular Modeling of Pathogenic Mutations in the Keratin 1B Domain

Keratin intermediate filaments constitute the primary cytoskeletal component of epithelial cells. Numerous human disease phenotypes related to keratin mutation remain mechanistically elusive. Our recent crystal structures of the helix 1B heterotetramer from keratin 1/10 enabled further investigation of the effect of pathologic 1B domain mutations on keratin structure. We used our highest resolution keratin 1B structure as a template for homology-modeling the 1B heterotetramers of keratin 5/14 (associated with blistering skin disorders), keratin 8/18 (associated with liver disease), and keratin 74/28 (associated with hair disorder). Each structure was examined for the molecular alterations caused by incorporating pathogenic 1B keratin mutations. Structural modeling indicated keratin 1B mutations can harm the heterodimer interface (R265P^K5, L311R^K5, R211P^K14, I150V^K18), the tetramer interface (F231L^K1, F274S^K74), or higher-order interactions needed for mature filament formation (S233L^K1, L311R^K5, Q169E^K8, H128L^K18). The biochemical changes included altered hydrophobic and electrostatic interactions, and altered surface charge, hydrophobicity or contour. Together, these findings advance the genotype-structurotype-phenotype correlation for keratin-based human diseases.

Analysis of KRT5 and KRT14 gene mutations and mode of inheritance in Iranian patients with clinical suspicion of Epidermolysis bullosa simplex

Background: Epidermolysis bullosa simplex is a hereditary skin disorder caused by mutations in several genes such as KRT5 and KRT14 . Skin fragility in basal keratinocytes presence regions led to the cytolysis of epidermis and blistering. Aim of this study was to detect the molecular defects in KRT5 and KRT14 genes hot spots in patients with clinical suspicion of EBS and investigation of their probable genotype-phenotype correlations.

Methods: Exons 1 and 6-7 of KRT5 and exons 1 and 4-7 of KRT14 amplification and mutation detection were performed by polymerase chain reaction and Sanger sequencing, respectively. Novel variants pathogenicity evaluated by bioinformatics tools.

Results: Nine important variants detected in seven different patients within 6 Iranian families affected by Epidermolysis bullosa simplex, of which four variants were novel. Three patients had a mottled pigmentation phenotype [G96D (p.Gly96Asp) and F97I (p.Phe97Ile) in KRT5 ]. One of them showed a Dowling–Meara phenotype [A417P (p.Ala417Pro) and E477D (p.Glu477Asp) in KRT5 ] and another had a Koebner type phenotype [R397I (p.Arg397Ile) and Q444* (p.Gln444Ter) in KRT5 ]. A novel variant [G92E (p.Gly92Glu) in KRT5 ] in a double heterozygous state with a challenging variant [A413T (p.Ala413Thr) in KRT14 ] identified in one patient with Koebner type phenotype. Also, a previously reported mutation [I377T (p.Ile377Thr) in KRT14 gene] identified in this study.

Conclusion: The results of molecular data analysis showed that the most severe phenotypes were associated with mutations in highly conserved regions. In some cases, different inheritance modes were observed.

Genotype-phenotype correlations on epidermolysis bullosa with congenital absence of skin: A comprehensive review

Congenital absence of skin (CAS) is a clinical sign associated with the main types of epidermolysis bullosa (EB). Very few studies have investigated the genetic background that may influence the occurrence of this condition. Our objective was to investigate genotype-phenotype correlations on EB with CAS through a literature revision on the pathogenic variants previously reported. A total of 171 cases (49 EB simplex, EBS; 23 junctional EB, JEB; and 99 dystrophic EB, DEB), associated with 132 pathogenic variants in eight genes, were included in the genotype-phenotype analysis. In EBS, CAS showed to be a recurrent clinical sign in EBS with pyloric atresia (PA) and EBS associated with kelch-like protein 24; CAS was also described in patients with keratins 5/14 alterations, particularly involving severe phenotypes. In JEB, this is a common clinical sign in JEB with PA associated with premature termination codon variants and/or amino acid substitutions located in the extracellular domain of integrin α6β4 genes. In DEB with CAS, missense variants occurring close to non-collagenous interruptions of the triple-helix domain of collagen VII appear to influence this condition. This study is the largest review of patients with EB and CAS and expands the spectrum of known variants on this phenomenon.

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.

