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

Mutation p.Arg127Pro in the 1A Domain of KRT16 Causes Pachyonychia Congenita in Chinese Patient: A Case Report of PC Associated with Acral Melanoma

Pachyonychia congenita (PC) is a group of rare hereditary disorders, characterised by hypertrophic nails and palmoplantar keratoderma (PPK), particularly localised to the pressure areas of the feet. At a molecular level, it is caused by mutations in genes encoding KRT6A, KRT6B, KRT6C, KRT16, or KRT17. To identify the underlying gene mutation in a Chinese family with PC presenting with disabling palmoplantar keratoderma and subsequent associated acral melanoma. Genomic DNA was extracted from peripheral blood samples of three available individuals in the Chinese family, which included the patient and his two unaffected sisters. The index patient presented with severe palmoplantar keratoderma as well as a newly diagnosed acral malignant melanoma (MM). Whole-exome sequencing (WES) was carried out with amplification of exon 1 of KRT16 by polymerase chain reaction (PCR). PCR products were then sequenced to identify potential mutations. We identified the proline substitution mutation p.Arg127Pro (c.380G>C) in our patient's 1A domain of KRT16. The same mutation was not found in his sisters or unrelated healthy controls. The mutation (p.Arg127Pro (c.380G>C)) in KRT16 has been reported in Dutch patients with PC. However, it is the first such report of a patient with a PC of Chinese origin. In addition, the acral MM occurred under the background of genetic PPK caused by KRT16 mutation in this patient.

KRT17 from skin cells with high glucose stimulation promotes keratinocytes proliferation and migration

Impaired diabetic wound healing is an important issue in diabetic complications. Proliferation and migration of keratinocytes are major processes of skin wound repair after injury. However, hyperkeratosis can affect the speed of wound healing. Based on the results of preliminary experiments on increased KRT17 expression after high glucose stimulation of human skin tissue cells, a cell model of human immortalized keratinocyte (HaCaT) stimulation with different concentrations of KRT17 was established in vitro, and the promotion in cell proliferation and migration were discovered. KRT17 silencing promoted diabetic wound healing in the db/db diabetic wound model. Transcriptome sequencing (RNA-seq) was performed on HaCaT cells after KRT17 stimulation, and analysis showed significant enrichment in the PI3K-AKT signaling pathway, in which the regulation of cell c-MYB mRNA, a key molecule regulating cell proliferation and migration, was significantly upregulated. In vitro assays showed increased c-MYB expression and enhanced pAKT activity after HaCaT cell stimulation by KRT17. We speculate that KRT17 is upregulated under high glucose and promotes keratinocyte proliferation and migration caused hyperkeratosis, through the c-MYB/PI3K-AKT pathway, contributing to delayed wound healing.

A KRT6A and a Novel KRT16 Gene Mutations in Chinese Patients with Pachyonychia Congenita

BACKGROUND

Pachyonychia congenita (PC) is a rare, autosomal dominant genodermatosis characterized by palmoplantar keratoderma, nail dystrophy, cystic lesions, follicular hyperkeratosis, mucosal leukokeratoses, hyperhidrosis, hoarseness, and, rarely, natal teeth. Five keratin genes, KRT6A, KRT6B, KRT6C, KRT16 and KRT17, have been found to be associated with PC.

METHODS

Using polymerase chain reaction and Sanger sequencing techniques, the purpose of the present study was to investigate the clinical features associated with PC and discover disease-associated variants. The KRT6A, KRT16, KRT17, and KRT6B exonic and flanking region sequences were amplified and directly sequenced to detect mutations.

RESULTS

Across two independent instances of PC, we identified a previously reported c.1393T>C (p.Tyr465His) mutation in exon 7 of KRT6A, and a novel c.1237G>C (p.Glu413Gln) heterozygous missense mutation in exon 6 of the KRT16 gene.

