Identification of a novel mutation in keratin 1 in a family with epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis (EHK) is a hereditary skin disorder typified by blistering due to cytolysis. One in 100,000 individuals is affected by this autosomal-dominant disease. The onset of the disease phenotype is typically at birth. Histological and ultrastructural examination of the epidermis shows a thickened stratum corneum and tonofilament clumping around the nucleus of suprabasal keratinocytes. Linkage studies localized the disease genes on chromosomes 12q and 17q which contain the type II and type I keratin gene clusters. Recently, several point mutations in the genes encoding the suprabasal keratins, K1 and K10, have been reported in EHK patients. We have investigated a large kindred affected by EHK and identified a new point mutation in the 2B region of keratin 1 (I107T), resulting from a T to C transition in codon 478.     

R156C mutation of keratin 10 causes mild form of epidermolytic hyperkeratosis

A 37-year-old Japanese male presented to us with persistent asteatotic skin with mild erythema on the trunk and extremities. Skin biopsy from the left knee showed marked epidermal acanthosis and hyperkeratosis, and milder granular degeneration. Ultrastructural analysis revealed clumping of the keratin filaments within suprabasal keratinocytes of the epidermis. Following direct sequencing, we found a single nucleotide substitution in one allele at the residue position 466 of the 1A rod domain segment (CGC to TGC, arginine to cysteine; R156C) in keratin 10. Clinical manifestations and molecular analysis indicated that R156C mutation in keratin 10 gene (KRT10) causes a mild form of epidermolytic hyperkeratosis (EHK) in the presented case.     

Epidermolytic hyperkeratosis with polycyclic psoriasiform plaques resulting from a mutation in the keratin 1 gene

Epidermolytic hyperkeratosis (EHK) is a genodermatosis caused by mutations in either the keratin 1 (K1) or keratin 10 (K10) genes, and characterized by erythroderma and blistering at birth, with development of a ribbed, ichthyotic hyperkeratosis and palmoplantar keratoderma. A wide variety of mutations within the highly conserved helix termination motifs of the central rod domains of the K1 or K10 genes correlate with the highly variable phenotypic severity observed in EHK. We report a unique EHK-like phenotype exhibiting autosomal dominant inheritance with variable expressivity in four affected individuals in a single family. Clinically, affected individuals manifest transient blistering at birth followed by chronic diffuse palmoplantar keratoderma without transgradiens. Intermittent flares of non-migratory polycylic erythematous psoriasiform plaques which worsen and abate in severity were present in all affected individuals, but showed immense individual variation in both severity and duration, ranging from weeks to months. Histopathologic examination of the psoriasiform plaques demonstrated the characteristic features of EHK. Sequencing of the K1 gene in affected family members revealed a heterozygous A-to-T transversion at nucleotide 1435 within exon 7, converting isoleucine (ATT) to phenylalanine (TTT), (I479F). The mutation resides within the highly conserved helix termination motif of the helix 2B segment of the K1 gene. This unique clinical phenotype and the associated K1 mutation have not been previously described, and it is referred to here as EHK with polycyclic, psoriasiform plaques (EHK/PPP).     

An asparagine to threonine substitution in the 1A domain of keratin 1: a novel mutation that causes epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis (EHK) is a congenital, autosomal dominant disorder of cornification characterized by hyperkeratosis and blister formation. The clinical manifestations are heterogeneous, with respect to the extent of body surface involvement, palmar and plantar hyperkeratosis and the presence of erythroderma. Point mutations in the genes encoding the suprabasal-specific keratins, keratins 1 and 10 have been identified in EHK patients. The inappropriate amino acid substitutions cause a collapse of the keratin filament network, resulting in cytolysis of the involved keratinocytes. We report a severe case of EHK with a single base pair mutation that causes a threonine for asparagine substitution in residue 8 (N8T) of the 1A region of the keratin 1 protein. This is the region involved in molecular overlaps between neighboring keratin heterodimers. These findings suggest that even conservative amino acid substitutions in overlap regions can cause tonofilament clumping.     

A novel mutation of keratin 9 in a large Chinese family with epidermolytic palmoplantar keratoderma

BACKGROUND: Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant inherited skin disorder characterized by diffuse yellow thickening of the skin of the palms and soles, sharply bordered with erythematous margins. Histologically and ultrastructurally, EPPK presents cytolysis of keratinocytes and abnormal aggregation of tonofilaments in the suprabasal layers of the epidermis. To date, 15 different mutations of the keratin 9 gene (KRT9) have been demonstrated to cause most cases of EPPK. OBJECTIVES: To identify the KRT9 mutation in a large Chinese family with EPPK. METHODS: Denaturing high-performance liquid chromatography (DHPLC), DNA sequencing and allele-specific polymerase chain reaction (AS-PCR) were used to screen exon 1 of the KRT9 gene for sequence variations. RESULTS: The DHPLC elution profiles of the DNA fragments amplified from the affected samples differed from those obtained from unaffected individuals, indicating that a sequence variation existed within the analysed fragment of KRT9. DNA sequencing revealed a novel insertion-deletion mutation in the exon 1 of KRT9, 497delAinsGGCT, resulting in the change of tyrosine(166) to tryptophan and leucine (Y166delinsWL). AS-PCR confirmed the mutation was not a common polymorphism. CONCLUSIONS: The results suggest the molecular basis of EPPK in this Chinese family and provide further evidence that mutations in the helix initiation motif of keratin 9 underlie Chinese EPPK.     

