KRT5 Mutations Research Articles

Epidermolysis bullosa simplex due toKRT5mutations: mutation-related differences in cellular fragility and the protective effects of trimethylamineN-oxide in cultured primary keratinocytes

Epidermolysis bullosa simplex (EBS) is a mechanobullous skin fragility disease characterized by cytolysis of basal keratinocytes and intraepidermal blistering often caused by mutations in keratin genes (KRT5 or KRT14). No remedies exist for these disorders presenting a need for development of novel therapies. To identify new genotype-phenotype relationships in vivo and in cultured primary EBS keratinocytes in vitro, and to study the cytoskeletal stabilizing effects of trimethylamine N-oxide (TMAO) in heat-stressed EBS cells. Genomic DNA and cDNA samples from three Swedish patients with EBS were analysed for keratin mutations. Primary EBS keratinocyte cultures were established, heat stressed with and without added TMAO, followed by evaluation of cellular fragility. In addition to the previously reported KRT5 mutation (V186L) in one patient, two patients were found to have a novel I183M and recurrent E475G replacements in KRT5. Cultured EBS keratinocytes did not exhibit keratin aggregates or cell loss, except in the patient with the p.I183M mutation who showed 3% aggregates and 2% cell loss. Upon transient heat stress the number of aggregate-containing cells increased to 21%, 27% and 13%, respectively, in the p.I183M, p.E475G and p.V186L mutant cells. Interestingly, pretreatment with TMAO prior to heat stress, dose dependently reduced the number of aggregate-containing cells and cell loss. These results revealed a genotype-phenotype correlation in EBS keratinocytes upon heat stress and suggest protein stabilization as a new therapeutic strategy.

Epidermolysis Bullosa Simplex

The prevalence of epidermolysis bullosa simplex (EBS) is estimated to be approximately 6 to 30 per 1 million live births. The disease is usually caused by missense mutations in KRT5 and KRT14, encoding keratins mostly expressed in the epidermal basal layer. Major advances in understanding of the molecular basis of EBS and other keratin disorders have led to the development of DNA-based prenatal testing.

Disadhesion of epidermal keratinocytes: A histologic clue to palmoplantar keratodermas caused by DSG1 mutations

Recent developments in molecular genetics may lead to re-examination of the histopathology of inherited palmoplantar keratodermas (PPKs) based on more precise groupings of the various entities and syndromes. We sought to characterize the histopathological findings in PPKs associated with mutations in DSG1, which encodes desmoglein 1. We studied the histopathology of 3 cases of keratosis palmoplantaris striata type I and one case of diffuse PPK, all associated with autosomal-dominant mutations in DSG1. Our cases for comparison included 4 cases with Mal de Meleda PPK associated with autosomal-recessive SLURP1 mutations, one case with pachyonychia congenita type II PPK associated with an autosomal-dominant KRT17 mutation, and one case with focal PPK associated with an autosomal-dominant KRT16 mutation. The distinguishing histopathological features of the 3 keratosis palmoplantaris striata type I cases and the diffuse PPK case associated with DSG1 mutation were: varying degrees of widening of the intercellular spaces and partial disadhesion of keratinocytes in the mid and upper epidermal spinous cell layers, often extending to the granular cell layer. These findings, which are associated with haploinsufficiency of desmoglein 1, were not observed in any of the other 6 PPK cases. Mild perinuclear eosinophilic condensations and cytoplasmic vacuolizations were observed in the spinous cell layer keratinocytes of the pachyonychia congenita type II PPK and the nonspecified focal PPK cases. There were a limited number of patients and control patients with hereditary PPKs. Widening of the intercellular spaces and disadhesion of epidermal keratinocytes may serve as a histologic clue to PPKs caused by DSG1 mutations.

Increased pachyonychia congenita severity in patients with concurrent keratin and filaggrin mutations

Pachyonychia congenita (PC), a rare autosomal-dominant keratin disorder caused by mutations in keratin genes KRT6A/B, KRT16 or KRT17, is characterized by painful plantar keratoderma and hypertrophic nail dystrophy. Loss-of-function mutations in the filaggrin (FLG) gene underlie the most prevalent skin disorder of cornification, ichthyosis vulgaris (IV), which presents with generalized scaling and is also associated with atopic dermatitis. Recently, FLG mutations have been reported to increase phenotype severity of X-linked ichthyosis and alopecia areata. We report a parent-child trio in which the mother and the son have PC and the father has IV. Both the mother and the son are carriers for the KRT16 mutation p.Leu132Pro. The son, who is much more severely affected than his mother, in addition carries the heterozygous FLG mutation p.R2447X, which was inherited from the father. This observation suggests that coinheritance of mutations in KRT16 and FLG may aggravate the PC phenotype and that FLG could serve as a genetic modifier in PC.