CONCLUSION

Through phenotype-genotype analysis among PC pedigrees, confirmed diagnoses of PC-K6a and PC-K16 were made in the two patients who presented with symptoms of PC. A new pathogenic mutation site in PC-K16 was potentially discovered.

Molecular epidemiology of pachyonychia congenita in the Israeli population

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant disorder featuring palmoplantar keratoderma, nail dystrophy, oral leucokeratosis, pilosebaceous cysts and natal teeth. PC results from dominant mutations in one of five genes (KRT6A, KRT6B, KRT6C, KRT16, KRT17) encoding keratin proteins.

AIM

To delineate the clinical and genetic features of PC in a series of Israeli patients.

METHODS

We used direct sequencing of genomic DNA, and also used cDNA sequencing where applicable.

RESULTS

We collected clinical information and molecular data in a cohort of Israeli families diagnosed with PC (n = 16). Most of the patients were Ashkenazi Jews and had a family history of PC. The most common clinical findings were painful focal plantar keratoderma (94%) accompanied by nail dystrophy (81%), pilosebaceous cysts (31%) and prenatal/natal teeth (13%). In contrast to the high prevalence of KRT6A mutations in other populations, we found that KRT16 mutations were the most common type among Israeli patients with PC (56%). Most (77%) of the Israeli patients with PC with KRT16 mutation carried the same variant (c.380G>A; p.R127H) and shared the same haplotype around the KRT16 locus, suggestive of a founder effect.

CONCLUSION

The data gleaned from this study emphasizes the importance of population-specific tailored diagnostic strategies.

Ultrasound Morphologic Features of Steatocystoma Multiplex With Clinical Correlation

The ultrasound features of 87 steatocytoma multiplex (SCM) lesions detected in 9 patients are reported. Steatocytoma multiplex is a hamartomatous condition derived from the pilosebaceous duct junction that generates multiple cutaneous cystic lesions. It appeared as clusters of well-defined hypoechoic nodules with mild posterior enhancement in 100% of cases, with both dermal and subcutaneous locations in 67%. No calcification foci were detected within or at the periphery of the lesions. Fifty-six percent of the cases showed signs of hypervascularity in the edge of the nodules, and 44% of the lesions were associated with another dermatologic condition, most frequent being hidradenitis suppurativa (75%), followed by vellus hair cysts (25%). Steatocytoma multiplex shows ultrasound features that allow discrimination from other common cutaneous entities.

Palatal steatocystoma simplex-a rare oral finding at an even rarer location

Steatocystoma is a rare, benign cyst that mostly originates from a dermal sebaceous gland. It can be divided into steatocystoma multiplex—with multiple locations—and steatocystoma simplex occurring at a single site. The lesion is mostly located on the skin but can be found on other locations as well. This is the first case report of steatocystoma simplex that was found in the palate of a 37-year-old male. After resection with small safety margins and local wound dressing, no recurrence was detected during a follow-up of 1.5 years.

Pathophysiology of pachyonychia congenita-associated palmoplantar keratoderma: new insights into skin epithelial homeostasis and avenues for treatment

BACKGROUND

Pachyonychia congenita (PC), a rare genodermatosis, primarily affects ectoderm-derived epithelial appendages and typically includes oral leukokeratosis, nail dystrophy and very painful palmoplantar keratoderma (PPK). PC dramatically impacts quality of life although it does not affect lifespan. PC can arise from mutations in any of the wound-repair-associated keratin genes KRT6A, KRT6B, KRT6C, KRT16 or KRT17. There is no cure for this condition, and current treatment options for PC symptoms are limited and palliative in nature.

OBJECTIVES

This review focuses on recent progress made towards understanding the pathophysiology of PPK lesions, the most prevalent and debilitating of all PC symptoms.

METHODS

We reviewed the relevant literature with a particular focus on the Krt16 null mouse, which spontaneously develops footpad lesions that mimic several aspects of PC-associated PPK.

