Epidermolytic palmoplantar keratoderma cosegregates with a keratin 9 mutation in a pedigree with breast and ovarian cancer

Is punctate palmoplantar keratoderma type 1 associated with malignancy? A systematic review of the literature

BACKGROUND

An association between punctate palmoplantar keratoderma type 1 (PPPK1) and malignancy has been proposed for decades. Some authors suggest that individuals with PPPK1 should undergo screening for various types of malignancies while others caution that an association is not well-established. In this systematic review, we summarized and evaluated the current evidence for a possible association between PPPK1 and malignancy.

METHODS

The review was conducted along PRISMA guidelines. The search used Embase, MEDLINE, Scopus, and the Human Gene Mutation Database up to March 2022. All studies reporting on individuals with the diagnosis of PPPK1 with or without history of malignancy were included. Two authors screened for eligible studies, extracted predefined data, and performed a quality assessment.

RESULTS

Of 773 studies identified, 45 were included. Most studies were reports on single families (24 of 45 studies) or multiple families (10 of 45 studies). The number of index cases with PPPK1 across all included studies was 280, and when family members reported with PPPK1 were added, a total of 817 individuals were identified. Overall, 23 studies reported on individuals with PPPK1 with a history of malignancy, whereas 22 studies reported on individuals with PPPK1 without a history of malignancy. Although the extracted data were not considered to be of sufficient quality to synthesize and answer our research question, the review did not confirm an association between PPPK1 and malignancy.

CONCLUSION

This review shows that there is a lack of well-designed studies on this topic to conclude whether individuals with PPPK1 have an increased risk of malignancy. Based on the present literature, however, we could not confirm an association between PPPK1 and malignancy and find it highly questionable if patients with PPPK1 should be offered surveillance for malignancies.

Germline PALB2 Mutations in Cancers and Its Distinction From Somatic PALB2 Mutations in Breast Cancers

PALB2 is an important BRCAx candidate for familial breast cancers (FBC). PALB2 pathogenic variants (PVs) may not to conform to "two hit" paradigm. However, a recent study demonstrates that in the majority PALB2 germline mutant breast cancers, the loss of heterozygosity (LOH) and somatic point mutations are the "second hit." This study aimed to investigate the second hits in germline PALB2 mutations in breast cancers. We screened out 28 germline PALB2-mutation carriers among 480 familial cancer patients (including 143 FBC patients) in Geneplus database pool. Of the 143 patients with FBC, 10 had mono-allelic PALB2 germline mutations. All these germline PALB2 mutations were high-risk stop-gain, frameshift, or splicing mutations that concentrated in EX5-EX9 and might led to truncated proteins, severe functional defects and malignant phenotype. The hotspots were c.1057A[3 > 2] and c.3114-1G > A. Other mutations included c.389delA, c.2068C > T, c.2167_2168delAT, c.2629delT and c.2968G > T. Only one FBC patient has PALB2 somatic mutation and two patients had LOH of PALB2. All germline PALB2 mutations were high-risk mutations, whereas the somatic PALB2 mutations were moderate-risk missense mutations. We also distinguished PALB2 "novel mutations" from "reported mutations." In conclusion, germline PALB2 mutation should be put into the context of future screening.

Keratin 9 L164P mutation in a Chinese pedigree with epidermolytic palmoplantar keratoderma, cytokeratin analysis, and literature review

Background

Epidermolytic palmoplantar keratoderma (EPPK) is characterized by hyperkeratotic lesions on palms and soles. The disorder is caused by mutations of keratin 9 (KRT9) or KRT1 gene.

Methods

Epidermolytic palmoplantar keratoderma was diagnosed by physical examination and histopathological analysis in a five‐generation Chinese family. Mutation was screened by Sanger sequencing. The palmar expression of multiple cytokeratins were analyzed by tape‐stripping and Real‐time PCR. Literatures of EPPK with additional symptoms were reviewed.

Results

Affected family members showed diffuse palmoplantar keratosis, with knuckle pads, friction‐related lesions and a novel additional symptom of palmar constriction. A heterozygous mutation of c.T491C (p.L164P) of KRT9 was found within the helix initiation motif. The hydrophobic effect was decreased and the initiation of coiled‐coil conformation was delayed. The KRT16/KRT6 expression were significantly increased in the patients, especially on the right, indicating activation of stress‐response and wound‐healing cytokeratins. There were also increased KRT9/KRT2, unchanged KRT10/KRT1, and undetectable KRT14/KRT5 expression. The genetic and phenotypic heterogeneity of EPPK with additional symptoms were summarized by literature review.

Conclusion

The p.L164P mutation of KRT9 caused EPPK with a novel symptom of palmar constriction. The expression of multiple cytokeratins was altered in EPPK patients.

Epidermolytic hyperkeratosis: clinical update

Epidermolytic hyperkeratosis (EHK), earlier termed as bullous congenital ichthyosiform erythroderma is a skin disorder characterized as an autosomal dominant and rare disorder which has been observed to affect 1 in over 200,000 infants as a consequence of a significant mutation in the genes responsible for the keratin proteins, mostly keratin 1 and 10. The features present at birth include erythema and blistering. In adults, the hallmarks include hyperkeratosis, erosions, and blisters. The major symptoms including xerosis, pruritus, and painful fissuring lead not only to cosmetic problems but also stress, inferiority complex and other psychological conditions. While clinical inspection followed by confirmatory tests including histopathology and electron microscopic assessment is used for diagnosis, treatment modalities can be further improved for better diagnosis. This article reviews subtypes of ichthyosis, with a focus on EHK, genetics behind the disease, recently reported mutations, the existing diagnostics and treatments for the same and potential of new modalities in diagnosis/treatment.