Cytokines as genetic modifiers in K5���/���mice and in human epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is a skin disorder caused by fully-penetrant mutations in the keratin genes KRT5 and KRT14, leading to extensive cytolysis and cell fragility of basal keratinocytes. EBS is subject to environmental conditions and displays high intra- and interfamilial variability, suggesting modifying loci. Here, we demonstrate that upregulation of certain cytokines accompanies mutations in keratin 5 (K5) but not in keratin 14 (K14). We find for the first time that cytokines macrophage chemotactic protein (MCP)-1/[chemokine (C-C motif) ligand 2] (CCL2), macrophage inflammatory protein (MIP)-3beta/CCL19 and MIP-3alpha/CCL20, all regulated by nuclear factor kappa B (NFkappaB) and involved in the recruitment, maturation, and migration of Langerhans cells (LCs) in the epidermis, are upregulated in the skin of K5(-/-), but not of K14(-/-) mice. In neonatal K5(-/-) epidermis, the number of LCs was increased two-fold. At the same time, tumor necrosis factor alpha (TNFalpha) remained unaltered, demonstrating the specificity of that process. Most remarkably, enhanced LC recruitment within the epidermis was found in five EBS patients carrying mutations in the KRT5 gene but not in EBS patients with KRT14 gene mutations. In agreement with the NFkappaB-dependent regulation of these cytokines, we found a decrease in p120-catenin in the basal epidermis of K5(-/-) mice. These data provide the first explanation for distinct, keratin-type-specific genotype-phenotype correlations in EBS and represent a rationale to investigate gene loci affecting skin pathology in EBS.

Dyskeratosis as a histologic feature in epidermolysis bullosa simplex-Dowling Meara

Intracellular keratin aggregation and clumping is a characteristic ultrastructural feature in epidermolysis bullosa simplex (EBS)-Dowling Meara (DM) yet without histologic correlates in routinely stained specimens. We sought to detect histologic clues to keratin aggregation and clumping in the involved epidermis of EBS-DM. Four cases of EBS-DM caused by dominant keratin (KRT)5 and KRT14 mutations were studied histologically and ultrastructurally. The histologic slides of 11 additional EBS cases (9 Weber-Cockayne subtypes and two Koebner subtypes) were also reviewed histologically. Intracytoplasmic aggregation and clumping of tonofilaments were observed ultrastructurally in all 4 EBS-DM cases. Intracytoplasmic eosinophilic homogenizations and inclusions (ie, dyskeratosis) in individual keratinocytes were detected histologically in 3 of the 4 EBS-DM cases, but in none of the 9 EBS-Weber-Cockayne cases or the two EBS-Koebner cases. This was a relatively small studied group. The histopathological detection of dyskeratosis in individual keratinocytes may provide a valuable clue to keratin aggregation and clumping, and to the diagnosis in EBS-DM.

Naegeli-Franceschetti-Jadassohn Syndrome and Dermatopathia Pigmentosa Reticularis: Two Allelic Ectodermal Dysplasias Caused by Dominant Mutations in KRT14

Naegeli-Franceschetti-Jadassohn syndrome (NFJS) and dermatopathia pigmentosa reticularis (DPR) are two closely related autosomal dominant ectodermal dysplasia syndromes that clinically share complete absence of dermatoglyphics (fingerprint lines), a reticulate pattern of skin hyperpigmentation, thickening of the palms and soles (palmoplantar keratoderma), abnormal sweating, and other subtle developmental anomalies of the teeth, hair, and skin. To decipher the molecular basis of these disorders, we studied one family with DPR and four families with NFJS. We initially reassessed linkage of NFJS/DPR to a previously established locus on 17q11.2-q21. Combined multipoint analysis generated a maximal LOD score of 8.3 at marker D17S800 at a recombination fraction of 0. The disease interval was found to harbor 230 genes, including a large cluster of keratin genes. Heterozygous nonsense or frameshift mutations in KRT14 were found to segregate with the disease trait in all five families. In contrast with KRT14 mutations affecting the central alpha -helical rod domain of keratin 14, which are known to cause epidermolysis bullosa simplex, NFJS/DPR-associated mutations were found in a region of the gene encoding the nonhelical head (E1/V1) domain and are predicted to result in very early termination of translation. These data suggest that KRT14 plays an important role during ontogenesis of dermatoglyphics and sweat glands. Among other functions, the N-terminal part of keratin molecules has been shown to confer protection against proapoptotic signals. Ultrastructural examination of patient skin biopsy specimens provided evidence for increased apoptotic activity in the basal cell layer where KRT14 is expressed, suggesting that apoptosis is an important mechanism in the pathogenesis of NFJS/DPR.