RESULTS

There are three main stages of progression of PPK-like lesions in Krt16 null mice. Ahead of lesion onset, keratinocytes in the palmoplantar (footpad) skin exhibit specific defects in terminal differentiation, including loss of Krt9 expression. At the time of PPK onset, there is elevated oxidative stress and hypoactive Keap1-Nrf2 signalling. During active PPK, there is a profound defect in the ability of the epidermis to maintain or return to normal homeostasis.

CONCLUSIONS

The progress made suggests new avenues to explore for the treatment of PC-based PPK and deepens our understanding of the mechanisms controlling skin tissue homeostasis. What's already known about this topic? Pachyonychia congenita (PC) is a rare genodermatosis caused by mutations in KRT6A, KRT6B, KRT6C, KRT16 and KRT17, which are normally expressed in skin appendages and induced following injury. Individuals with PC present with multiple clinical symptoms that usually include thickened and dystrophic nails, palmoplantar keratoderma (PPK), glandular cysts and oral leukokeratosis. The study of PC pathophysiology is made challenging because of its low incidence and high complexity. There is no cure or effective treatment for PC. What does this study add? This text reviews recent progress made when studying the pathophysiology of PPK associated with PC. This recent progress points to new possibilities for devising effective therapeutics that may complement current palliative strategies.

Symptomatic mucosal involvement in pachyonychia congenita: challenges in infants and young children

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant genodermatosis caused by a mutation in any one of five keratin genes (KRT6A, KRT6B, KRT6C, KRT16 or KRT17). Characteristic features of PC are painful palmoplantar keratoderma, variable nail dystrophy, cysts, follicular hyperkeratosis and often oral leukokeratosis. Although oral leukokeratosis can go unnoticed, mucosal involvement of the oral cavity and upper airways can manifest with pain during feeding, hoarseness, stridor and, occasionally, life-threatening obstruction.

OBJECTIVES

To characterize patients with PC with symptomatic mucosal involvement.

METHODS

We present a case series of nine children with PC with symptomatic mucosal involvement, all with heterozygous mutations in KRT6A. Seven patients complained of painful feeding problems. Four patients were diagnosed with failure to thrive, three of whom required a feeding tube. Simple feeding solutions were beneficial in most cases. Seven patients had laryngeal involvement and one patient died at 4 years of age from acute laryngeal obstruction.

CONCLUSIONS

It is important for dermatologists and otolaryngologists to be aware that symptomatic mucosal involvement, and very rarely laryngeal obstruction, can occur in patients with PC. Usually simple feeding solutions may prevent complications and failure to thrive. What's already known about this topic? Pachyonychia congenita (PC) is a rare autosomal dominant genodermatosis due to a mutation in any one of five keratin genes. Symptomatic mucosal involvement is an important clinical feature of PC and appears to be more pronounced in KRT6A mutation carriers. Only leukokeratosis is frequently seen in PC and can be one of the earliest signs of disease. Laryngeal involvement is a less common feature. It might be symptomatic but usually presents as hoarseness, stridor and, occasionally, as a life-threatening respiratory distress. What does this study add? In most cases of laryngeal involvement, there is no need for any intervention. Although pain and feeding difficulties are usually attributed to the oral leukokeratosis, they can be related to a phenomenon called 'first bite syndrome' (FBS). Symptomatic mucosal involvement with feeding difficulty is important but can be managed in most cases with simple feeding solutions (e.g. softer nipple with a larger hole, thicker formula and feeding with a syringe). Linked Comment: Youssefian and Vahidnezhad. Br J Dermatol 2020; 182:536-537.