Genetic Analysis of KRT9 Gene Revealed Previously Known Mutations and Genotype-Phenotype Correlations in Epidermolytic Palmoplantar Keratoderma

Epidermolytic palmoplantar keratoderma (EPPK, OMIM 144200) is an autosomal dominant inherited disease, clinically characterized by diffuse yellowish thickening of the skin on the palms and soles, usually with erythematous borders developing during the first weeks or months after birth. Pathogenesis of EPPK is determined by mutations in the keratin gene (KRT9). Thirty three mutations in the KRT9 gene from 100 EPPK families have been identified. Among these, 23 mutations are located in the 1A region (a mutation hot spot region), 7 are located in the 2B region, and the remaining 3 are synonymous mutations. In this study, three heterozygous mutations (p.N161S, p.R163W, and p.R163Q), located in regions of the gene encoding the conserved central a-helix rod domain, were detected in the KRT9 gene of the three large Chinese families. This study confirms that codon 163 (48 of 100 cases) is a hot spot mutation site for KRT9. Additional findings identified p.N161S (4%) and p.R163W (4%) as potential hot spot mutations for EPPK associated with knuckle pads, and p.R163Q (15 of 100 cases) as the hot spot mutation of EPPK not occurring in combination with knuckle pads. In conjunction with future studies, this research may help lay the foundation for genetics counseling, prenatal diagnosis and clinical treatment of EPPK.

Comparative genomics analyses of alpha-keratins reveal insights into evolutionary adaptation of marine mammals

Background

Diversity of hair in marine mammals was suggested as an evolutionary innovation to adapt aquatic environment, yet its genetic basis remained poorly explored. We scanned α-keratin genes, one major structural components of hair, in 16 genomes of mammalian species, including seven cetaceans, two pinnipeds, polar bear, manatee and five terrestrial species.

Results

Extensive gene loss and high pseudogenization rate of α-keratin genes were identified in cetaceans when compared to terrestrial artiodactylans (average number of α-keratins 37.29 vs. 58.33; pseudogenization rate 29.89% vs. 8.00%), especially of hair follicle-specific keratin genes (average pseudogenization rate in cetaceans of 43.88% relative to 3.80% artiodactylian average). Compared to toothed whale, the much more number of intact functional α-keratin genes was examined in the baleen whale that had specific keratinized baleen. In contrast, the number of keratin genes in pinnipeds, polar bear and manatee were comparable to those of their respective terrestrial relatives. Additionally, four keratin genes (K39, K9, K42, and K74) were found to be pseudogenes or lost uniquely in cetaceans and manatees.

Conclusions

Species-specific evolution of α-keratin gene family identified in the marine mammals might be responsible for their different hair characteristics. Increased gene loss and pseudogenization rate identified in cetacean lineages was likely to contribute to hair-less phenotype to adaptation for complete aquatic environment. However, the fully aquatic manatee still remained the comparable number of intact genes to its terrestrial relative, probably due to its perioral bristles and bristle-like hairs on the oral disk. By contrast, similar evolution pattern of α-keratin gene repertoire in the pinnipeds, polar bear and their terrestrial relatives was likely due to abundant hair to keep warm when they went ashore. Interestingly, some keratin genes were exclusively lost in cetaceans and manatees, likely as a result of convergent hair-loss phenotype to inhabit completely aquatic environment in both groups.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-017-0225-x) contains supplementary material, which is available to authorized users.

A novel mutation of KRT9 gene in a Chinese Han pedigree with epidermolytic palmoplantar keratoderma

BACKGROUND

Mutations of keratin 9 (KRT9) gene is a hot research area of epidermolytic palmoplantar keratoderma (EPPK).

AIMS

To identify the genes caused the EPPK of a Chinese family.

PATIENTS/METHODS

Three cases of lesions were collected for pathological examination. Genomic DNA was extracted from peripheral blood samples of six patients and five healthy individuals and 100 unrelated individuals. Polymerase chain reaction (PCR) was used to amplify exons 1 of KRT9 gene. PCR products were sequenced to identify potential mutations.

RESULTS

The lesion pathology of the proband and two ill relatives diagnosed EPPK. A new heterozygous missense mutation (488G>T) was identified in the 488 site of exon 1 of KRT9 gene in all six patients, which resulted in substitution of thymine for guanine, and substitution of leucine acid for arginine acid at position 163 of the KRT9 protein. The same mutation was not found in the five healthy individuals of the family and 100 unrelated individuals.

CONCLUSIONS

The new heterozygous missense mutation (488G>T) of KRT9 gene is probably the cause of EPPK in this Chinese family.

