A novel mutation in the second half of the keratin 17 1A domain in a large pedigree with delayed-onset pachyonychia congenita type 2

Pachyonychia congenita type 2 (PC-2), also known as Jackson-Lawler type PC, is an autosomal dominant disorder characterized by hypertrophic nail dystrophy associated with focal keratoderma and multiple pilosebaceous cysts. We report a large Chinese pedigree of typical delayed-onset PC-2 that includes 19 affected members. Direct sequencing of PCR products revealed a novel heterozygous 325A-->G mutation in the affected members. This mutation predicts the substitution of asparagine by aspartic acid in codon 109 (N109D) located in the second half of the keratin 17 1A domain, where similar mutation in keratin 5 is associated with the mild Weber-Cockayne form of epidermolysis bullosa simplex.     

先天性厚甲症2家系中角蛋白16和17的基因突变

目的了解先天性厚甲症Ⅰ型(PC-Ⅰ)及Ⅱ型(PC-Ⅱ)患者家系的基因突变。探讨其基因突变和临床表现的关系。方法扩增外周血基因组DNA中角蛋白16基因的第1~6外显子及K17基因的第1外显子,对PCR产物进行序列分析。结果PC-Ⅰ家系(家系1)中患者K16基因第127位密码子由CGC突变CCC,导致K16角蛋白1A区的精氨酸由脯氨酸替代(R127P);PC-Ⅱ家系(家系2)中2例患者K17基因第99位密码子由CTG突变为CCG,导致K17角蛋白1A区的亮氨酸由脯氨酸替代(L99P),而这两个家系中的正常人及与此两家系无关的50例正常人未发现此突变。结论该PC-Ⅰ家系存在角蛋白16的R127P突变,PC-Ⅱ家系存在角蛋白17的L99P突变。3例厚甲症患者检测到的2个角蛋白突变均由K16及K17发生错义突变,导致其编码的相应氨基酸由脯氨酸替代。此类突变可引发较重的临床表现,即呈现典型PC-Ⅰ型或PC-Ⅱ型,不会呈现其他较轻的临床亚型。     

Keratin 17 mutations cause either steatocystoma multiplex or pachyonychia congenita type 2

Pachyonychia congenita type 2 (PC-2; Jackson–Lawler syndrome) is an autosomal dominant disorder characterized by hypertrophic nail dystrophy, mild focal keratoderma, multiple pilosebaceous cysts and other features of ectodermal dysplasia. Keratin 17 (K17) is a differentiation-specific keratin expressed in the nail bed, hair follicle, sebaceous gland and other epidermal appendages. Previously, we have demonstrated that PC-2 is caused by mutations in K17 and that similar mutations in this gene can present as steatocystoma multiplex with little or no nail dystrophy. Here, we describe three unrelated kindreds carrying K17 mutations. Two of these families have identical missense mutations (R94C) in the 1A domain of K17. However, while affected members of one kindred have the classical features of PC-2, affected persons in the other family have the steatocystoma multiplex phenotype. In a third family with PC-2, mutation N92S was detected, bringing the total number of distinct mutations reported in K17 thus far to 11. These results demonstrate that K17 mutations commonly underlie both PC-2 and steatocystoma multiplex and that the alternate phenotypes which arise from these genetic lesions in K17 are independent of the specific mutation involved.     

Keratin 17 mutation in pachyonychia congenita type 2 patient with early onset steatocystoma multiplex and Hutchinson-like tooth deformity

Pachyonychia congenita type 2 (PC-2) is an autosomal dominant disorder characterized by hypertrophic nail dystrophy, focal keratoderma, multiple pilosebaceous cysts, and other features of ectodermal dysplasia. It has been demonstrated that PC-2 is caused by mutations in the keratin 17 and keratin 6b genes. In this report, we describe a missense mutation in the keratin 17 gene, M88T, in a Korean patient whose phenotype included early onset steatocystoma multiplex and Hutchinson-like tooth deformities along with other typical features of PC-2 such as hypertrophic nails, natal teeth and follicular hyperkeratosis.     