The expression of equine keratins K42 and K124 is restricted to the hoof epidermal lamellae of Equus caballus

The equine hoof inner epithelium is folded into primary and secondary epidermal lamellae which increase the dermo-epidermal junction surface area of the hoof and can be affected by laminitis, a common disease of equids. Two keratin proteins (K), K42 and K124, are the most abundant keratins in the hoof lamellar tissue of Equus caballus. We hypothesize that these keratins are lamellar tissue-specific and could serve as differentiation- and disease-specific markers. Our objective was to characterize the expression of K42 and K124 in equine stratified epithelia and to generate monoclonal antibodies against K42 and K124. By RT-PCR analysis, keratin gene (KRT) KRT42 and KRT124 expression was present in lamellar tissue, but not cornea, haired skin, or hoof coronet. In situ hybridization studies showed that KRT124 localized to the suprabasal and, to a lesser extent, basal cells of the lamellae, was absent from haired skin and hoof coronet, and abruptly transitions from KRT124-negative coronet to KRT124-positive proximal lamellae. A monoclonal antibody generated against full-length recombinant equine K42 detected a lamellar keratin of the appropriate size, but also cross-reacted with other epidermal keratins. Three monoclonal antibodies generated against N- and C-terminal K124 peptides detected a band of the appropriate size in lamellar tissue and did not cross-react with proteins from haired skin, corneal limbus, hoof coronet, tongue, glabrous skin, oral mucosa, or chestnut on immunoblots. K124 localized to lamellar cells by indirect immunofluorescence. This is the first study to demonstrate the localization and expression of a hoof lamellar-specific keratin, K124, and to validate anti-K124 monoclonal antibodies.

Keratin 17 in disease pathogenesis: from cancer to dermatoses

Keratin 17 (K17) is a type I intermediate filament mainly expressed in the basal cells of epithelia. As a multifaceted cytoskeletal protein, K17 regulates a myriad of biological processes, including cell proliferation and growth, skin inflammation and hair follicle cycling. Aberrant overexpression of K17 is found in various diseases ranging from psoriasis to malignancies such as breast, cervical, oral squamous and gastric carcinomas. Moreover, genetic mutation in KRT17 is related to tissue-specific diseases, represented by steatocystoma multiplex and pachyonychia congenita. In this review, we summarize our findings concerning the regulatory mechanisms of K17 overexpression in psoriasis and compare them to the literature relating to other diseases. We discuss data that proinflammatory cytokines, including interleukin-17 (IL-17), IL-22, interferon-gamma (IFN-γ), transforming growth factor-beta (TGF-β) and transcription factors glioma-associated oncogene homolog 1/2 (Gli1/2), Nrf2 and p53 can regulate K17 by transcriptional and translational control. Moreover, post-translational modification, including phosphorylation and ubiquitination, is involved in the regulation of K17 stability and biological functions. We therefore review the current understanding of the K17 regulatory mechanism and its pathogenic role in diseases from dermatoses to cancer. Prospects for anti-K17 therapy in diagnosis, prognosis and disease treatment are also discussed. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Pachyonychia Congenita: A Spectrum of KRT6a Mutations in Australian Patients

BACKGROUND

Pachyonychia congenita (PC) is a rare inherited disorder of keratinization characterised by hypertrophic nail dystrophy, painful palmoplantar blisters, cysts, follicular hyperkeratosis and oral leukokeratosis. It is associated with mutations in five differentiation-specific keratin genes, KRT6A, KRT6B, KRT6C, KRT16, or KRT17.

OBJECTIVES

Living with Pachyonychia Congenita can be isolating. The aim of this paper is to document a single patient's experience within a national context.

METHOD

We report the case of a 2 year old female with an atypical presentation of PC due to a mutation in KRT6A with severely hypertrophic follicular keratoses, skin fragility, relative sparing of nail hypertrophy on one hand and failure to thrive in early infancy. In collaboration with the International Pachyonychia Congenita Research Registry (IPCRR), a database search was performed using Australian residency and KRT6A mutation as inclusion criteria. The IPCRR database was also searched for a matching KRT6A mutation. Six Australian patients were identified in addition to one patient with an identical mutation residing in the United States. The detailed standardized patient questionnaire data was manually collated and analysed.

