Novel splice site mutation in keratin 1 underlies mild epidermolytic palmoplantar keratoderma in three kindreds

We report a novel mutation in the exon 6 splice donor site of keratin 1 (G4134A) that segregates with a palmoplantar keratoderma in three kindreds. The nucleotide substitution leads to the utilization of a novel in-frame splice site 54 bases downstream of the mutation with the subsequent insertion of 18 amino acids into the 2B rod domain. This mutation appears to have a milder effect than previously described mutations in the helix initiation and termination sequence on the function of the rod domain, with regard to filament assembly and stability. Affected individuals displayed only mild focal epidermolysis in the spinous layer of palmoplantar epidermis, in comparison with cases of bullous congenital ichthyosiform erythroderma also due to keratin 1 mutations, which show widespread and severe epidermolysis. This study describes a novel mutation in KRT1 that results in a phenotype distinct from classical bullous congenital ichthyosiform erythroderma.     

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.     

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.     

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.     

Functional analysis of splice site mutations in the human hairless (HR) gene using a minigene assay

Background Congenital atrichia is a rare autosomal recessive form of isolated alopecia which is caused by mutations in the human hairless (HR) gene. Patients are born with normal hair that is shed almost completely and irreversibly during the first weeks of life. Objectives To investigate the molecular genetic basis of congenital atrichia in two patients, and to analyse the functional consequences of one newly identified and all seven previously identified HR splice site mutations using a minigene assay. Methods Molecular analysis of the HR gene was performed by direct DNA sequencing. To analyse the functional consequences of the splice site mutations, the respective sequences were cloned into a vector which allows directed splicing. After transfection of COS7 cells, isolation of RNA and cDNA synthesis, sequencing was performed to analyse the products. Results Two novel mutations were identified: an insertion in exon 2 (c.485insT; p.C162LfsX17), and a splice site mutation (c.2847–1G>A). In vitro analysis revealed aberrant splicing for all eight of the investigated HR splice site mutations. Comparison with the results of two biocomputational programs (neural network splice server and CRYP‐SKIP) and calculation of consensus values revealed that the predictions of these two programs were consistent in only five and two of the eight mutations, respectively. Conclusions This is the first report to analyse the consequences of HR splice site mutations using a cell‐based in vitro assay. The results highlight the importance of performing splicing experiments to clarify the consequences of putative splice site mutations.     

Novel KRT14 mutation causing epidermolysis bullosa simplex with variable phenotype

About 75% of cases of epidermolysis bullosa simplex result from mutations in KRT5 and KRT14 genes. Here, we report a family with a novel heterozygous missense mutation p.Leu418Gln in the KRT14 gene causing EBS of phenotype varying from EBS‐loc to EBS‐gen intermed. To the best of our knowledge, the family reported by us is the largest one in which two different phenotypes can be distinguished. The molecular dynamics simulations show that p.Leu418Gln mutation results in clear disruption of intermolecular π‐stacking between KRT14:Tyr415 and KRT5:Tyr470, which in turn may affect putative phosphorylation site at KRT14:Thr414. This study further supports the importance of the EIATYR/KLLEGE motif in maintaining structural stability of KRT14:KRT5 heterodimer and indicates that physical properties of introduced amino acid can modulate the disease severity. The results obtained indicate further need of genotype–phenotype studies in EBS. In conclusion, genotype‐based prognosis should be given to patients with caution.     

A novel mutation of keratin 9 gene (R162P) in a Japanese family with epidermolytic palmoplantar keratoderma

Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant inherited skin disorder characterized by hyperkeratosis of the skin over the palms and soles. Mutations in keratin 9 gene (KRT9) have been demonstrated in EPPK. In this study, we screened a Japanese family with EPPK for KRT9 mutation by polymerase chain reaction amplification of genomic sequences, followed by heteroduplex analysis and direct nucleotide sequencing. The mutation consisted of a G-to-C transversion at codon 162 in exon 1, which was located in the hot spot of the mutations that have been reported previously (R162Q and R162W). However, the amino acid substitution was proline for arginine (R162P) in the 1A rod domain, the highly conserved helix initiation motif of keratin 9. Our result illustrates the repertoire of KRT9 mutation underlying the occurrence of EPPK in a Japanese family and is an important contribution to the investigation of the genotype/phenotype correlation.     