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

Epidermolysis bullosa simplex (EBS) comprises a group of hereditary bullous diseases characterized by intraepidermal blistering caused by mutations in either keratin gene, KRT5 or KRT14. Significant correlation between the position of mutations within these proteins and the clinical severity of EBS has been noted. A recent report showed EBS cases in Israel had unique genetic features compared with European or U.S.A. associated families, which suggests that the ethnic and geographical features of EBS patients may be different. To assess the possibility that EBS may present with certain specific features in Japanese and Koreans and to identify additional EBS mutations for genotype/phenotype correlation. EBS was clinically diagnosed and confirmed by transmission electron microscopic examination of a skin biopsy. Mutation analysis of KRT5 and KRT14 was performed by direct sequencing in 17 Japanese and two Korean EBS patients. We have identified six novel KRT5 missense mutations (V143D, D158V, V186M, Q191P, R352S, G517D). R352S is the first mutation in the 2A domain. Most of these novel mutations changed amino acids that were evolutionarily conserved. Eight including all five mutations in EBS-Dowling-Meara patients have been previously reported. We were unable to detect mutations in five sporadic EBS-Koebner patients. The proportion of mutations in KRT5 (11 of 14; 78%) is higher than that for KRT14 mutations (3 of 14; 21%) in these Japanese and Korean EBS patients. Japanese and Korean patients with EBS showed very similar phenotype and genotype correlations with patients from Western countries. Whether the higher proportion of KRT5 mutations is a definite characteristic of Japanese and Korean patients with EBS or not, requires further research into mutations in Japanese and Korean people.

Three Severe Cases of EBS Dowling-Meara Caused by Missense and Frameshift Mutations in the Keratin 14 Gene

We report three unrelated patients affected at birth with an unusually severe form of epidermolysis bullosa simplex Dowling-Meara type (EBS-DM) because of mutations in KRT14 encoding keratin 14. Two patients were heterozygous for the previously described p.M119T mutation. The third patient was heterozygous for a novel c.1246delC mutation predicting the replacement of the helix termination peptide and the tail domain by a 25 amino-acid aberrant carboxyterminal sequence. At age 2 years, patients carrying the p.M119T mutation still suffered from severe EBS-DM, whereas the patient harboring the c.1246delC mutation has improved over time. These cases illustrate genotype-phenotype correlations and have implications for genetic counselling of EBS.

A human keratin 10 knockout causes recessive epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis (EHK) is a blistering skin disease inherited as an autosomal-dominant trait. The disease is caused by genetic defects of the epidermal keratin K1 or K10, leading to an impaired tonofilament network of differentiating epidermal cells. Here, we describe for the first time a kindred with recessive inheritance of EHK. Sequence analysis revealed a homozygous nonsense mutation of the KRT10 gene in the affected family members, leading to a premature termination codon (p.Q434X), whereas the clinically unaffected consanguineous parents were both heterozygous carriers of the mutation. Semi-quantitative RT-PCR and western blot analysis demonstrated degradation of the KRT10 transcript, resulting in complete absence of keratin K10 protein in the epidermis and cultured keratinocytes of homozygous patients. This K10 null mutation leads to a severe phenotype, clinically resembling autosomal-dominant EHK, but differing in form and distribution of keratin aggregates on ultrastructural analysis. Strong induction of the wound-healing keratins K6, K16 and K17 was found in the suprabasal epidermis, which are not able to compensate for the lack of keratin 10. We demonstrate that a recessive mutation in KRT10 leading to a complete human K10 knockout can cause EHK. Identification of the heterogeneity of this disorder has a major impact for the accurate genetic counseling of patients and their families and also has implications for gene-therapy approaches.

Epidermolysis Bullosa Simplex: Recurrent and De Novo Mutations in the KRT5 and KRT14 Genes, Phenotype/Genotype Correlations, and Implications for Genetic Counseling and Prenatal Diagnosis

Epidermolysis bullosa simplex (EBS) is a mechano-bullous disorder characterized by intraepidermal blistering within the basal keratinocytes as a result of trauma to the skin. As part of the DNA diagnostics program, our laboratory has analyzed a cohort of 57 patients with the initial referral diagnosis of EBS. Among these patients, 18 were found to harbor heterozygous mutations in the keratin 5 or keratin 14 genes, KRT5 and KRT14, respectively, whereas in 14 cases, the disease was associated with mutations in both alleles of the plectin gene. Among the keratin mutations, 12 were distinct and six were novel, and in most cases there was no family history of a blistering disease. Prenatal diagnosis of eight pregnancies with keratin gene mutations, at risk for EBS either because one of the parents was affected (three cases) or history of a previously affected child as a result of a de novo mutation (five cases), predicted two fetuses being affected and six being normal. No recurrence of the de novo mutations in these pregnancies was disclosed. Collectively, the data suggest that a significant number of cases diagnosed as EBS are due to plectin mutations, and many cases result from de novo mutations in KRT5 and KRT14 genes. These findings have implications for genetic counseling and prenatal diagnosis for EBS.