RESULTS

Fingernail hypertrophy and oral leukokeratosis were the most common features. There was no recording of asymmetric distribution in any other Australian patient. Trouble nursing as an infant and follicular hyperkeratosis also occurred in the American patient, however they did not have asymmetric distribution and the oral leukokeratosis appeared later in life.

CONCLUSION

This case has unique features. Sharing information can assist patients navigating life with this condition.

Loss of FOXA1 Drives Sexually Dimorphic Changes in Urothelial Differentiation and Is an Independent Predictor of Poor Prognosis in Bladder Cancer

We previously found loss of forkhead box A1 (FOXA1) expression to be associated with aggressive urothelial carcinoma of the bladder, as well as increased tumor proliferation and invasion. These initial findings were substantiated by The Cancer Genome Atlas, which identified FOXA1 mutations in a subset of bladder cancers. However, the prognostic significance of FOXA1 inactivation and the effect of FOXA1 loss on urothelial differentiation remain unknown. Application of a univariate analysis (log-rank) and a multivariate Cox proportional hazards regression model revealed that loss of FOXA1 expression is an independent predictor of decreased overall survival. An ubiquitin Cre-driven system ablating Foxa1 expression in urothelium of adult mice resulted in sex-specific histologic alterations, with male mice developing urothelial hyperplasia and female mice developing keratinizing squamous metaplasia. Microarray analysis confirmed these findings and revealed a significant increase in cytokeratin 14 expression in the urothelium of the female Foxa1 knockout mouse and an increase in the expression of a number of genes normally associated with keratinocyte differentiation. IHC confirmed increased cytokeratin 14 expression in female bladders and additionally revealed enrichment of cytokeratin 14-positive basal cells in the hyperplastic urothelial mucosa in male Foxa1 knockout mice. Analysis of human tumor specimens confirmed a significant relationship between loss of FOXA1 and increased cytokeratin 14 expression.

First case of pachyonychia congenita in the Czech Republic

Pachyonychia congenita (PC) is a rare autosomal dominant skin disorder characterized predominantly by hypertrophic nail dystrophy, oral leukokeratosis, and painful palmoplantar keratoderma. It is associated with a mutation in one of five keratin genes, KRT6A, KRT6B, KRT6C, KRT16, or KRT17. The International PC Research Registry (IPCRR) confirms that as of January 2014 there have been 547 cases of PC genetically confirmed. It is estimated that there are between 2000 and 10,000 cases of PC in the world. However, the exact prevalence of PC is not yet established. We report a case of PC-K6a, p.Arg164Pro, in a 40-year-old man. Initially he was diagnosed with onychomycosis and was treated with systemic antifungals. This is the first genetically confirmed case of PC in the Czech Republic.

Mutation p.Leu128Pro in the 1A domain of K16 causes pachyonychia congenita with focal palmoplantar keratoderma in a Chinese family

Pachyonychia congenita (PC), a rare autosomal dominant disorder characterized by hypertrophic nail dystrophy, is classified into two main clinical subtypes: PC-1 and PC-2. PC-1 is associated with mutations in the KRT6A or KRT16 genes, whereas PC-2 is linked to KRT6B or KRT17 mutations. Blood samples were collected from three generations of a new Chinese PC-1 family, including three PC patients and five unaffected family members. A novel missense mutation p.Leu128Pro (c.383T>C) was identified in a highly conserved helix motif in domain 1A of K16. The disease haplotype carried the mutation and cosegregated with the affection status. PolyPhen2 and SIFTS analysis rated the substitution as probably damaging; Swiss-Model analysis indicated that the structure of the mutant protein contained an unnormal α-helix. Overexpression of mutant protein in cultured cells led to abnormal cell morphology.

CONCLUSION

The wider spectrum of KRT16 mutations suggests that changes in codons 125, 127, and 132 are most commonly responsible for PC-1 and that proline substitution mutations at codons 127 or 128 may produce more severe disease. This study extends the KRT16 mutation spectrum and adds new information on the clinical and genetic diversity of PC.