A novel mutation in the L12 domain of keratin 1 is associated with mild epidermolytic ichthyosis

Summary Background Epidermolytic ichthyosis (EI), previously termed bullous congenital ichthyosiform erythroderma or epidermolytic hyperkeratosis, is a clinically heterogeneous genodermatosis caused by mutations in the genes encoding the suprabasal keratins 1 and 10. Classical EI is clinically characterized by severe neonatal erythroderma, blistering and fragile skin in infancy, quickly subsiding with subsequent development of generalized scaling hyperkeratosis. We report three Dutch families with palmoplantar keratoderma and mild blistering, but without neonatal erythroderma and generalized scaling. A novel heterozygous missense mutation in the linker L12 domain of KRT1:c.1019A>G, p.Asp340Gly was found associated with this phenotype in these families. Objectives To investigate the effects of the novel KRT1:p.Asp340Gly and the one other previously reported KRT1:p.Asp340Val mutations on keratinocyte cytoskeleton formation and stress resistance. Methods Wild‐type and mutant pEGFP‐KRT1 fusion constructs were transfected into HaCaT cells and exposed to hypo‐osmotic shock. Haplotyping and genealogical studies were performed to investigate the possibility of a common founder for p.Asp340Gly. Results Cells transfected with either one of the keratin 1 L12 domain mutations showed significantly increased tonofilament aggregation. The haplotype around the KRT1 gene was shared in all affected family members of two families and a common founder was traced. Conclusions Our study supports the pathogenicity of the keratin 1 L12 domain mutations in vitro. These mutations are associated with a milder EI phenotype with pronounced palmoplantar keratoderma, and without neonatal erythroderma and scaling. The KRT1:p.Asp340Gly mutation in the Dutch families is likely to have arisen from a common founder.     

A keratin 14 'knockout' mutation in recessive epidermolysis bullosa simplex resulting in less severe disease

Epidermolysis bullosa simplex (EBS) is a blistering skin disease caused in most cases by mis-sense mutations in genes encoding the basal epidermal keratin (K) 5 and K14. The inheritance is usually autosomal dominant and the mutant keratin proteins appear to exert a dominant negative effect on the keratin intermediate filament cytoskeleton in basal keratinocytes. We report a child with a homozygous K14 mutation resulting in the complete absence of K14 protein in the epidermis; remarkably, he only had mild to moderate disease. Electron microscopy of a skin biopsy showed a marked reduction in numbers of keratin intermediate filaments in the basal keratinocytes. Immunofluorescence microscopy using monoclonal antibody LL001 against K14 showed no staining, suggesting a functional knockout of K14. Sequence analysis of genomic DNA revealed a homozygous mutation in codon 31 of K14 that resulted in a premature stop codon further downstream in exon 1. The child's mother, who is unaffected by the disease, is heterozygous for the mutation. The consanguineous father was unaffected and unavailable for testing. The resulting mRNA is predicted to encode a protein of 116 amino acids, of which the first 30 are identical to the normal K14 sequence, and the remaining 86 residues are mis-sense sequence. Four previously reported cases of autosomal recessive EBS with functional knockout of K14 were severely affected by blistering, in contrast to our patient in whom the predicted protein has only the first 30 amino acids of K14 and is therefore the closest to a true knockout of K14 protein yet identified.     

Identification of novel and known KRT5 and KRT14 mutations in 53 patients with epidermolysis bullosa simplex: correlation between genotype and phenotype

Background Basal epidermolysis bullosa simplex (EBS) is a hereditary skin blistering disorder resulting in most cases from missense mutations in the keratin 5 (KRT5) or keratin 14 (KRT14) genes. Objectives To identify the underlying mutations in different EBS subtypes and correlate genotype and phenotype. Methods Mutation analysis was performed in 53 patients with EBS and their families by direct sequencing of the KRT5 and KRT14 genes. Results We identified 39 different mutations, of which 15 have not been published previously. Three novel deletion/insertion mutations, among them one in‐frame duplication, were associated with the rare phenotype of EBS with mottled pigmentation. We identified for the first time a patient with compound heterozygosity for KRT5 mutations causing Dowling–Degos disease and EBS. Conclusions Identification of novel mutations and genotype–phenotype correlations in EBS allow improved understanding of disease pathogenesis as well as better patient management.     

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.     