Mutation report: identification of a germline mutation in keratin 17 in a family with pachyonychia congenita type 2

Pachyonychia congenita type 2 (PC-2), also known as Jackson-Lawler type PC, is an autosomal dominant disorder characterized by hypertrophic nail dystrophy associated with focal keratoderma and multiple pilosebaceous cysts. It has been demonstrated that PC-2 is associated with germline mutations in the keratin 17 (K17) gene and in its expression partner keratin 6b. In this report, we describe a novel germline mutation in K17, M88T, in a family with PC-2.     

Clinical and pathological features of pachyonychia congenita

Pachyonychia congenita (PC) is a rare genodermatosis affecting the nails, skin, oral mucosae, larynx, hair, and teeth. Pathogenic mutations in keratins K6a or K16 are associated with the PC-1 phenotype whereas K6b and K17 mutations are associated with the PC-2 phenotype. Analysis of clinical, pathological, and genetic data from the literature and two research registries reveal that >97% of PC cases exhibit fingernail and toenail thickening, and painful plantar keratoderma. Prospective evaluation of 57 PC patients from 41 families revealed variable clinical findings: hyperhidrosis (79%), oral leukokeratosis (75%), follicular keratosis (65%), palmar keratoderma (60%), cutaneous cysts (35%), hoarseness or laryngeal involvement (16%), coarse or twisted hair (26%), early primary tooth loss (14%), and presence of natal or prenatal teeth (2%). Stratification of these data by keratin mutation confirmed the increased incidence of cyst formation and natal teeth among PC-2 patients, although cysts were more commonly seen in PC-1 than previously reported (25%-33%). Previously unreported clinical features of PC include development of painful oral and nipple lesions during breastfeeding, copious production of waxy material in ears, and inability to walk without an ambulatory aid (50%). Possible pathogenic mechanisms are discussed with respect to the clinicopathologic and genetic correlations observed.     

一先天性厚甲家系角蛋白基因突变鉴定

目的 探讨一个先天性厚甲家系角蛋白基因突变。方法 用PCR及Sanger测序技术对先天性厚甲家系先症者KRT17基因所有外显子和KRT6B基因编码螺旋起始和终止区域序列进行突变鉴定,针对发现的可疑位点,Sanger测序检测家系其他成员该位点的变异情况。结果 基因检测结果表明,家系患者KRT17基因错义突变c.263T 〉 C,该突变导致角蛋白17（K17）第88位氨基酸由蛋氨酸变成苏氨酸（p.M88T）,KRT6B基因未见异常。结论 KRT17基因c.263 T 〉 C（p.M88T）突变是该先天性厚甲家系致病基因突变。     

A spectrum of mutations in keratins K6a, K16 and K17 causing pachyonychia congenita

BACKGROUND: Pachyonychia congenita (PC) is a rare autosomal dominant keratin disorder, subdivided into two major variants, PC-1 and PC-2. Predominant characteristics include hypertrophic nail dystrophy, focal palmoplantar keratoderma and oral leukokeratosis. Multiple steatocystomas that develop during puberty are a useful feature distinguishing PC-2 from PC-1. At the molecular level it has been shown that mutations in keratin K6a or K16 cause PC-1 whereas those in K6b or K17 lead to PC-2. OBJECTIVE: To identify mutations in 22 families presenting with clinical symptoms of either PC-1/focal non-epidermolytic palmoplantar keratoderma (FNEPPK) or PC-2. METHODS: Mutation analysis was performed on genomic DNA from PC patients by direct sequencing. RESULTS: Here, we report four new missense and five known mutations in K6a; one new deletion and three previously identified missense mutations in K16; plus one known mutation in K17. CONCLUSION: With one exception, all these heterozygous mutations are within the highly conserved helix boundary motif regions at either end of the keratin rod domain. In one sporadic case, a unique mutation in K16 resulting in deletion of 24bp was found within the central rod domain, in a child with a phenotype predominantly consisting of focal plantar keratoderma. The identification of mutations in cases of PC is prerequisite for future development of gene-specific and/or mutation-specific therapies.     

