Intrafamilial phenotypic heterogeneity of epidermolytic ichthyosis associated with a new missense mutation in keratin 10

Mutations in the keratin 10 gene (KRT10) have been shown to underlie several forms of epidermolytic ichthyosis (EI), including generalized, annular and naevoid variants. We investigated an autosomal dominant pedigree with ichthyosis in which there was intrafamilial clinical heterogeneity, with the affected individual family members presenting with features of either erythrokeratoderma progressiva, annular EI, localized or superficial EI, or more generalized EI. Sanger sequencing identified a new heterozygous missense mutation (c.457C>A; p.Leu153Met) in KRT10 in all affected individuals. No additional mutations were identified in the genes for keratin 1 (KRT1) keratin 2 (KRT2), connexin 31 (GJB3) or connexin 30.3 (GJB4) that might account for the clinical heterogeneity seen in this family. Our findings illustrate the intrafamilial variability in phenotype and diverse clinical presentations that can occur in EI resulting from a single mutation in KRT10.     

Lethal autosomal recessive epidermolytic ichthyosis due to a novel donor splice‐site mutation in KRT10

Epidermolytic ichthyosis (EI; MIM 113800), previously named bullous congenital ichthyosiform erythroderma or epidermolytic hyperkeratosis, is a rare and clinically variable defect of cornification characterized by generalized erythema, erosions, scaling and easily breaking blisters that become less frequent later in life while hyperkeratosis increases. 1 EI is caused by dominant mutations in either KRT1 or KRT10, encoding keratin 1 (K1) and keratin 10 (K10), respectively. 1 Usually, mutations are missense substitutions into the highly conserved α‐helical rod domains of the proteins. 2 , 3 However, three inbred pedigrees in which EI is transmitted as a recessive trait due to KRT10 null mutations have been described. 4 - 6     

Novel and recurrent mutations in keratin 1 cause epidermolytic ichthyosis and palmoplantar keratoderma

Mutations in keratin genes underlie a variety of epidermal and nonepidermal cell‐fragility disorders, and are the genetic basis of many inherited palmoplantar keratodermas (PPKs). Epidermolytic PPK (EPPK) is an autosomal dominant disorder that can be due to mutations in the keratin 1 gene, KRT1. Epidermolytic ichthyosis (EI), the major keratinopathic ichthyosis, is characterized by congenital erythroderma, blistering and erosions of the skin. Causative mutations in KRT1 and KRT10 have been described, with PPK being present primarily in association with the former. We report four unrelated cases (one with sporadic EI and three with autosomal dominant PPK), due to two novel and two recurrent KRT1 mutations. Mutations in KRT1 are not only scattered throughout the keratin 1 protein, as opposed to being clustered, but can result in a range of phenotypes as further confirmed by these mutations, giving a complex genotype/phenotype pattern.     

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.     

Expanding the keratin mutation database: novel and recurrent mutations and genotype-phenotype correlations in 28 patients with epidermolytic ichthyosis

Background Epidermolytic ichthyosis (EI) is a hereditary keratinization disorder caused by mutations in the keratin 1 (KRT1) or keratin 10 (KRT10) genes. In most cases of severe EI, heterozygous single point mutations are found at the highly conserved helix boundary motifs of KRT1 and KRT10 that play a critical role in filament formation. The presence of palmoplantar keratoderma suggests KRT1 mutations, whereas KRT10 mutations in most instances give rise to the nonpalmoplantar variants. Objectives To identify the underlying mutations in patients with EI and to correlate genotype and phenotype. Methods Mutation analysis was performed in 28 patients with EI by direct sequencing of KRT1 and KRT10 genes. Results We identified 14 different mutations, of which four have not been published previously. Conclusions Identification of novel mutations and genotype–phenotype correlations in EI allows improved understanding of disease pathogenesis as well as better patient management.     

Recessive epidermolytic ichthyosis results from loss of keratin 10 expression,regardless of the mutation location

Epidermolytic ichthyosis (EI) is a rare skin disorder caused by mutations in the genes KRT1 and KRT10, and is usually inherited in an autosomal dominant fashion. Only five recessive mutations causing EI have been described, all of which are located in the central region of the KRT10 gene. In the current study, we aimed to identify the genetic defect underlying EI in a 12‐year‐old patient. Direct sequencing of the patient's genomic DNA revealed a novel homozygous nonsense mutation residing within the proximal part KRT10 first exon. The mutation was found to co‐segregate with the disease phenotype in an autosomal recessive fashion. Using real‐time quantitative PCR, we found an almost two‐fold decrease in KRT10 expression in the patient's skin compared with the skin of healthy controls. Western blot analysis showed complete absence of keratin 10 protein in the patient's skin, suggesting early protein degradation.     