The human keratins: biology and pathology

The keratins are the typical intermediate filament proteins of epithelia, showing an outstanding degree of molecular diversity. Heteropolymeric filaments are formed by pairing of type I and type II molecules. In humans 54 functional keratin genes exist. They are expressed in highly specific patterns related to the epithelial type and stage of cellular differentiation. About half of all keratins—including numerous keratins characterized only recently—are restricted to the various compartments of hair follicles. As part of the epithelial cytoskeleton, keratins are important for the mechanical stability and integrity of epithelial cells and tissues. Moreover, some keratins also have regulatory functions and are involved in intracellular signaling pathways, e.g. protection from stress, wound healing, and apoptosis. Applying the new consensus nomenclature, this article summarizes, for all human keratins, their cell type and tissue distribution and their functional significance in relation to transgenic mouse models and human hereditary keratin diseases. Furthermore, since keratins also exhibit characteristic expression patterns in human tumors, several of them (notably K5, K7, K8/K18, K19, and K20) have great importance in immunohistochemical tumor diagnosis of carcinomas, in particular of unclear metastases and in precise classification and subtyping. Future research might open further fields of clinical application for this remarkable protein family.

The keratins and their disorders

Diseases caused by mutations in gene encoding keratin intermediate filaments (IF) are characterized by a loss of structural integrity in the cells expressing those keratins in vivo. This is manifested as cell fragility, compensatory epidermal hyperkeratosis, and keratin filament aggregation in some affected tissues. Keratin disorders are a novel molecular category including quite different phenotypes such as epidermolysis bullosa simplex (EBS), bullous congenital ichthyosiform erthroderma (BCIE), pachyonychia congenital (PC), steatocystoma multiplex, ichthyosis bullosa of Siemens (IBS), and white sponge nevus (WSN) of the orogenital mucosa.

Glial fibrillary acidic protein mutations in infantile, juvenile, and adult forms of Alexander disease

Alexander disease is a progressive, usually fatal neurological disorder defined by the widespread and abundant presence in astrocytes of protein aggregates called Rosenthal fibers. The disease most often occurs in infants younger than 2 years and has been labeled a leukodystrophy because of an accompanying severe myelin deficit in the frontal lobes. Later onset forms have also been recognized based on the presence of abundant Rosenthal fibers. In these cases, clinical signs and pathology can be quite different from the infantile form, raising the question whether they share the same underlying cause. Recently, we and others have found pathogenic, de novo missense mutations in the glial fibrillary acidic protein gene in most infantile patients examined and in a few later onset patients. To obtain further information about the role of glial fibrillary acidic protein mutations in Alexander disease, we analyzed 41 new patients and another 3 previously described clinically, including 18 later onset patients. Our results show that dominant missense glial fibrillary acidic protein mutations account for nearly all forms of this disorder. They also significantly expand the catalog of responsible mutations, verify the value of magnetic resonance imaging diagnosis, indicate an unexpected male predominance for the juvenile form, and provide insights into phenotype-genotype relations.

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.

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.

Identification of a locus for type I punctate palmoplantar keratoderma on chromosome 15q22-q24

BACKGROUND

The identification of the molecular basis of disorders of keratinisation has significantly advanced our understanding of skin biology, revealing new information on key structures in the skin, such as the intermediate filaments, desmosomes, and gap junctions. Among these disorders, there is an extraordinarily heterogeneous group known as palmoplantar keratodermas (PPK), for which only a few molecular defects have been described. A particular form of PPK, known as punctate PPK, has been described in a few large autosomal dominant pedigrees, but its genetic basis has yet to be identified.

AIM

Identification of the gene for punctate PPK.

METHODS

Clinical examination and linkage analysis in three families with punctate PPK.

RESULTS

A genomewide scan was performed on an extended autosomal dominant pedigree, and linkage to chromosome 15q22-q24 was identified. With the addition of two new families with the same phenotype, we confirmed the mapping of the locus for punctate PPK to a 9.98 cM interval, flanked by markers D15S534 and D15S818 (maximum two point lod score of 4.93 at theta = 0 for marker D15S988).

CONCLUSIONS

We report the clinical and genetic findings in three pedigrees with the punctate form of PPK. We have mapped a genetic locus for this phenotype to chromosome 15q22-q24, which indicates the identification of a new gene involved in skin integrity.

Keratin 9 gene mutations in five Korean families with epidermolytic palmoplantar keratoderma

Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant disease characterized clinically by localized palmoplantar thickening and histopathologically by granular degeneration of the epidermis. Recent molecular biological studies have revealed that EPPK is caused by mutations of the keratin 9 gene in sequences mainly encoding the highly conserved 1 A rod domain. Here we demonstrate a novel mutation of N160H (position 8 of the 1 A domain) and two other previously reported mutations, R162W and N160S, in five unrelated Korean families with EPPK. The three-dimensional structure of the 1 A domain of the related vimentin intermediate filament protein chain is now known. Based on its likely similarity to the keratin 9 chain, we predict that inappropriate amino acid substitutions in position 10 of 1 A will likely interfere with coiled-coil dimer stability, and those in position 8 will interfere with tetramer stability. Accordingly, these mutations compromise the structural integrity of the keratin intermediate filaments leading to the pathology of EPPK.

A novel mutation of keratin 9 in epidermolytic palmoplantar keratoderma combined with knuckle pads

Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominantly inherited disease. We studied a family from Shandong, China, having patients suffering from EPPK with a unique symptom-knuckle pads. We noticed that both the hyperkeratosis and knuckle pads in the Chinese family were friction-related. Candidate gene analysis was carried out using linkage analysis and direct sequencing. A novel L160F mutation in keratin 9 was found, and its effects on the secondary structure of keratin 9 were studied. We predict that the L160F mutation is also responsible for the knuckle pads in the family. Our study provides a new clue for the study of the function of keratin 9.