Keratin 16-null mice develop palmoplantar keratoderma, a hallmark feature of pachyonychia congenita and related disorders

Keratin 16 (KRT16 in human, Krt16 in mouse), a type I intermediate filament protein, is constitutively expressed in epithelial appendages and is induced in the epidermis upon wounding and other stressors. Mutations altering the coding sequence of KRT16 cause Pachyonychia Congenita (PC), a rare autosomal dominant disorder characterized by hypertrophic nail dystrophy, oral leukokeratosis, and palmoplantar keratoderma (PPK). PPK associated with PC are extremely painful and compromise patient mobility, making them the most debilitating PC symptom. In this study, we show that, although inherited in a recessive fashion, the inactivation of Krt16 in mice consistently causes oral lesions as well as PPK-like hyperkeratotic calluses on Krt16^−/− front and hind paws, which severely compromise the animals’ ability to walk. Our findings call into question the view that PC-related PPK arise exclusively as a gain-of-function on the account of dominantly acting mutated keratins, and highlight the key role of modifiers in the clinical heterogeneity of PC symptoms.

Steatocystoma multiplex

A 40-year-old man presented with multiple papules on his head and neck. The lesions had been present for about 15 years. The patient was treated for acne for 6 months, but no improvement was noted. A biopsy was performed and microscopic findings were consistent with steatocystoma multiplex.

The autoimmune regulator (AIRE), which is defective in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy patients, is expressed in human epidermal and follicular keratinocytes and associates with the intermediate filament protein cytokeratin 17

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) syndrome, which is caused by mutation of the autoimmune regulator (AIRE) gene, is a highly variable disease characterized by multiple endocrine failure, chronic mucocutaneous candidiasis, and various ectodermal defects. AIRE is a transcriptional regulator classically expressed in medullary thymic epithelial cells, monocytes, macrophages, and dendritic cells. Previous studies have suggested that AIRE can shuttle between the nucleus and cytoplasm of cells, although its cytoplasmic functions are poorly characterized. Through mass spectrometry analysis of proteins co-immunoprecipitating with cytoplasmic AIRE, we identified a novel association of AIRE with the intermediate filament protein cytokeratin 17 (K17) in the THP-1 monocyte cell line. We confirmed AIRE expression in HaCaT epidermal keratinocytes, as well as its interaction with K17. Confocal microscopy of human fetal and adult scalp hair follicles demonstrated a cytoplasmic pattern of AIRE staining that moderately colocalized with K17. The cytoplasmic association of AIRE with the intermediate filament network in human epidermal and follicular keratinocytes may provide a new path to understanding the ectodermal abnormalities associated with the APECED syndrome.