Identification of a missense mutation causing exon skipping in a neurofibromatosis type 1 patient

Neurofibromatosis type 1 (NF1), caused by germ line mutations of the NF1 tumor‐suppressor gene, is one of the most common autosomal dominant disorders. Here, we reported a NF1 patient with the mutation NF1 c.4367+1G>C. This sequence change locates at the first nucleotide of NF1 intron 32 within the consensus splice site. Compared with NF1 c.4367G>C predicted to potentially damage the wild‐type donor site at c.4367, the NF1 c.4367+1G>C potentially abolishes this wild‐type donor site by in silico analysis. In vitro minigene assay revealed that the NF1 c.4367+1G>C may cause exon 32 skipping. Our result provides further evidence for its clinical significance of NF1 c.4367+1G>C in clinical practise.     

A novel frameshift truncation mutation in the V2 tail domain of KRT1 causes mild ichthyosis hystrix of Curth–Macklin

Ichthyosis hystrix, Curth–Macklin type (IHCM) is an extremely rare autosomal dominant dermatosis caused by mutations in the keratin genes, KRT1 or KRT10, which often manifests as extensive, dark, spiky or verrucous plaques and severe palmoplantar keratoderma. We report a novel frameshift truncation mutation, c.1596_1597insAT (p.Gly533Metfs*82) in exon 7 (V2 tail domain) of KRT1, which, by replacing the glycine–serine-rich tail of KRT1 with a series of 75 alanine-rich amino acids, produces a mild IHCM phenotype. The patient with the mutation presented with localized ichthyosis and progressive hyperkeratosis of the palms and soles with no history of blistering.     

Whole‐exome sequencing diagnosis of two autosomal recessive disorders in one family

Autosomal recessive congenital ichthyosis (ARCI) is a genetically heterogeneous disorder for which subtyping through molecular analysis can help determine the eventual phenotype and prognosis. We used whole‐exome sequencing to identify a new homozygous splice‐site mutation in ST14 (IVS5+1G>A), encoding matriptase, in a 4‐year‐old girl with ARCI from a consanguineous Kuwaiti family. Clinically, she also had hypotrichosis, which supported a diagnosis of ARCI type 11. Only four previous examples of pathogenic mutations in ST14 have been reported, and our findings expand the genotype–phenotype correlation for this subtype of ARCI. Our patient was the second child born to these parents; the first (deceased) and third children had congenital brain and eye abnormalities, of uncertain aetiology and with no precise diagnosis. Further analysis of our patient's exome dataset revealed heterozygosity for a splice‐site mutation in POMT1 (IVS4+1G>T), encoding the protein O‐mannosyltransferase, a gene implicated in Walker–Warburg syndrome. DNA sequencing in the third child showed homozygosity for this mutation in POMT1. The first‐cousin parents were both heterozygous for the splice‐site mutations in ST14 and POMT1. In this family, whole‐exome sequencing provided accurate subtyping of a form of ARCI in one child and provide an explanation for an undiagnosed developmental disorder in two other children, findings that improve the prospects for diagnostic accuracy and genetic counselling, and demonstrate the impact of next‐generation sequencing technologies on clinical genetics.     

Heterogeneous mutations of the ATP2C1 gene causing Hailey–Hailey disease in Hong Kong Chinese

Background Hailey–Hailey disease (HHD) is a rare autosomal dominant dermatosis. It causes suprabasilar acantholysis leading to vesicular and crusted erosions affecting the flexures. Mutation of ATP2C1 gene encoding the human secretory pathway Ca²⁺/Mn²⁺‐ATPase (hSPCA1) was identified to be the cause of this entity. Objective The aim of this study was to study the mutational profile of the ATP2C1 gene in Hong Kong Chinese patients with HHD. Methods Patients with the clinical diagnosis of HHD proven by skin biopsy were included in this study. Mutation analysis was performed in 17 Hong Kong Chinese patients with HHD. Results Ten mutations in the ATP2C1 gene were found. Six of these were novel mutations. The novel mutations included a donor splice site mutation (IVS22+1G>A); a missense mutation (c.1049A>T); two deletion mutations (c.185_188delAGTT and c.923_925delAAG); an acceptor splice site mutation (IVS21‐1G>C) and an insertion mutation (c.2454dupT). Conclusion The six novel mutations provide additions to the HHD mutation database. No hot‐spot mutation was found and high allelic heterogeneity was demonstrated in the Hong Kong Chinese patients.     