A keratin 9 Gene mutation (Asn160Ser) in a Japanese patient with epidermolytic palmoplantar keratoderma

We described a 5-year-old Japanese girl with epidermolytic palmoplantar keratoderma and examined her for a keratin 9 gene mutation. Physical examination disclosed diffuse yellowish hyperkeratosis with an erythematous border limited strictly to the palms and soles. Histological examination revealed hyperkeratosis with vacuolar degeneration in the spinous and granular layers of the epidermis. Sequence analysis demonstrated an A to G transition at the middle position of codon 160 in the 1A domain of the keratin 9 gene. The amino acid at codon 160 was deduced to have changed from asparagine (Asn) to serine (Ser). This is the first case with an Asn160Ser mutation in a Japanese. The substitution of Ser for Asn at codon 160 of the keratin 9 gene is assumed to be fatal for keratin filament assembly regardless of race or ethnicity.

The molecular basis of hereditary palmoplantar keratodermas

In recent years, the gene defects causing many types of hereditary palmoplantar keratoderma have been discovered. These genes encode a variety of proteins involved in the terminal differentiation of keratinocytes and the formation of the cornified cell envelope. In this article, we review the molecular defects underlying various palmoplantar keratodermas with particular attention to the role of these molecules in the terminal differentiation of palmoplantar epidermis. Of the proteins involved in keratodermas, loricrin, keratins, and desmosomal proteins provide the protein structure of the cornified cell envelope. Connexins form intercellular gap junctions, which regulate ionic calcium signals necessary for the expression of the proteins that form the cornified cell envelope. Cathepsins likely mediate enzymatic processes necessary for the formation and dissolution of the cornified cell envelope. The clinical phenotypes produced by various mutations affecting these proteins are discussed vis-à-vis data from genetic, cellular, and molecular experiments.

GFAP mutations in Alexander disease

Alexander disease is a rare but often fatal disease of the central nervous system. Infantile, juvenile and adult forms have been described that present with different clinical signs, but are unified by the characteristic presence in astrocytes of Rosenthal fibers-protein aggregates that contain glial fibrillary acidic protein (GFAP) and small stress proteins. The chance discovery that mice expressing a human GFAP transgene formed abundant Rosenthal fibers suggested that mutations in the GFAP gene are a cause of Alexander disease. Sequencing results from several laboratories have indeed now identified GFAP coding mutations in most cases of the disease, including both the infantile and juvenile forms. These mutations have been found in the 1A, 2A and 2B segments of the conserved central rod domain of GFAP, and also in the variable tail region. All changes detected are heterozygous missense mutations, and none has been found in any parent of a patient that has been tested. This indicates that most cases of Alexander disease arise through de novo, dominant, GFAP mutations. Many of these mutations are homologous to ones described in other intermediate filament diseases. These other diseases have been attributed to a dominant loss of function, as the intermediate filament network is usually disrupted and a similar phenotype is observed in mice in which the corresponding intermediate filament gene has been inactivated. However, astrocytes of Alexander disease patients have normal appearing intermediate filaments, and GFAP null mice do not display the symptoms or pathology of Alexander disease. Thus, Alexander disease likely results from a dominant gain of function. Drawing upon the homology of many of the Alexander disease mutations to those found in other intermediate filament diseases, it is suggested that the gain of function is due to a partial block of filament assembly that leads to accumulation of an intermediate that participates in toxic interactions.

Diagnosis and confirmation of epidermolytic palmoplantar keratoderma by the identification of mutations in keratin 9 using denaturing high-performance liquid chromatography

BACKGROUND

Epidermolytic palmoplantar keratoderma (EPPK) is one of a number of disorders characterized by diffuse thickening of palm and sole skin. Although EPPK is not a life-threatening condition, palmoplantar keratoderma can be associated with cancer and heart disease and therefore differential diagnosis is important so that adequate surveillance can be provided for the more serious conditions. Most cases of EPPK are caused by mutations in the gene encoding the palm- and sole-specific keratin 9 (K9), and this provides an option for molecular diagnosis of this condition.

OBJECTIVES

To identify the molecular basis of diffuse palmoplantar keratoderma in four British families.

METHODS

Denaturing high-performance liquid chromatography (dHPLC) and DNA sequencing were used to screen exon 1 of the k9 gene for sequence variations.

RESULTS

The dHPLC profiles obtained from individuals with EPPK differed from control samples, indicating sequence variations within the fragment analysed. The profiles varied between families, suggesting that underlying mutations were different for each family; this was confirmed by DNA sequencing. In three cases previously reported mutations were found that resulted in the change of methionine156 to valine and arginine162 to either tryptophan or glutamine. A novel mutation was identified in a fourth family that changed valine170 to methionine. dHPLC was used to screen control samples for this sequence variation and confirmed that it was not a common polymorphism.

CONCLUSIONS

These results confirm the diagnosis of EPPK in these families and underline the usefulness of dHPLC as a method of screening samples for heterozygous mutations.

