Keratin 1 gene mutation detected in epidermal nevus with epidermolytic hyperkeratosis

Since 1994, four cases of epidermal nevus with epidermolytic hyperkeratosis (EH) caused by keratin 10 gene mutations have been reported, although no keratin 1 (K1) gene mutation has yet been reported. We detected a K1 gene (KRT1) mutation in epidermal nevus with EH in a 10-year-old Japanese male. The patient showed well-demarcated verrucous, hyperkeratotic plaques mainly on the trunk, covering 15% of the entire body surface. No hyperkeratosis was seen on the palms or soles. He had no family history of skin disorders. His lesional skin showed typical granular degeneration and, ultrastructurally, clumped keratin filaments were observed in the upper epidermis. Direct sequence analysis of genomic DNA extracted from lesional skin revealed a heterozygous 5' donor splice site mutation c.591+2T>A in KRT1. This mutation was not detected in genomic DNA samples from the patient's peripheral blood leukocytes or those of other family members. The identical splice mutation was previously reported in a family with palmoplantar keratoderma and mild ichthyosis, and was demonstrated to result in a 22 amino-acid deletion p.Val175_Lys196del in the H1 and 1A domains of K1. To our knowledge, the present patient is the first reported case of epidermal nevus associated with EH caused by a K1 gene mutation in a mosaic pattern.     

表皮松解性角化过度型鱼鳞病两家系基因突变研究

目的 探讨两个表皮松解性角化过度型鱼鳞病（EHK）家系的基因突变情况。 方法 收集两个EHK家系的临床资料,提取外周血DNA,通过PCR扩增角蛋白基因KRT1和KRT10编码区的全部外显子及其侧翼序列并测序,以表型正常家系成员及50例健康人作为对照。结果 发现两个家系中患者均存在KRT10基因突变,分别为KRT10的剪接位点突变c.1030-2A > G和错义突变c.467G > A,在家系中健康人及健康对照者未发现上述突变。结论 剪接位点突变c.1030-2A > G和错义突变c.467G > A,可能分别是导致这两个家系临床表型的原因。     

A recurrent missense mutation of keratin 1 gene in a Chinese family with epidermolytic hyperkeratosis (severe palmoplantar hyperkeratosis, type 1)

Background Epidermolytic hyperkeratosis (EHK) is an autosomal dominantly inherited genodermatosis manifesting with blistering and erythroderma in infancy and widespread hyperkeratosis of the skin, particularly over flexural areas, in adulthood. It can be classified into six clinical phenotypes. Case report We report the case of a 25‐year‐old man who presented with severe palmoplantar thickening and hyperkeratosis over the flexures for nearly 24 years. Histopathological findings showed characteristic features of EHK, and EHK type PS‐1 (severe palmoplantar hyperkeratosis, type 1) was suspected. Further investigation revealed that his father, sister, and nephew (the son of his sister) were similarly affected. A heterozygous missense mutation in exon 7 of KRT1 (c.1436T>C), resulting in an isoleucine to threonine substitution at codon 479 (designated p.I479T), was detected in all affected individuals within the pedigree. Discussion Up to now, there has been one sporadic case and one family (including 14 affected individuals) with EHK type PS‐1 reported since DiGiovanna and Bale described 25 patients (from two families) with EHK type PS‐1 out of 51 patients (from 21 families) with EHK. Although the mutation (c.1436T>C) in KRT1 reported here is a recurrent one, it has not been reported in Chinese patients with EHK. It is interesting to note that the same mutation in KRT1 can cause different phenotypes of EHK. Conclusions We expand the clinical heterogeneity of EHK due to the same mutation (c.1436T>C) in KRT1 and enrich the database of the KRT1 gene mutations underlying EHK in the Chinese population.     