Mutation analysis of the entire keratin 5 and 14 genes in patients with epidermolysis bullosa simplex and identification of novel mutations

Epidermolysis bullosa simplex is a group of blistering skin disorders caused by defects in one of the keratin genes, KRT5 and KRT14. Previously reported KRT5 and KRT14 mutations are clustered in several hotspots, namely the rod ends of the 1A and 2B domains and in the non-helical linker region L12. Therefore, genomic KRT5 and KRT14 mutation analysis was initially limited to these hotspots. In this study we describe the screening of nine EBS patients for mutations in the hotspots. In two patients, with the Koebner and the Weber-Cockayne subtypes of epidermolysis bullosa simplex respectively, we could, however, not identify any mutation in one of the hotspot domains of KRT5 and KRT14. Therefore, it appeared to be necessary to screen the entire genes for mutations. For KRT5, a complete genomic mutation detection system was previously described. We now developed a complete genomic mutation detection system for KRT14. For the amplification of the KRT14 genes, we make use of restriction sites to exempt the keratin 14 pseudogene sequence from polymerase chain reaction amplification. Using the complete genomic mutation detection system for both KRT5 and KRT14, we identified four novel KRT5 mutations (IVS1-1G>C, K404E, A438D, E475K), two of which are outside the KRT5 hotspot domains, and three novel KRT14 mutations (IVS4+1G>A, L408M, L130P).

Phenotypic/genotypic correlations in patients with epidermolytic hyperkeratosis and the effects of retinoid therapy on keratin expression.

Dominant-negative mutations in the KRT1 and KRT10 genes cause epidermolytic hyperkeratosis, a rare form of ichthyosis sometimes associated with palmoplantar keratoderma. Although there is no permanent cure, some patients improve on retinoid therapy. More knowledge is needed, however, about the mechanism of action of retinoids and the genotypic/phenotypic correlations in this disease. Thirteen patients from 10 families with generalized disease and 2 sporadic patients with nevoid lesions were studied, probably representing most of the patients in Sweden and Norway. All patients, except one nevoid case, were known to have KRT1 or KRT10 mutations. Those with mutated keratin 1 (K1) invariably had associated keratoderma (n=6). In contrast, only 1 of 7 patients with K10 mutations had this problem (p = 0.0047). Five out of 6 patients with KRT10 mutations benefited from treatment with oral acitretin (5-25mg/day) or topical tretinoin/tazarotene, but none of the patients with KRT1 mutations derived any benefit. Quantitative analysis of K1 and K10 mRNA in skin biopsies obtained before and after retinoid therapy (n=8) showed no consistent down-regulation of mutated keratin that would explain the therapeutic outcome. Instead, the mRNA expression of K2e (a normal constituent of the upper epidermis) diminished especially in nonresponders. In contrast, K4 mRNA and protein (marker of retinoid bioactivity in normal epidermis) increased in almost all retinoid-treated patients. In conclusion, our study confirms a strong association between KRT1 mutations and palmoplantar keratoderma. Retinoid therapy is particularly effective in patients with KRT10 mutations possibly because they are less vulnerable to a down-regulation of K2e, potentially functioning as a substitute for the mutated protein in patients with KRT1 mutations.

Recurrent R156H mutation of KRT10 in a Japanese family with bullous congenital ichthyosiform erythroderma.

Recently, mutations of keratin 1 gene (KRT1) and keratin 10 gene (KRT10) have been reported in various patients with bullous congenital ichthyosiform erythroderma (BCIE). The substitution of arginine (R) to histidine (H) at amino acid residue 156 (R156H) of coiled 1A region is one of the most frequent mutations of KRT10. In this study, we searched for a mutation in KRT1 and KRT10 in a Japanese family with BCIE and detected mutation R156H in KRT10. Our search led to the detection of R156H. This mutation was not detected in 50 normal individuals. These results confirmed that codon 156 is a frequently mutated site, and that R156H in KRT10 is likely also to be a mutation hotspot in Japanese patients with BCIE.

A Premature Stop Codon Mutation in the 2B Helix Termination Peptide of Keratin 5 in a German Epidermolysis Bullosa Simplex Dowling–Meara Case

Epidermolysis bullosa simplex (EBS) is caused by defective assembly of keratin intermediate filaments in basal keratinocytes and recent studies indicated causal mutations in the keratin KRT5 and KRT14 genes. In this study, we describe a novel KRT5 mutation in a German sporadic case of EBS Dowling-Meara. Transition of G to T (nucleotide position 2334) leads to a premature stop codon (E477stop, residue 93 of the 2B helix) in the last residue of the highly conserved helix-termination peptide K/LLEGE of the 2B rod domain of keratin K5. This represents the first premature stop codon mutation identified within the K/LLEGE motif of any disorder reported so far that is caused by keratin mutations.