多发性脂囊瘤角蛋白17基因的突变研究

目的:研究多发性脂囊瘤(SM)角蛋白17基因的突变,为进一步开展基因诊断和基因治疗奠定基础。方法:抽取多发性脂囊瘤患者、患者父母以及100例正常人静脉血提取基因组DNA,采用聚合酶链反应(PCR)的方法对角蛋白17外显子1及其侧翼和外显子6进行扩增,并对其PCR产物直接进行双向测序以检测突变。结果:在家系中两例患者第42位密码子由CTG突变为CCG,结果导致角蛋白17 V1区杂合错义突变(L42P),即亮氨酸由脯氨酸替代,而此家系中的正常人和与该家系无关的100例正常人的DNA测序结果未发现此突变。结论:此家系中患者表型可能由角蛋白17基因头区的L42P突变所致。     

The genetic basis of pachyonychia congenita

In 1994, the molecular basis of pachyonychia congenita (PC) was elucidated. Four keratin genes are associated with the major subtypes of PC: K6a or K16 defects cause PC-1; and mutations in K6b or K17 cause PC-2. Mutations in keratins, the epithelial-specific intermediate filament proteins, result in aberrant cytoskeletal networks which present clinically as a variety of epithelial fragility phenotypes. To date, mutations in 20 keratin genes are associated with human disorders. Here, we review the genetic basis of PC and report 30 new PC mutations. Of these, 25 mutations were found in PC-1 families and five mutations were identified in PC-2 kindreds. All mutations identified were heterozygous amino acid substitutions or small in-frame deletion mutations with the exception of an unusual mutation in a sporadic case of PC-1. The latter carried a 117 bp duplication resulting in a 39 amino acid insertion in the 2B domain of K6a. Also of note was mutation L388P in K17, which is the first genetic defect identified in the helix termination motif of this protein. Understanding the genetic basis of these disorders allows better counseling for patients and paves the way for therapy development.     

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.     

Pruritic bluish-black subcutaneous papules on the chest

Steatocystoma multiplex (SM) is characterized by multiple dermal cysts involving the pilosebaceous glands. Although most presenting cases are sporadic, there is a rare familial syndrome involving a mutation in keratin 17 (K17) that is inherited in an autosomal dominant fashion. SM often presents concomitantly with eruptive vellus hair cysts (EHVS) and pachyonychia congenital type 2 (PC-2). We report a sporadic case of SM in a 21-year-old man.     

表皮松解性掌跖角化病一家系KRT9基因突变检测

目的：检测一表皮松解性掌跖角化病(epidermolytic palmoplantar keratoderma,EPPK)家系中患者及其家族成员的KRT9基因突变。方法：收集该EPPK家系先证者及其家族成员临床资料,提取他们及100例无亲缘关系的健康对照外周血DNA,PCR扩增KRT9基因编码区的全部外显子及其侧翼序列,对产物直接测序,同时进行突变点的功能预测。结果：该家系所有患者的KRT9基因1号外显子第482位碱基均发生错义突变c.482A>G(p.Asn161Ser)。家系中未患病者及100名正常对照中均未发现此突变。SIFT和Polyphen-2软件预测c.482A>G(p.Asn161Ser)突变为有害变异位点。结论：KRT9基因的突变c.482A>G(p.Asn161Ser)可能是导致该家系发生表皮松解性掌跖角化病的原因。     

Pachyonychia congenita tarda affecting only the nails

A 42-year-old woman presented with complaints of rapidly progressing thickening and yellowish discoloration of the nails for the past 24 months. All nails were affected and fingernails were more thickened than toenails. Her palms and soles were normal. Keratosis pilaris, palmoplantar blistering, hyperhidrosis, leukokeratosis, alopecia, dental malformation, corneal abnormalities and epidermoid cysts were absent. This patient has pachyonychia congenita tarda with clinical manifestations limited to nail involvement.     

单纯型大疱性表皮松解症Dowling-Meara亚型基因突变检测

目的探讨单纯型大疱性表皮松解症Dowling-Meara亚型(EBS-DM)的遗传学发病机制。方法报告1例单纯型大疱性表皮松解症Dowling-Meara亚型(EBS-DM)的家系,选择该家系中2例患者、1名正常人及50名无血缘关系者,扩增外周血基因组DNA中编码角蛋白14(K14)和角蛋白5(K5)的所有外显子,PCR产物进行序列分析。结果在此EBS-DM家系患者中,位于K14第1外显子的125位密码子由CGC突变CAC,导致精氨酸由组氨酸替代(R125H),而家系中正常人及与家系无关的50例正常人无此突变。结论该EBS-DM家系患者的K14第1外显子存在R125H突变。     

Eruptive vellus hair cyst and epidermoid cyst in a patient with pachyonychia congenita

We report the first case of pachyonychia congenita (PC) associated with both eruptive vellus hair cyst (EVHC) and epidermoid cyst. The patient is a 12-year-old Japanese girl who presented with two natal teeth at birth. She had thickening and discoloration of the fingernails and toenails, plantar hyperkeratosis, palmar-plantar hyperhidrosis and multiple cutaneous cysts. Histologic examination revealed EVHC and epidermoid cyst.     