New mutations in keratin 1 that cause bullous congenital ichthyosiform erythroderma and keratin 2e that cause ichthyosis bullosa of Siemens

The intermediate filaments of epithelial cells are formed by keratins, a family of structurally related proteins, which are expressed in pairs of acidic (type I) and basic (type II) polypeptides in a tissue- and differentiation-specific manner. Mutations in the genes encoding several keratins have been implicated in the pathogenesis of diseases of keratinization. We report molecular analysis of two patients with the rare autosomal dominant disorders bullous congenital ichthyosiform erythroderma (BCIE) and ichthyosis bullosa of Siemens (IBS). Previous studies have shown that these genodermatoses are due to mutations in the KRT1 and KRT2E genes, respectively. We report a new amino acid substitution mutation in codon 155 of KRT1 (valine to aspartic acid) in the conserved H1 domain of the protein in the patient with BCIE. We also report a novel amino acid substitution mutation in codon 192 of KRT2E (asparagine to lysine) in the conserved 1A helix initiation peptide of the protein in the patient with IBS. Our results demonstrate that these mutations are deleterious to keratin filament network stability and lead to specific clinical inherited disorders of keratinization.

Genetic correction of inherited epidermal disorders

Genetic correction of monogenic human skin disorders represents a potentially effective molecular therapy for severe diseases in which current therapy is only palliative. The stratified epithelium of the epidermis represents the tissue location with the largest number of genetic skin diseases yet characterized. Specific requirements of successful gene delivery in this setting include correct targeting within tissue, durability, and a lack of immunogenecity. Progress toward this goal has advanced from identification of disease genes to reintroduction of wild-type genes to patient cell lines and primary cells in vitro. This initial work has been extended to gene-based correction of diseased tissue regenerated in vivo in the form of human patient skin xenografts on immune-deficient mice. Efforts in this human tissue model have laid the foundation for future efforts to extend this progress toward ex vivo cutaneous gene therapy trials in humans.

Epidermolytic palmoplantar keratoderma in a Hispanic kindred resulting from a mutation in the keratin 9 gene

Epidermolytic palmoplantar keratoderma (EPPK) is a localized keratinization disorder caused by mutations in the highly conserved coil 1A domain of the keratin 9 gene, KRT9. We present a Hispanic pedigree spanning three generations, with affected individuals in all generations. Using polymerase chain reaction amplification and direct sequencing we demonstrated a previously reported missense mutation in KRT9, which is expressed almost exclusively in the skin of palms and soles. The C-->T missense mutation R162W changes a basic amino acid (arginine) to a neutral amino acid (tryptophan). We describe this mutation in a Hispanic pedigree with EPPK for the first time, extending the finding of this mutation in other genetic backgrounds, and demonstrating the prevalence of this mutation in diverse populations.

A novel asparagine-->aspartic acid mutation in the rod 1A domain in keratin 2e in a Japanese family with ichthyosis bullosa of Siemens

Ichthyosis bullosa of Siemens is a unique type of congenital ichthyosis characterized by mild hyperkeratosis over the flexural areas and blister formation after mechanical trauma and superficial denuded areas in the hyperkeratotic skin. Recently, mutations in the helix initiation or termination motifs of keratin 2e (KRT2E) have been described in ichthyosis bullosa of Siemens patients. The majority of the mutations reported to date lie in the 2B region. We report a novel amino acid substitution mutation (asparagine-->aspartic acid) in codon 192 at the conserved 1A helix initiation site of the rod domain of KRT2E in a Japanese family with ichthyosis bullosa of Siemens. Our data indicate aspartic acid substitution in codon 192 in the 1A helix initiation site is deleterious to keratin filament network integrity and leads to ichthyosis bullosa of Siemens phenotype.

Gene therapy and dermatology: more than just skin deep

BACKGROUND

Recent advances in the molecular characterization of dermatologic disease have substantively augmented the understanding of the pathogenetic processes underlying disorders of the skin. This new knowledge coupled with progress in gene delivery technologies has paved the way for introducing cutaneous gene therapy into the dermatologic therapeutic armamentorium.

OBJECTIVE

This review article includes an overview of the current strategies for delivery of gene therapy with an emphasis on the potential role of cutaneous gene delivery in the treatment of skin and systemic diseases.

CONCLUSIONS

Accessibility for gene delivery, clinical evaluation, and topical modulation of gene expression render the skin a very attractive tissue for therapeutic gene delivery. However, there are several key hurdles to be overcome before cutaneous gene therapy becomes a viable clinical option. These include difficulties in inducing sustained expression of the desired gene in vivo, the challenge of targeting genes to long-lived stem cells, and the difficulty in achieving specific and uniform transfer to different compartments of the skin. However, these problems are not insurmountable and will likely be resolved in conjunction with ongoing advances in delineating gene expression profiles and other molecular properties of the skin, strategies for stem cell isolation, and improved approaches to regulating gene delivery and expression. These advances should create the framework for translating the enormous potential of cutaneous gene therapy into the clinical arena and, thereby, substantively improving the management of both cutaneous and systemic disease.