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.     

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.     

Siemens大疱性鱼鳞病基因突变研究及文献回顾分析

目的确定1个Siemens大疱性鱼鳞病(ichthyosis bullosa of Siemens,IBS)家系的致病基因,探讨本病基因型、表型及两者间关系。方法收集1个IBS家系先证者及其父母的临床资料,采集他们和100例无亲缘关系的健康对照者的外周血标本,提取DNA。应用二代皮肤靶向测序包检测该家系的基因突变,Sanger测序验证。结果先证者及其母亲在KRT2基因存在杂合点突变c.1459G>A(p.E487K),而100例健康对照者及先证者父亲均未发现该突变。结论本研究在1个IBS家系中检测到1个致病突变位点KRT2基因c.1459G>A(p.E487K),同时丰富了IBS的基因型、表型及两者间的关系。     

Novel FLG mutations associated with ichthyosis vulgaris in the Chinese population

Loss-of-function mutations in the gene encoding filaggrin (FLG) can cause the semidominant keratinizing disorder ichthyosis vulgaris (OMIM 146700). To identify FLG mutations in three Chinese pedigrees with ichthyosis vulgaris, we sequenced the entire coding region of FLG in the proband of each pedigree. We found two novel FLG null mutations (c.477-478insA and c.6218-6219delAA) and a known mutation (c.3321delA). Both novel mutations were identified in the proband of pedigree 1; c.477-478insA was inherited from the proband's father, and the other was a de novo mutation. Neither of these two mutations was found in 200 unrelated controls. These findings extend the spectrum of functional FLG variants possibly causing ichthyosis vulgaris. Interestingly, the proband of pedigree 1 was compound heterozygous for these mutations, but had a mild phenotype, suggesting that an incomplete penetrance factor and perhaps other unknown factors may be involved in the pathogenesis of ichthyosis vulgaris.     

应用多重连接探针扩增技术检测X-性连锁鱼鳞病一家系STS基因

目的：检测X-性连锁鱼鳞病一家系STS基因突变情况。方法：提取先证者(男，31岁)及其父母外周血DNA，父母均无鱼鳞病临床表现，运用多重连接探针扩增技术检测所有成员的STS基因是否存在外显子缺失，若无外显子缺失，运用聚合酶链式反应特异性扩增STS基因，检测是否存在基因突变。结果：家系中先证者为STS基因半合子缺失，其母为STS基因杂合子缺失，其父亲未发现STS基因突变。家系中仅先证者出现鱼鳞病的临床表现。结论：STS基因缺失是该X-性连锁鱼鳞病患者发病的遗传因素。     

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.     

表皮松解性角化过度鱼鳞病一例

5岁女性患儿,全身皮肤潮红5年,出现干燥及角化增厚4年。皮损组织病理示:表皮显著角化过度,颗粒层细胞内见不规则的透明角质颗粒呈空泡样变性改变,棘层不规则增厚,真皮浅层血管周围少量炎性细胞浸润。基因突变检测示KRT10位点突变,基因编码区478号碱基由T变为A。诊断:表皮松解性角化过度鱼鳞病。给予局部外用0.1%维A酸乳膏每日2次及皮肤保湿剂治疗,40 d复诊时皮损明显好转,全身皮肤基本正常。     

表皮松解性掌跖角化病二家系基因突变检测

目的：检测表皮松解性掌跖角化病二家系患者致病基因。方法：收集二家系资料,提取二家系成员及100名（无亲缘关系）正常对照血样DNA,采取聚合酶链反应技术对KRT1、KRT9和KRT16基因进行扩增,并对其产物进行测序。结果：家系1先证者中检测到 KRT1基因突变c.598T>C（p.F200L）。家系2三例患者中检测到KRT9基因含杂合突变c.488G>A（p.R163Q）。而家系正常成员及家系外无亲缘关系的100名正常对照中均不存在以上突变。结论：本研究表皮松解性掌跖角化病二家系发病与KRT1、KRT9基因突变有关,且KRT1基因突变p.F200L为国内首次报道。     

X性联锁遗传鱼鳞病一家系的STS基因研究

目的 研究一 X性联锁遗传鱼鳞病(XLI)家系基因突变,探讨基因突变与临床表现的关系,为进一步开展基因诊断和基因治疗奠定基础。方法 应用PCR方法扩增家系中的先证者及其母亲及与该家系无关的50例正常人外周血基因组DNA STS基因的第一外显子和第十外显子。以角蛋白hHb6为引物,作内对照。结果 家系中先证者的STS基因全部缺失,而先证者之母和与该家系无关的50例正常人未发现缺失。先证者及先证者之母的内对照引物PCR扩增后都有产物。结论 该XLI家系存在STS基因缺失,该缺失引发出XLI特有的皮肤病变。     

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.     