先天性厚甲症研究进展

先天性厚甲症是一种少见的常染色体显件遗传性皮肤病,临床上分为两型,影响指(趾)甲、皮肤、口腔黏膜、喉、头发和牙齿,以指(趾)甲过度增厚伴营养小良为主要特征.日前在分子水平已经阐明Ⅰ型先天性厚甲症是由角蛋白基因K6a和K16突变引起,而Ⅱ型先天性厚甲症则是由角蛋白基因K6b和K17突,变引起.在治疗方而,主要是对症治疗,基因治疗已成为研究的热点,特别在应用小干扰RNA(siRNA)治疗先天性厚甲症的研究方面取得进展,已成为治疗遗传性皮肤病的一个新的方向.     

先天性厚甲症研究进展

先天性厚甲症是一种少见的常染色体显性遗传性皮肤病,临床上分为两型,影响指（趾）甲、皮肤、口腔黏膜、喉、头发和牙齿,以指（趾）甲过度增厚伴营养不良为主要特征。目前在分子水平已经阐明I型先天性厚甲症是由角蛋白基因K6a和K16突变引起,而Ⅱ型先天性厚甲症则是由角蛋白基因K6b和K17突变引起。在治疗方面,主要是对症治疗,基因治疗已成为研究的热点,特别在应用小干扰RNA（siRNA）治疗先天性厚甲症的研究方面取得进展,已成为治疗遗传性皮肤病的一个新的方向。     

斑驳病一家系调查及基因突变研究

目的 探讨中国汉族斑驳病一家系的临床特征和基因突变情况。方法 对该家系临床资料进行收集、整理、照相存档及临床遗传学特征分析,并绘制系谱图。提取家系成员和正常人对照者外周血基因组DNA,采用PCR及DNA直接测序的方法对该家系进行基因突变检测。结果 该家系成员共73人。根据典型的临床特征,先证者及其他患者共14例均确诊为斑驳病,遗传方式为常染色体显性遗传。家系中患者均存在KIT基因13号外显子第1900位ATGA插入（1900insATGA）,导致第634位密码子处出现移码突变,KIT蛋白多肽翻译提前终止于第641位密码子。家系其他成员及50例正常人对照者未发现此突变。该突变位点此前未见报道。结论 一种新的KIT基因突变（1900insATGA）可能是引起该斑驳病家系临床表型的原因。     

X-性连锁鱼鳞病一家系类固醇硫酸酯酶基因研究

目的 检测一个中国汉族人X-性连锁鱼鳞病家系的类固醇硫酸酯酶(STS)基因突变情况.方法 收集1个X-性连锁鱼鳞病家系的临床资料,提取外周血DNA,通过PCR扩增外周血基因组DNA类固醇硫酸酯酶基因的第1和第10外显子,以表型正常家系成员及50例健康人为正常对照.结果 家系内全部患者均存在STS基因的完全缺失,即10个外显子均缺失,家系中正常人及对照者未发现上述缺失.结论 STS基因的完全缺失可能为导致该家系临床表型的主要原因.

Abstract：

Objective To detect the steroid sulfatase (STS) gene mutation in a Chinese pedigree with X-linked ichthyosis (XLI). Methods Genomic DNA was extracted from the peripheral blood of 3 affected patients and unaffected members in this family and 50 unrelated healthy volunteers followed by the amplification of the exon 1 and exon 10 of STS gene by PCR. Results Complete deletion of the exon 1 to 10 of STS gene was detected in all the patients in this pedigree with XLI, while no mutation was found in this gene in unaffected members of this family or normal human controls. Conclusion The complete deletion of STS gene is likely to be the main cause of the phenotype of XLI in this family.