Identification of a de novo keratin 1 mutation in epidermolytic hyperkeratosis with palmoplantar involvement

Epidermolytic hyperkeratosis (EHK) (OMIM 113800) is a generalized skin disease with mostly autosomal dominant inheritance, caused by mutations in keratin 1 or keratin 10. These genes are expressed in suprabasal epidermal layers, resulting in abnormal keratin-intermediate filament cytoskeleton. We present a male patient with generalized hyperkeratosis involving palms and soles. In lesional skin massive hyperkeratosis and cytolysis in the suprabasal layers of the epidermis were observed. Immunohistochemistry staining for keratin 1 (and keratin 10) showed abnormal clumping in suprabasal keratinocytes. By electron microscopy perinuclear intermediate filament clumps were detected in the keratinocytes. A heterozygous missense mutation, designated L187F, was identified in exon 1 of the keratin 1 gene by direct sequencing. This mutation was not detected in his unaffected parents, indicative of a de novo mutational event. The homologous mutation (L187F, also designated L7F) in basal keratin genes keratin 5 or -14 causes epidermolysis bullosa simplex. The amount of keratin 1-mRNA in the patient's skin was not altered compared to controls.We propose that the severe EHK phenotype observed in our patient results from a dominant negative effect of the L187F mutant Keratin 1 allele exerted on keratin 10, the associated partner-keratin. These findings should be helpful for genetic counseling, prenatal diagnosis and studying molecular structure-function relationship in EHK.     

Two cases of primarily palmoplantar keratoderma associated with novel mutations in keratin 1

Mutations in keratin 1 were initially described in the classical form of bullous congenital ichthyosiform erythroderma (also known as epidermolytic hyperkeratosis). More recently the range of phenotypes associated with mutations in this gene has been extended to include annular ichthyosiform erythroderma and mild epidermolytic palmoplantar keratoderma. Here we present two novel mutations in the keratin 1 gene (KRT1): a 5' donor splice site mutation in exon 1 (591 + 2T > A) that predicts a 22 amino acid in-frame deletion in the keratin 1 1A domain; and an in-frame deletion in exon 7 (1376del24) that predicts a foreshortened 2B coiled-coil domain of keratin 1. In each case these mutations are associated with palmoplantar keratoderma and mild ichthyosis, largely limited to the flexural areas. These mutations appear to have a less damaging effect than previously reported mis-sense mutations sited in the helix boundary motifs. This report extends the range of phenotypes associated with mutations in KRT1.     

Splice site and deletion mutations in keratin (KRT1 and KRT10) genes: unusual phenotypic alterations in Scandinavian patients with epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis is a rare autosomal dominant inherited skin disorder caused by keratin 1 or keratin 10 mutations. Keratins are major structural proteins of the epidermis, and in keratinocytes committed to terminal differentiation the intermediate filaments are composed of keratin 1 and keratin 10 heterodimers. The majority of reported mutations (86.6%) are heterozygous single point mutations and most of these are located in the 1A and 2B regions of the highly conserved keratin alpha-helical rod domain. We have studied eight Scandinavian families with epidermolytic hyperkeratosis and identified three point mutations, two codon deletions, two splice site mutations, and a complex deletion/insertion. Two of the point mutations were in the KRT1 gene (F191C and K177N) and the other was in KRT10 (L453P). All three patients had associated palmoplantar keratoderma. The splice site mutations in KRT1 both caused a large deletion removing 22 codons (delta176-197) from the 1A helical domain. Codon deletions were found in KRT1 (delta170-173) and in KRT10 (delta161-162) in two patients with a severe phenotype. A final patient had a more complex mutation with a large deletion (442 bp) together with a large insertion (214 bp) of unknown origin that caused deletion of exon 6 in KRT1. In conclusion, we have found eight novel keratin mutations that cause epidermolytic hyperkeratosis with differing phenotypes. Even when a large part of keratin 1 (46 amino acids) is deleted, surprisingly mild phenotypes can result, suggesting that genotype-phenotype relationships in epidermolytic hyperkeratosis are complex and do not solely depend on the type of mutation but also depend on interactions between the behavior of the mutant protein and the cellular environment.     

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.     