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.     

常染色体隐性遗传性鱼鳞病一家系表型、基因型与皮损超微结构研究

目的 探讨常染色体隐性遗传性鱼鳞病家系临床表型、基因型及超微结构。方法 观察常染色体隐性遗传性鱼鳞病患者临床表现。用PCR扩增TGM1基因15个外显子及其邻近剪切位点,双向直接测序;取先证者背部皮损做透射电镜观察,记录电镜表现特征。结果 先证者临床表现介于板层状鱼鳞病及非大疱性鱼鳞病样红皮病之间,其弟弟为火棉胶婴儿。先证者、其弟及父亲3号外显子第551位碱基胞嘧啶（C）→胸腺嘧啶（T）,其编码的第143位氨基酸由精氨酸变为半胱氨酸（R143C）;先证者、其弟及母亲4号外显子第759位胞嘧啶（C）→胸腺嘧啶（T）,使第212位氨基酸由丝氨酸转变为苯丙氨酸（S212F）。电镜观察发现,先证者皮损不仅有Ⅱ型结构表现,也同时存在Ⅲ型结构特征。结论 该家系患者携带复合杂合突变,R143C属于热点区,S212F为新发现的位点。携带TGM1基因突变的先证者皮损电镜表现为Ⅱ型,但同时发现有Ⅲ型结构存在。     

A newborn presenting with congenital blistering

A baby girl was born to unrelated parents after an uneventful pregnancy. A dermatologic consultation was requested because of widespread skin blistering observed immediately after birth over most parts of the body. On examination, the baby appeared well. General physical inspection was unremarkable. Examination of the skin revealed the presence of numerous blisters and erosions scattered over the trunk, limbs, palms, and soles ( Fig. 1a,b ). The hair, nails, and buccal mucosa appeared normal. Routine laboratory tests were within normal limits. Although the parents did not recall any history of blistering disease in their respective families, the patient's mother, aged 29 years, mentioned the fact that she had suffered since early childhood from thickening of the palms and soles. A brother and her father displayed similar features. At the age of 20 years, she was treated with retinoids with worsening of her skin condition. Examination of the mother revealed diffuse palmoplantar keratoderma ( Fig. 1c ), as well as fine scaling visible over all parts of the body, except for the face. No blisters or erosions were observed. The parents did not consent to a skin biopsy from their daughter. A biopsy obtained from the mother's skin revealed orthohyperkeratosis, hypergranulosis, and marked vacuolar degeneration confined to the upper spinous and granular layers ( Fig. 1d ). The vacuolated keratinocytes contained irregularly shaped and enlarged keratohyaline granules. Electron microscopic examination of deparaffinized sections revealed perinuclear vacuolar changes and tonofilament clumping in the suprabasal layers of the epidermis ( Fig. 1e ). Taken together, these clinical and histologic findings suggested a diagnosis of epidermolytic hyperkeratosis (EHK; MIM113800), an autosomal dominant genodermatosis caused by mutations in keratin 1 (KRT1) or keratin 10 (KRT10) genes (Rothnagel JA, Dominey AM, Dempsey LD, et al. Mutations in the rod domains of keratins 1 and 10 in epidermolytic hyperkeratosis. Science 1992; 257: 1128–1130; Cheng J, Syder AJ, Yu QC, et al. The genetic basis of epidermolytic hyperkeratosis: a disorder of differentiation‐specific epidermal keratin genes. Cell 1992; 70: 811–819; Chipev CC, Korge BP, Markova N, et al. A leucine–proline mutation in the H1 subdomain of keratin 1 causes epidermolytic hyperkeratosis. Cell 1992; 70: 821–828).

Figure 1 Open in figure viewer PowerPoint Clinical and molecular analysis of epidermolytic hyperkeratosis (EHK). (a) Blistering is especially prominent over the palms and soles of the patient. (b) Extensive blistering and erosions are observed on the buttocks of the patient. (c) The newborn's mother displays marked palmar hyperkeratosis. (d) A biopsy obtained from the mother's skin demonstrates papillomatosis, orthohyperkeratosis, hypergranulosis, and marked vacuolar changes in the keratinocytes of the upper spinous and granular layers (hematoxylin and eosin, ×100). (e) Electron microscopic examination of a skin biopsy reveals both vacuolization and tonofilament clumping within the keratinocytes of the spinous layer (×3000). (f) Mutation analysis of a DNA sample obtained from the patient uncovers a heterozygous single nucleotide TC transition (arrow) at cDNA position 482 of the keratin 1 (KRT1) gene, which is predicted to result in the substitution of a proline residue for a leucine residue at position 161 of the amino acid sequence (right panel). The wild‐type sequence is shown in the left panel