Regulation of keratin 9 in nonpalmoplantar keratinocytes by palmoplantar fibroblasts through epithelial-mesenchymal interactions

Palms and soles differ from other body sites in terms of clinical and histologic appearance, response to mechanical stress, and the distribution of keratin 9. Because keratin 9 is exclusively expressed in the palmoplantar suprabasal keratinocyte layers, it is considered a differentiation marker of palms and soles. We studied palmoplantar mesenchymal influences on keratin 9 induction in nonpalmoplantar epidermis. Although palmoplantar keratinocytes when cultured alone continued to express keratin 9 mRNA in 12 (100%) of 12 cultures, nonpalmoplantar keratinocytes did not express it in 16 of 17 cultures. Although nonpalmoplantar keratinocytes did not express keratin 9 mRNA when cultured with nonpalmoplantar fibroblasts, they did express it within 2 h in cocultures with palmoplantar fibroblasts derived from papillary dermis. Grafting of these coculture sheets on severe combined immunodeficient mice resulted in an epidermis, which histologically showed hyperkeratosis and acanthosis and immunohistochemically expressed keratin 9. Furthermore, pure epidermal sheets from nonpalmoplantar skin grafted on the human sole wounds due to burn, injury, and the resection of acral lentiginous melanoma, demonstrated adoption of palmoplantar phenotype and expressed keratin 9. Our report indicates extrinsic keratin 9 regulation by signals from dermal fibroblasts. This is also the first to suggest the possibility of treating palmoplantar wounds with nonpalmoplantar epidermis, which is much easier to obtain and harvest.

Demonstration of the pathogenic effect of point mutated keratin 9 in vivo

A wild type keratin 9 (K9) cDNA and a point mutated keratin 9 cDNA were injected subcutaneously into mouse skin. The hemagglutinin tag staining of the wild type K9 cDNA injected specimens mainly showed a homogeneous pattern, whereas the point mutated K9 cDNA injected specimens mainly showed a granular pattern in the suprabasal cells. Double staining of K9 and the endogenous keratin revealed the incorporation of de novo synthesized K9 into the keratin network. These results demonstrate that (1) a naked DNA transfection into mouse skin can detect the pathogenic changes of point mutated keratin in vivo and (2) the keratin 9 mutation disrupts the keratin network formation in the suprabasal cells in vivo.

Cutaneous manifestations of cancer

The appearance of skin lesions in patients with occult or obvious malignancy may be of extreme value in the detection and management of cancer because the skin is readily accessible to examination and biopsy. Examination of the skin of our patients can provide important insights into underlying malignant processes or possible complications from cancer treatment. The range of cutaneous abnormalities is wide, and include cutaneous paraneoplastic syndromes such as xanthomas, acanthosis nigricans, carcinoid syndrome, unusual erythematous eruptions such as erythema gyratum repens, and a number of genetic syndromes associated with malignancies and inherited dermatoses.

The palmoplantar keratodermas: much more than palms and soles

The inherited palmoplantar keratodermas (PPKs) are a diverse and often clinically confusing branch of the genetic skin diseases. As the name suggests, the lesions of PPK primarily affect the palms and soles of the feet, although a number of the PPKs are also associated with a genetic predisposition to other conditions, including cancer, hearing loss and heart failure. The mapping and identification of genes that underlie the PPKs reveal new insights into the biological interactions of the structural components of the palmoplantar epidermis and further our understanding of epidermal disease. More significantly, by genetically characterizing the PPKs, genes that have a role in life-threatening disorders might also be identified.

Epidermolytic palmoplantar keratoderma due to a novel type of keratin mutation, a 3-bp insertion in the keratin 9 helix termination motif

Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant genodermatosis characterized by diffuse keratoderma, typically with an erythematous border. Histologically, palmoplantar epidermis shows suprabasal cytolysis and ultrastructurally, tonofilament aggregation with overlying epidermolytic hyperkeratosis. Mutations in the KRT9 gene, encoding keratin 9 (K9), a cytoskeletal protein expressed exclusively in suprabasal keratinocytes of palmoplantar epidermis, have been reported to cause EPPK. To date, all KRT9 defects reported in EPPK have been missense mutations in exon 1, which encodes the start of the alpha-helical rod domain. However, based on studies of other keratin disorders, it was postulated that mutations at the other end of the rod domain might also produce the EPPK phenotype. Here, we report the first mutation in the 2B domain of KRT9, 1362ins3, leading to an insertion of histidine in the helix termination motif of the K9 polypeptide. Insertional mutations have not been previously described in keratins. The phenotype of this case is similar to EPPK caused by 1A domain mutations, demonstrating that mutations in either of the helix boundary motif sequences of K9 are detrimental to keratin function and keratinocyte structure.

Mutations in keratin K9 in kindreds with epidermolytic palmoplantar keratoderma and epidemiology in Northern Ireland

Epidermolytic palmoplantar keratoderma (EPPK, MIM #144200) is an autosomal dominant disorder in which hyperkeratosis confined to the palms and soles is characterized histologically by cytolysis of suprabasal keratinocytes. Mutations in the keratin 9 gene (KRT9), a type 1 keratin expressed exclusively in the suprabasal keratinocytes of palmoplantar epidermis, have previously been demonstrated in this disorder. Here, we have studied four Northern Irish kindreds presenting with EPPK. By direct sequencing of polymerase chain reaction products, heterozygous missense mutations in exon 1 of KRT9 were detected in all the families. These included a novel mutation M156T; as well as M156V in two kindreds; and R162Q in the remaining family. All mutations were confirmed by reverse strand sequencing and restriction enzyme analysis. The point prevalence of EPPK in Northern Ireland was found to be 4.4 per 100,000. To date, all reported EPPK mutations occur in the helix initiation motif at the start of the central coiled-coil rod domain of K9.