Epidermal keratin 5 expression and distribution is under dermal influence

Human skin melanin pigmentation is regulated by systemic and local factors. According to the type of melanin produced by melanocytes, the transfer and degradation of melanosomes differ, thus accounting for most variations between ethnicities. We made the surprising observation that in a drastically changed environment, white and black phenotypes are reversible since Caucasian skin grafted onto nude mice can become black with all black phenotypic characteristics. Black xenografts differed essentially from other grafts by the levels of epidermal FGF-2 and keratin 5. In vitro analysis confirmed that FGF-2 directly regulates keratin 5. Interestingly, this phenomenon may be involved in human pathology. Keratin 5 mutations in Dowling-Degos Disease (DDD) have already been associated with the pheomelanosome-eumelanosome transition. In a DDD patient, keratin 5 was expressed in the basal and spinous layers, as observed in black xenografts. Furthermore, in a common age-related hyperpigmentation disorder like senile lentigo (SL), keratin 5 distribution is also altered. In conclusion, modulation of keratin 5 expression and distribution either due to mutations or factors may account for the development of pigmentary disorders.

A novel de novo mutation p.Ala428Asp in KRT5 gene as a cause of localized epidermolysis bullosa simplex

Epidermolysis bullosa is a group of inherited blistering skin diseases resulting in most cases from missense mutations in KRT5 and KRT14 genes encoding the basal epidermal keratins 5 and 14. Here, we present a patient diagnosed with a localized subtype of epidermolysis bullosa simplex caused by a heterozygous mutation p.Ala428Asp in the KRT5 gene, that has not been previously identified. Moreover, a bioinformatic analysis of the novel mutation was performed, showing changes in the interaction network between the proteins. Identification of novel mutations and genotype-phenotype correlations allow to better understanding of underlying pathophysiologic bases and is important for genetic counselling, patients' management, and disease course prediction.

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.

Genetic diagnosis of epidermolysis bullosa: recommendations from an expert Spanish research group

Epidermolysis bullosa (EB) is a rare genetic disease that causes mucocutaneous fragility. It comprises a clinically and genetically heterogeneous group of disorder characterized by spontaneous or contact/friction-induced blistering. EB is classified into 4 types-simplex, junctional, dystrophic, and Kindler syndrome-and 30 subtypes. The disease is caused by defects in proteins implicated in dermal-epidermal adhesion. At least 19 genes have been characterized and more than 1000 mutations identified, thus rendering diagnosis complex. Molecular diagnosis of EB is the last stage of a laborious process that starts with a detailed clinical history compilation and careful procurement of a skin fresh biopsy that includes an area where the epidermis detaches from the dermis. The detachment area makes it possible to establish the cleavage plane by antigen mapping and, in the best scenario, to identify a single candidate gene to search for pathogenic mutations. The results of the molecular diagnosis enable the physician to provide appropriate genetic counseling (inheritance pattern, risk of recurrence, and options for prenatal and preimplantation diagnosis) and implement subsequent preventive programs, as well as to establish a reasonable clinical prognosis facilitating access to specific therapy and rehabilitation. Lastly, molecular diagnosis is essential for the participation of patients in clinical trials, a critical issue given the current incurable status of EB. The present guidelines aim to disseminate the procedure for diagnosing EB in our laboratory and thus avoid suboptimal or incomplete clinical diagnoses. The recommendations we provide are the result of more than 10 years' experience in the molecular diagnosis of EB in Spain.

Mutations Affecting Keratin 10 Surface-Exposed Residues Highlight the Structural Basis of Phenotypic Variation in Epidermolytic Ichthyosis

Epidermolytic ichthyosis (EI) due to KRT10 mutations is a rare, typically autosomal dominant, disorder characterized by generalized erythema and cutaneous blistering at birth followed by hyperkeratosis and less frequent blistering later in life. We identified two KRT10 mutations p.Q434del and p.R441P in subjects presenting with a mild EI phenotype. Both occur within the mutational "hot spot" of the keratin 10 (K10) 2B rod domain, adjacent to severe EI-associated mutations. p.Q434del and p.R441P formed collapsed K10 fibers rather than aggregates characteristic of severe EI KRT10 mutations such as p.R156C. Upon differentiation, keratinocytes from p.Q434del showed significantly lower apoptosis (P-value<0.01) compared with p.R156C as assessed by the TUNEL assay. Conversely, the mitotic index of the p.Q434del epidermis was significantly higher compared with that of p.R156C (P-value<0.01) as estimated by the Ki67 assay. Structural basis of EI phenotype variation was investigated by homology-based modeling of wild-type and mutant K1-K10 dimers. Both mild EI mutations were found to affect the surface-exposed residues of the K10 alpha helix coiled-coil and caused localized disorganization of the K1-K10 heterodimer. In contrast, adjacent severe EI mutations disrupt key intermolecular dimer interactions. Our findings provide structural insights into phenotypic variation in EI due to KRT10 mutations.

Epidermolysis bullosa simplex with mottled pigmentation: a family report and review

Epidermolysis bullosa simplex with mottled hyperpigmentation (EBS-MP) is an uncommon subtype of EBS. Its clinical features depend on the age of diagnosis, and clinical variations have been described even within family members. We present six cases from two unrelated Spanish families each with several affected members with EBS-MP and review the clinical and genetic findings in all reported patients. We highlight the changing clinical features of the disease throughout life.