Two cases of KRT1 mutation-associated epidermolytic ichthyosis without typical epidermolytic hyperkeratosis in the neonatal skin lesions

Epidermolytic ichthyosis (EI) is a rare genetic disorder of keratinization caused by mutations in either KRT1 or KRT10. Histopathologically, epidermolytic hyperkeratosis (EHK) is a hallmark of EI. Here, we report two EI cases in which KRT1 mutation was confirmed by molecular study, but without typical EHK present on skin biopsies performed within 1 week of age. Our cases demonstrate that EHK may not be evident in EI if skin biopsy is performed during the neonatal period.     

A novel heterozygous nonsense mutation of keratin 5 in a chinese family with Dowling–Degos disease

Background Dowling–Degos disease (DDD; MIM 179850) is an autosomal dominant genodermatosis caused by mutations in keratin 5 gene (KRT5). KRT5 is specifically expressed in basal layer of epidermis and plays an important role in protecting epithelial cells from mechanical and non‐mechanical stresses. Objective We analysed the molecular basis of DDD in a Chinese family. Methods Genomic DNA of the Chinese DDD family and a matched control cohort was isolated according to standard techniques. All exons of the KRT5 gene and adjacent exon–intron border sequences were amplified using PCR and directly sequenced. Results We identified a novel keratin 5 (K5) nonsense mutation designated c.C10T (p.Gln4X) in exon 1 of the KRT5 gene. Conclusion Our data expand the spectrum of mutations in the KRT5 gene underlying DDD.     

A usual frameshift and delayed termination codon mutation in keratin 5 causes a novel type of epidermolysis bullosa simplex with migratory circinate erythema

We report here two unrelated families in Japan and Korea having patients with a unique type of epidermolysis bullosa simplex and a novel mutation in the keratin gene KRT5, i.e., a frameshift and delayed stop codon inconsistent with any subtype described before. The patients showed migratory circinate erythema and multiple vesicles on the circular belt-like areas affected by erythema. Electron microscopy of skin biopsies showed a reduction in the number of keratin intermediate filaments in the basal cells without tonofilament clumping. We identified a novel heterozygous deletion mutation (1649delG of KRT5) in both cases. This deletion is predicted to produce a mutant keratin 5 protein with a frameshift of its terminal 41 amino acids and 35 amino acids longer than the wild-type keratin 5 protein due to a delayed termination codon. As the same abnormal elongated mutant KRT5 gene was found in the independent families, the predicted abnormal elongated keratin protein is likely to lead to an atypical clinical phenotype that has never been reported, possibly by interfering with the functional interaction between keratin and its associated proteins.     

一对先天性大疱性鱼鳞病样红皮病双胞胎患者表型与角蛋白1基因突变研究

目的 检测先天性大疱性鱼鳞病样红皮病双胞胎患者角蛋白1、10（KRT1、KRT10）基因突变情况,探讨致病基因与表型间的关系。方法 收集1对先天性大疱性鱼鳞病样红皮病双胞胎患者及家族成员的临床资料。提取该双胞胎患者及其兄、父、母的外周血DNA,PCR扩增KRT1和KRT10基因编码区全部外显子及其侧翼序列并测序,以100例健康人作为对照。结果 先证者男,11岁,全身皮肤反复起水疱、肥厚伴脱屑11年;其双胞胎弟弟有类似皮损。2例患者KRT1基因1号内含子第1位碱基发生突变（c.591 + 1G > A）,而家系中3例正常成员和无亲缘关系的100例健康对照均未发现该突变。结论 KRT1基因1号内含子第1位碱基突变（c.591 + 1G > A）可能为引起该双胞胎患者临床表型的病因。     

一个表皮松解性掌跖角化病家系的KRT1基因突变分析

目的 探讨一个中国汉族人表皮松解性掌跖角化病(EPPK)家系的角蛋白基因KRT1、KRT9、KRT10突变情况.方法 收集1个EPPK家系的临床资料,提取外周血DNA,通过PCR扩增角蛋白KRT1、KRT9、KRT10基因编码区的全部外显子及其侧翼序列并测序,以表型正常家系成员及50例健康人为正常对照.结果 发现家系内6例患者均存在KRT1基因错义突变c.1436T>C,导致第479位的异亮氨酸被苏氨酸取代(I479T),在家系中6例正常人及50例对照者未发现上述突变.结论 错义突变KRTI的c.1436T>C可能为导致该家系临床表型的主要原因.本例为国内首次发现的KRT1突变引起的EPPK家系.