Specialized keratin expression pattern in human ridged skin as an adaptation to high physical stress

We have analysed the expression of keratins in the epidermis of normal human palm and sole skin (ridged skin) using immunohistochemistry and in situ hybridization. The epidermis of human ridged skin expresses a more complex pattern of keratins than thin skin, which is probably due to the greater stress that ridged skin has to withstand. In addition to keratin K9, we document specific expression patterns of keratins K6, K16 and K17 which are suggestive of regional adaptations of this epidermis to a high cell turnover rate. In particular, the sequestered location of nests of K17-positive cells at the bottom of the deep primary epidermal ridges supports the notion of functional heterogeneity of basal cells and suggests that the K17-positive sites may include stem cells. Expression of K6 and K16 in some basal and most suprabasal keratinocytes is compatible with a constitutively high proliferative activity of normal ridged epidermis, but may also reflect different physical properties of the suprabasal cells, in contrast with regions expressing K9. The distinct labelling patterns observed in primary and secondary epidermal ridges as well as epidermal layers above dermal papillae suggest the existence of local microenvironmental niches leading to differences in keratinocyte differentiation.

Genomic organization and fine mapping of the keratin 2e gene (KRT2E): K2e V1 domain polymorphism and novel mutations in ichthyosis bullosa of Siemens

We and others have previously shown that ichthyosis bullosa of Siemens, an autosomal dominant disorder characterized by epidermal thickening and blistering, is caused by mutations in the late-differentiation keratin K2e. Here, we have determined the genomic organization and complete sequence of the KRT2E gene, which consists of nine exons, spanning 7634 bp of DNA. The gene was mapped by high-resolution radiation-hybrid mapping to the interval between microsatellite markers D12S368 and CHLC.GATA11B02.1112. Several intragenic polymorphisms were detected, including an 18 bp duplication in exon 1, corresponding to the V1 domain of the K2e polypeptide. Genomic polymerase chain reaction conditions were optimized for all exons, and two novel mutations, N192Y in the 1A domain and E482K in the 2B domain of K2e, were found in ichthyosis bullosa of Siemens families. Mutations were excluded from 50 normal unrelated individuals by restriction analysis. These results emphasize that mutations in K2e underlie ichthyosis bullosa of Siemens and provide a comprehensive mutation detection strategy for ongoing studies of keratinizing disorders.

Gene for arrhythmogenic right ventricular cardiomyopathy with diffuse nonepidermolytic palmoplantar keratoderma and woolly hair (Naxos disease) maps to 17q21

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a heart muscle disease of unknown etiology that causes arrhythmias, heart failure, and sudden death. Diagnosis can be difficult, and this hampers investigation of its molecular basis. Forms of ARVC in which gene penetrance and disease expression are greater should facilitate genetic study. We undertook a clinical and genetic investigation of Naxos disease, originally described by Protonotarios in 1986. This disease constitutes the triad of ARVC, diffuse nonepidermolytic palmoplantar keratoderma, and woolly hair.

METHODS AND RESULTS

We evaluated the population of Naxos, Greece, to identify probands, which was followed by family screening. Twenty-one affected persons from 9 families of 150 persons were identified. Linkage analysis was performed with microsatellite markers. The disease locus mapped to 17q21. A peak 2-point LOD score of 3.62 at theta=0.0 was found with a marker within intron 4 of the keratin 9 gene, a member of the type I (acidic) keratin family. A preserved homozygous disease haplotype was identified. Haplotype analysis delimited the disease interval.

CONCLUSIONS

Hair and skin abnormalities were found to be reliable markers of subsequent heart disease. This suggests the presence of a single mutant gene with novel cardiac, skin, and hair function or two or more tightly linked disease genes. Recessive inheritance of Naxos disease and a founder effect were demonstrated. Identification of a fully informative genetic marker linked to the disease and uncommon in the background population may be of use as a test to identify disease gene carriers.

Hereditary epidermolytic palmoplantar keratoderma (Vörner type) in a family with Ehlers-Danlos syndrome

We describe a kindred in whom epidermolytic palmoplantar keratoderma occurred in association with Ehlers-Danlos syndrome type III (benign hypermobility syndrome). This kindred consisted of 27 members of four generations, 14 of whom had palmoplantar keratoderma (PPK). Of those who had palmoplantar keratoderma, 6 had Ehlers-Danlos type III (EDS II). The proband presented with diffuse, symmetrical hyperkeratotic plaques that were yellow and sharply demarcated, covering the entire palms and soles, in addition to marked large and small joint flexibility and skin hyperextensibility. A biopsy specimen from the palm revealed features of epidermolytic hyperkeratosis with acanthosis. To our knowledge, this is the first report of PPK in a family with Ehlers-Danlos syndrome. Linkage analysis of these two clinical traits showed that the genes responsible for PPK and EDS III are not closely linked, and therefore are not immediately adjacent. However, linkage at greater genetic distances could not be excluded.

The inherited palmoplantar keratodermas

The inherited palmoplantar keratodermas (PPK) constitute a complex heterogeneous group of genodermatoses, which are difficult to classify clinically. The application of modern molecular biology techniques are leading to an increased understanding of the genetic bases of these disorders and are paving the way towards a classification based upon molecular pathology. We review the recent research advances in this field and the implications for development of novel approaches to disease management.