Keratin gene mutations in disorders of human skin and its appendages

Keratins, the major structural protein of all epithelia are a diverse group of cytoskeletal scaffolding proteins that form intermediate filament networks, providing structural support to keratinocytes that maintain the integrity of the skin. Expression of keratin genes is usually regulated by differentiation of the epidermal cells within the stratifying squamous epithelium. Amongst the 54 known functional keratin genes in humans, about 22 different genes including, the cornea, hair and hair follicle-specific keratins have been implicated in a wide range of hereditary diseases. The exact phenotype of each disease usually reflects the spatial expression level and the types of mutated keratin genes, the location of the mutations and their consequences at sub-cellular levels as well as other epigenetic and/or environmental factors. The identification of specific pathogenic mutations in keratin disorders formed the basis of our understanding that led to re-classification, improved diagnosis with prognostic implications, prenatal testing and genetic counseling in severe keratin genodermatoses. Molecular defects in cutaneous keratin genes encoding for keratin intermediate filaments (KIFs) causes keratinocytes and tissue-specific fragility, accounting for a large number of genetic disorders in human skin and its appendages. These diseases are characterized by keratinocytes fragility (cytolysis), intra-epidermal blistering, hyperkeratosis, and keratin filament aggregation in severely affected tissues. Examples include epidermolysis bullosa simplex (EBS; K5, K14), keratinopathic ichthyosis (KPI; K1, K2, K10) i.e. epidermolytic ichthyosis (EI; K1, K10) and ichthyosis bullosa of Siemens (IBS; K2), pachyonychia congenita (PC; K6a, K6b, K16, K17), epidermolytic palmo-plantar keratoderma (EPPK; K9, (K1)), monilethrix (K81, K83, K86), ectodermal dysplasia (ED; K85) and steatocystoma multiplex. These keratins also have been identified to have roles in apoptosis, cell proliferation, wound healing, tissue polarity and remodeling. This review summarizes and discusses the clinical, ultrastructural, molecular genetics and biochemical characteristics of a broad spectrum of keratin-related genodermatoses, with special clinical emphasis on EBS, EI and PC. We also highlight current and emerging model tools for prognostic future therapies. Hopefully, disease modeling and in-depth understanding of the molecular pathogenesis of the diseases may lead to the development of novel therapies for several hereditary cutaneous diseases.

Novel keratins identified by quantitative proteomic analysis as the major cytoskeletal proteins of equine (Equus caballus) hoof lamellar tissue

The dermo-epidermal interface that connects the equine distal phalanx to the cornified hoof wall withstands great biomechanical demands, but is also a region where structural failure often ensues as a result of laminitis. The cytoskeleton in this region maintains cell structure and facilitates intercellular adhesion, making it likely to be involved in laminitis pathogenesis, although it is poorly characterized in the equine hoof lamellae. The objective of the present study was to identify and quantify the cytoskeletal proteins present in the epidermal and dermal lamellae of the equine hoof by proteomic techniques. Protein was extracted from the mid-dorsal epidermal and dermal lamellae from the front feet of 5 Standardbred geldings and 1 Thoroughbred stallion. Mass spectrometry-based spectral counting techniques, PAGE, and immunoblotting were used to identify and quantify cytoskeletal proteins, and indirect immunofluorescence was used for cellular localization of K14 and K124 (where K refers to keratin). Proteins identified by spectral counting analysis included 3 actin microfilament proteins; 30 keratin proteins along with vimentin, desmin, peripherin, internexin, and 2 lamin intermediate filament proteins; and 6 tubulin microtubule proteins. Two novel keratins, K42 and K124, were identified as the most abundant cytoskeletal proteins (22.0 ± 3.2% and 23.3 ± 4.2% of cytoskeletal proteins, respectively) in equine hoof lamellae. Immunoreactivity to K14 was localized to the basal cell layer, and that to K124 was localized to basal and suprabasal cells in the secondary epidermal lamellae. Abundant proteins K124, K42, K14, K5, and α(1)-actin were identified on 1- and 2-dimensional polyacrylamide gels and aligned with the results of previous studies. Results of the present study provide the first comprehensive analysis of cytoskeletal proteins present in the equine lamellae by using mass spectrometry-based techniques for protein quantification and identification.

Autosomal-dominant woolly hair resulting from disruption of keratin 74 (KRT74), a potential determinant of human hair texture