Abstract：

Objective To analyze the mutations in keratin 1 (KRT1), KRT9 and KRT10 genes in a Chinese family with epidermolytic palmoplantar keratoderma (EPPK). Methods Clinical data were collected from a family with EPPK. Genomic DNA was extracted from the peripheral blood of 12 family members, including 6 patients and 6 unaffected members, as well as from 50 unrelated normal human controls. PCR was performed to amplify all the exons and flanking sequences of KRT1, KRT9 and KRT10 genes followed by DNA sequencing.Results A missense mutation C.1436T > C was found in the highly conserved helix termination motif of KRT1 gene of all the patients, resulting in a substitution of isoleucine by threonine at position 479 of the KRT1 protein. No mutation was found in the unaffected members or unrelated controls. Conclusions The missense mutation C.1436T > C in K.RT1 gene is likely to be the main cause of the phenotype of EPPK in this family.This is the first report of a pedigree with KRT1 gene mutation-induced EPPK in China.     

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).     

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.     

Epidermolytic hyperkeratosis in a Hispanic family resulting from a mutation in the keratin 1 gene

Epidermolytic hyperkeratosis (EHK; bullous congenital ichthyosiform erythroderma) is a genodermatosis resulting from mutations in either the keratin 1 (K1) or keratin 10 (K10) genes. It is characterized by erythroderma and blistering at birth, and the development of ichthyotic hyperkeratosis and palmoplantar keratoderma. A wide variety of mutations within the highly conserved helix initiation and 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 novel missense mutation designated L214P in a large Hispanic pedigree with EHK. The mutation is located in the highly conserved 1A segment of the alpha-helical rod domain. The presence of this mutation underscores the importance of sequence alterations located in the central rod domain in the pathogenesis of EHK.     

A large mutational study in pachyonychia congenita

Pachyonychia congenita (PC) is a rare autosomal dominant skin disorder characterized predominantly by nail dystrophy and painful palmoplantar keratoderma. Additional clinical features include oral leukokeratosis, follicular keratosis, and cysts (steatocysts and pilosebaceous cysts). PC is due to heterozygous mutations in one of four keratin genes, namely, KRT6A, KRT6B, KRT16, or KRT17. Here, we report genetic analysis of 90 new families with PC in which we identified mutations in KRT6A, KRT6B, KRT16, or KRT17, thereby confirming their clinical diagnosis. A total of 21 previously unreported and 22 known mutations were found. Approximately half of the kindreds had mutations in KRT6A (52%), 28% had mutations in KRT16, 17% in KRT17, and 3% of families had mutations in KRT6B. Most of the mutations were heterozygous missense or small in-frame insertion/deletion mutations occurring within one of the helix boundary motif regions of the keratin polypeptide. More unusual mutations included heterozygous splice site mutations, nonsense mutations, and a 1-bp insertion mutation, leading to a frameshift and premature termination codon. This study, together with previously reported mutations, identifies mutation hotspot codons that may be useful in the development of personalized medicine for PC.     

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 heterozygous frameshift mutation in the V1 domain of keratin 5 in a family with Dowling-Degos disease

Dowling-Degos disease (DDD) is an autosomal-dominant genodermatosis characterized by reticulate pigmentation of the flexures. By direct DNA sequencing, we have identified a frameshift mutation in exon 1 of KRT5 in the proband from an extended Spanish DDD kindred. Cloning of PCR products confirmed that this was a 2-bp deletion mutation, designated c.442delAG, leading to a premature termination codon in the V1 domain of the K5 polypeptide, designated p.S148fsX30. These data confirm that haploinsufficiency for K5 causes DDD and points to a prominent role for the keratin intermediate filament cytoskeleton within basal keratinocytes in epidermal pigment biology.     

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。