An Incompletely Penetrant Novel Mutation in COL7A1 Causes Epidermolysis Bullosa Pruriginosa and Dominant Dystrophic Epidermolysis Bullosa Phenotypes in an Extended Kindred

Abstract: Epidermolysis bullosa pruriginosa (EBP) is a rare subtype of dystrophic epidermolysis bullosa (DEB) characterized by intense pruritus, nodular or lichenoid lesions, and violaceous linear scarring, most prominently on the extensor extremities. Remarkably, identical mutations in COL7A1, which encodes an anchoring fibril protein present at the dermal–epidermal junction, can cause both DEB and EBP with either autosomal dominant or recessive inheritance. We present one family with both dystrophic and pruriginosa phenotypes of epidermolysis bullosa. The proband is a 19‐year‐old Caucasian woman who initially presented in childhood with lichenoid papules affecting her extensor limbs and intense pruritus consistent with EBP. Her maternal grandmother saw a dermatologist for similar skin lesions that developed without any known triggers at age 47 and mostly resolved spontaneously after approximately 10 years. The proband’s younger brother developed a small crop of pruritic papules on his elbows, dorsal hands, knees, and ankles at age 13. Her second cousin once removed, however, reported a mild blistering disease without pruritus consistent with DEB. Genetic sequencing of the kindred revealed a single dominant novel intron 47 splice site donor G>A mutation, c.4668 + 1 G>A, which we predict leads to exon skipping. Incomplete penetrance is confirmed in her clinically unaffected mother, who carries the same dominant mutation. The wide diversity of clinical phenotypes with one underlying genotype demonstrates that COL7A1 mutations are incompletely penetrant and strongly suggests that other genetic and environmental factors influence clinical presentation.     

Mutation L437P in the 2B domain of keratin 1 causes diffuse palmoplantar keratoderma in a Chinese pedigree

Diffuse palmoplantar keratoderma (DPPK) is an autosomal dominant genodermatosis characterized by uniform hyperkeratosis of the palm and sole epidermis. This disorder can be caused by mutations in the genes keratin 1 , keratin 9 , keratin 16 , desmoglein 1 and plakoglobin . Here we present a DPPK Chinese pedigree and identify the aetiology as a novel missense mutation, L437P, located in a highly conserved helix motif in domain 2B of KRT1. Functional analysis shows that overexpression of the L437P mutant in cultured cells leads to abnormal intermediate filament networks and filament aggregation. This gain-of-function mutation highlights the role of domain 2B in mediating filament assembly.

Conflicts of interest

The authors declare that they have no actual or potential conflicts of interest to disclose. Appropriate approval and procedures were used concerning human subjects.     

Two novel recessive mutations in KRT14 identified in a cohort of 21 Spanish families with epidermolysis bullosa simplex

Background Basal epidermolysis bullosa simplex (EBS) is a group of blistering genodermatoses mostly caused by mutations in the keratin genes, KRT5 and KRT14. Recessive mutations represent about 5% of all EBS mutations, being common and specific in populations with high consanguinity, where affected patients show severe phenotypes. Objectives To accomplish the first mutational analysis in patients of Spanish origin with EBS and to delineate a comprehensive genotype–phenotype correlation. Methods Twenty‐one EBS families were analysed. Immunofluorescence mapping at the dermoepidermal junction level was performed on skin biopsies from patients. Mutation screening of the entire coding sequences of KRT5 and KRT14 in genomic DNA was assessed by polymerase chain reaction and direct sequencing. Results KRT5 or KRT14 causative mutations were identified in 18 of the 21 EBS families. A total of 14 different mutations were disclosed, of which 12 were dominant missense mutations and two truncating recessive mutations. Five of the 14 mutations were novel including three dominant in KRT5 (p.V186E, p.T321P and p.A428T) and two recessive in KRT14 (p.K116X and p.K250RfsX8). The two patients with EBS carrying homozygous recessive mutations were affected by severe phenotypes and belonged to consanguineous families. All five families with the EBS Dowling–Meara subtype carried recurrent mutations affecting the highly conserved ends of the α‐helical rod domain of K5 and K14. The seven mutations associated with the localized EBS subtype were widely distributed along the KRT5 and KRT14 genes. Two families with mottled pigmentation carried the P25L mutation in KRT5, commonly associated with this subtype. Conclusions This study further confirms the genotype–phenotype correlation established for EBS in other ethnic groups, and is the first in a Mediterranean country (excluding Israel). This study adds two novel recessive mutations to the worldwide record to date, which includes a total of 14 mutations. As in previous reports, the recessive mutations resulted in a lack of keratin K14, giving rise to a generalized and severe presentation.     

弥漫性掌跖角化病一家系角蛋白9基因检测

目的：检测弥漫性掌跖角化病一家系中的KRT9基因突变情况。方法：提取该家系中3例患者和3名家系正常成员及100名健康对照的外周血DNA,采取PCR扩增KRT9基因序列,ABI PRISM-3700测序仪检测KRT9基因突变情况。结果：该家系中3例患者存在KRT9基因上第487位C>T突变,而该家系的正常成员及健康对照未检测到突变。结论：KRT9基因基因突变C487T可能与本家系弥漫性掌跖角化病发病有关。