A novel mutation of a leucine residue in coil 1A of keratin 9 in epidermolytic palmoplantar keratoderma

Keratin 9 mutation was examined in a Japanese kindred of epidermolytic palmoplantar keratoderma (EPPK), which is a dominantly inherited autosomal disorder of keratinization characterized by diffuse thickening of the palms and soles and by epidermolytic hyperkeratosis histologically. We report herein a novel mutation, a C --> G transversion at nucleotide position 541 that converts a leucine residue (CTC) to a valine (GTC) at codon 159. As in all other reported cases of keratin 9 mutation in EPPK, this mutation lies within the highly conserved coil 1A of the rod domain, which is considered to play a role in the correct alignment of the coiled-coil molecules.

Keith R. Porter Lecture, 1996. Of mice and men: genetic disorders of the cytoskeleton

Since the time when I was a postdoctoral fellow under the supervision of Dr. Howard Green, then at the Massachusetts Institute of Technology, I have been interested in understanding the molecular mechanisms underlying growth, differentiation, and development in the mammalian ectoderm. The ectoderm gives rise to epidermal keratinocytes and to neurons, which are the only two cell types of the body that devote most of their protein-synthesizing machinery to developing an elaborate cytoskeletal architecture composed of 10-nm intermediate filaments (IFs). Our interest is in understanding the architecture of the cytoskeleton in keratinocytes and in neurons, and in elucidating how perturbations in this architecture can lead to degenerative diseases of the skin and the nervous system. I will concentrate on the intermediate filament network of the skin and its associated genetic disorders, since this has been a long-standing interest of my laboratory at the University of Chicago.

Genetic studies of syndromes with severe periodontitis and palmoplantar hyperkeratosis

The Papillon-Lefèvre and Haim Munk syndromes are characterized by the presence of both palmoplantar hyperkeratosis (PPK) and severe early onset periodontitis. It is the early onset periodontal disease component that distinguishes these from other more common forms of PPK. It has been proposed that the periodontal disease component may be a casual association in individuals with PPK. Genetic syndromes with palmoplantar keratosis and severe ealry onset periodontitis may be due to specific bacterial infections in individuals with PPK. Recently, keratin gene mutations have been identified in several conditions typified by palmoplantar keratosis. The present study sought to test the hypothesis that a keratin gene defect similar to those previously identified in other PPK conditions is responsible for the Haim Munk and the Papillon. Lefèvre syndromes. We have performed genetic linkage studies to test for linkage between polymorphic DNA loci within 2 cytokeratin gene families and the disease phenotype in Haim Munk syndrome and Papillon-Lefèvre syndrome. Families with individuals segregating for the Haim Munk syndrome and the Papillon-Lefèvre syndrome were examined to determine disease status, and genotyped for microsatellite DNA markers closely linked to the acidic (type I) and the basic (type II) cytokeratin genes on chromosomes 12 and 17. Genotype data were evaluated for microsatellite allele homozygosity in affected individuals. Results of these preliminary genetic studies suggest that the gene defect in Haim Munk syndrome is not due to a gene defect in either the type I or the type II keratin gene clusters. These findings suggest that Haim Munk syndrome may be genetically distinct from other more common forms of PPK that have been linked to the cytokeratin gene families, and suggest that mutations in genes other than keratin genes are responsible. Additional family studies are needed to confirm these preliminary findings.

Protein chains in hair and epidermal keratin IF: structural features and spatial arrangements

Over the past decade the progress made in characterising the structural hierarchy of both the hard and the epidermal keratin intermediate filaments has exceeded all expectations. The origin of much of this progress can be traced back to the quantity of amino acid sequence data that became available in the early/mid 1980s, and their interpretation in terms of a heterodimeric molecular structure. Subdomains were subsequently identified in both the rod and terminal domains, and now the roles of most of these have been determined in principle, if not yet fully in detail. TEM and STEM, together with very revealing crosslinking analyses have also allowed details to be determined of the mechanism by which molecules assemble into oligomers and oligomers into IF. It remains for the three-dimensional packing of keratin molecules in the IF to be elucidated, but even here progress is being made. A particularly exciting development over the last two or three years has been the establishment of the link between keratinopathies and single point nucleotide mutations in keratin genes. Furthermore, the clustering of mutation sites in regions involved in a key structural mode of molecular aggregation has provided, for the first time, an understanding of keratin diseases at the molecular level.

Exclusion of allelism of Noonan syndrome and neurofibromatosis-type 1 in a large family with Noonan syndrome-neurofibromatosis association

A large four-generation family with Noonan syndrome (NS) and neurofibromatosis-type 1 (NF1) was studied for clinical association between the two diseases and for linkage analysis with polymorphic DNA markers of the NF1 region in 17q11.2. Nonrandom segregation between NS and NF1 phenotypes was observed. Neurofibromatosis was tightly linked to NF1 markers, whereas Noonan syndrome was found not be allelic to NF1. These results suggest that two mutations at two independent but closely linked loci are the cause of neurofibromatosis-Noonan syndrome (NF-NS) association in this family.

JSID Tanioku Memorial Lecture 1996. Genetic disorders of keratins and their associated proteins

It has recently been demonstrated that genetic defects in keratin genes cause a number of different skin disorders, including epidermolysis bullosa simplex (EBS), epidermolytic hyperkeratosis (EH), the EH form of epidermal nevi, epidermolytic and non-epidermolytic forms of palmoplantar keratoderma (EPPK and PPK) and pachyonychia congenita (PC). In this review, I describe the research that led to this discovery.