Autosomal-dominant woolly hair (ADWH) is a rare disorder characterized by tightly curled hair. The molecular basis of ADWH has not previously been reported. In this study, we identified a Pakistani family with ADWH. The family showed linkage to chromosome 12q12-q14.1, containing the type II keratin gene cluster. We discovered a heterozygous mutation, p.Asn148Lys, within the helix initiation motif of the keratin 74 (KRT74) gene in all affected family members. KRT74 encodes the inner root sheath (IRS)-specific epithelial (soft) keratin 74. We demonstrate that the mutant K74 protein results in disruption of keratin intermediate filament formation in cultured cells, most likely in a dominant-negative manner. Furthermore, we sequenced the mouse Krt71-74 genes in the dominant Caracul-like 4 (Cal4) allele, which is characterized by a wavy-coat phenotype and maps to the same region of mouse chromosome 15 as the Caracul (Ca) and Reduced coat (Rco) alleles. We identified a heterozygous mutation, p.Glu440Lys, not in Krt74 but in the neighboring gene, Krt71. Krt71 was previously reported to harbor Ca and Rco mutations, as well as a coding SNP that is associated with curly-coated dogs. In this study, we define the ADWH phenotype resulting from a mutation in a hair-follicle-specific epithelial keratin in humans. Our findings not only further underscore the crucial roles of the IRS-specific epithelial keratin genes Krt71-74 in hair disorders but also open the possibility that these genes might function as genetic determinants of normal variation in hair texture across mammalian species.

Disadhesion of epidermal keratinocytes: a histologic clue to palmoplantar keratodermas caused by DSG1 mutations

BACKGROUND

Recent developments in molecular genetics may lead to re-examination of the histopathology of inherited palmoplantar keratodermas (PPKs) based on more precise groupings of the various entities and syndromes.

OBJECTIVE

We sought to characterize the histopathological findings in PPKs associated with mutations in DSG1, which encodes desmoglein 1.

METHODS

We studied the histopathology of 3 cases of keratosis palmoplantaris striata type I and one case of diffuse PPK, all associated with autosomal-dominant mutations in DSG1. Our cases for comparison included 4 cases with Mal de Meleda PPK associated with autosomal-recessive SLURP1 mutations, one case with pachyonychia congenita type II PPK associated with an autosomal-dominant KRT17 mutation, and one case with focal PPK associated with an autosomal-dominant KRT16 mutation.

RESULTS

The distinguishing histopathological features of the 3 keratosis palmoplantaris striata type I cases and the diffuse PPK case associated with DSG1 mutation were: varying degrees of widening of the intercellular spaces and partial disadhesion of keratinocytes in the mid and upper epidermal spinous cell layers, often extending to the granular cell layer. These findings, which are associated with haploinsufficiency of desmoglein 1, were not observed in any of the other 6 PPK cases. Mild perinuclear eosinophilic condensations and cytoplasmic vacuolizations were observed in the spinous cell layer keratinocytes of the pachyonychia congenita type II PPK and the nonspecified focal PPK cases.

LIMITATIONS

There were a limited number of patients and control patients with hereditary PPKs.

CONCLUSION

Widening of the intercellular spaces and disadhesion of epidermal keratinocytes may serve as a histologic clue to PPKs caused by DSG1 mutations.

Pachyonychia congenita type 2, N92S mutation of keratin 17 gene: clinical features, mutation analysis and pathological view

Pachyonychia congenita (PC) type 2 is a rare inherited genetic disease characterized by hypertrophic nail dystrophy, palmoplantar hyperkeratosis and multiple pilosebaceous cysts. In some cases, natal teeth and hair abnormalities may be present. It is caused by mutations in keratin 17 or its expression partner keratin 6b. Here, an N92S (p.Asn92Ser) germline keratin 17 gene mutation in a pachyonychia congenita type 2 female patient is presented. The pedigree includes the 15 members of a family who showed a severe expression of the phenotype for six generations with a similar clinical picture consisting of sebaceous cysts, nail dystrophy, hyperkeratosis, hair abnormalities, natal teeth, hoarseness and hyperhydrosis. In conclusion, we emphasize the importance of diagnosing and managing pachyonychia congenita in childhood for the assistance of affected children and for the development of potential therapies.

Pachyonychia congenita type I presenting with subtle nail changes

Pachyonychia congenita type I is an autosomal dominant disorder where nail abnormalities are a constant feature and develop during childhood. We report here a family with pachyonychia congenita type I and very mild nail changes to underline that this diagnosis should be considered even in the absence of severe nail thickening.