伴移行性环形红斑的单纯性大疱性表皮松解症一家系报道及基因检测

目的:单纯性大疱性表皮松解症伴有移行性环状红斑(EBS-Migr)是EBS的一种罕见亚型,是一种常染色体显性遗传病,本文报道一家系,并进行基因检测。方法:收集临床资料,提取患儿及其父母外周血DNA,对患儿及其父母进行全基因组外显子测序,经生物学分析,获得致病变异;再采用Sanger测序法进行验证。结果:患儿及其父亲KRT5外显子9存在杂合突变(移码缺失c.1653＿1654delCT),其母亲未发现该突变。结论:该患儿诊断为伴移行性环状红斑的单纯性大疱性表皮松解症,致病机制为KRT5外显子9发生杂合突变(移码缺失c.1653＿1654delCT),既往未见报道。     

Atypical epidermolysis bullosa simplex with a missense keratin 14 mutation p.Arg125Cys

Epidermolysis bullosa (EB) is a group of hereditary autosomal dominant bullous diseases. EB is divided into four major phenotypes: intraepidermal EB (or EB simplex), junctional EB, dermolytic EB and mixed EB (Kindler syndrome). EB simplex is further divided into three subtypes: localized EB simplex, Dowling-Meara EB simplex and other generalized EB simplex. We report a 28-year-old man with EB simplex with a missense keratin 14 mutation p.Arg125Cys associated with clumping of keratin filaments and acantholysis in mainly the spinous cells and basal cells. Immunohistochemistry revealed that the broader expression of keratin 5 and 14 was observed in the epidermis, while the expression of keratin 1/10 was quite normal. Dysregulated expression of keratin 5/14 may hinder some functions or roles of keratin 1/10, namely filament assembly of keratin 1/10 in spinous cell integrity, although the expression of keratin 1/10 was not affected and this has not been demonstrated before.     

A novel mutation of keratin 5 in epidermolysis bullosa simplex with migratory circinate erythema

Epidermolysis bullosa simplex migratory circinate erythema (EBS-Migr) is an uncommon subtype of EBS. We report a case of EBS-MIGR with a novel heterozygous pathogenic mutation in exon 9 (frameshift deletion c.1650delC) and likely benign heterozygous mutation in exon 2 (missense c.591C > A) of keratin 5. This novel pathogenic mutation in KRT5 expands the molecular spectrum of this rare subtype of EBS.     

Atypical epidermolytic palmoplantar keratoderma presentation associated with a mutation in the keratin 1 gene

BACKGROUND: Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant genodermatosis characterized by epidermolytic hyperkeratosis strictly confined to the palms and soles, and usually associated with mutations in the keratin K9 gene (KRT9). Mutations in the keratin K1 gene (KRT1) have been shown to underlie a variety of phenotypes typically involving generalized epidermolytic hyperkeratosis, but in some cases the phenotype can be more regionally restricted. OBJECTIVES: To identify the genetic defect in two unrelated families initially presenting with EPPK but where careful examination revealed hyperkeratosis extending on to the proximal wrist flexure. Methods Linkage analysis and DNA sequencing. RESULTS: We found that this phenotype is caused by a heterozygous missense mutation in the K1 gene, designated I479T. This mutation lies in the highly conserved helix termination motif of K1, previously shown to be important for keratin assembly and filament formation. In general, mutations in this region of keratins are associated with more severe disease phenotypes. However, K1 mutations in this region and the I479T mutation in particular have previously been associated with both severe and mild bullous congenital ichthyosiform erythroderma phenotypes. When further clinical enquiries were made, several affected individuals in the families studied here were found to have had transient flexural peeling and hyperkeratosis in the neonatal period. CONCLUSIONS: K1 mutations may underlie a phenotype closely resembling EPPK. A history of transient flexural peeling and hyperkeratosis in childhood and palmoplantar keratoderma which extends beyond the boundary of the palmoplantar margins may indicate a K1 mutation rather than a K9 defect. As K1 mutations are also associated with severe widespread phenotypes, with important implications for prognostic and genetic counselling, whole body examination is recommended for patients presenting with EPPK.     

Weber-Cockayne亚型单纯型大疱性表皮松解症一家系报告

目的:研究Weber-Cockayne亚型单纯型大疱性表皮松解症(EBS-WC)一家系的基因突变,并进行产前诊断。方法:应用PCR及DNA直接测序方法明确突变位点,针对所发现的突变以限制性内切酶片段长度多态性(RFLP)分析加以验证,在此基础上于妊娠24周时对从胎儿羊水所提取的DNA进行测序及酶切验证。结果:该家系患者存在角蛋白(keratin,KRT)5基因突变:第7外显子第1388位碱基由胸腺嘌呤突变为胞嘧啶,导致第463位氨基酸由亮氨酸变为脯氨酸(L463P)。50名健康对照者不存在此突变。羊水细胞DNA不存在此突变的胎儿,出生后未患大疱性表皮松解症。结论:KRT5第7外显子的突变是引起该家系临床症状的特异性突变。