Novel and recurrent mutations in the genes encoding keratins K6a, K16 and K17 in 13 cases of pachyonychia congenita

Autosomal recessive plantar keratoderma with ragged periungual hyperkeratosis caused by a homozygous missense variant in KRT16

In the present study, we report a consanguineous Kuwaiti pedigree with pseudo-dominant inheritance of a recessive KRT16 variant in which homozygotes had focal nonepidermolytic palmoplantar keratoderma accompanied by ragged periungual hyperkeratosis. The key value of this submission is that we believe we have identified the first autosomal recessive inherited skin disorder resulting from pathogenic variants in the keratin 16 gene, KRT16. Our findings expand both the genetic basis and phenotypic expression of inherited KRT16-related disorders.

Partial Loss of Function ABCA12 Mutations Generate Reduced Deposition of Glucosyl-Ceramide, Leading to Patchy Ichthyosis and Erythrodermia Resembling Erythrokeratodermia Variabilis et Progressiva (EKVP)

Ichthyoses are genetically determined cornification disorders of the epidermis characterized by the presence of different degrees of scaling, hyperkeratosis, and erythroderma often associated with palmoplantar keratoderma. Different classifications of these diseases have been proposed, often based upon the involved genes and/or the clinical presentation. The clinical features of these diseases present some overlap of phenotypes among distinct genetic entities, depending mainly on the penetrance of mutations. In this study, using a clinical, genetic, and molecular approach, we analyzed a family with two affected members who had clinical and histological features resembling erythrokeratodermia variabilis (EKV) or a type of erythrodermic hyperkeratosis with palmoplantar keratoderma. Despite of the clinical presentation, we demonstrated that the affected patients were genetically double heterozygous for two different mutations in the ABCA12 gene, known to be responsible for harlequin ichthyosis. To explain the mild phenotype of our patients, we performed a molecular characterization of the skin. In the upper layers of the epidermis, the results showed a patchy presence of the glucosyl-ceramides (GlcCer), which is the lipid transported by ABCA12, fundamental in contributing to skin impermeability. Indeed, the two mutations detected do not completely abolish ABCA12 activity, indicating that the mild phenotype is due to a partial loss of function of the enzyme, thus giving rise to an intermediate phenotype resembling EKVP, due to a partial depletion of GlcCer deposition.

KERATIN 17-related recessive atypical pachyonychia congenita with variable hair and tooth anomalies

We present the first pachyonychia congenita (PC) to involve all ectodermal derivatives and the first recessive KRT17-related PC in total seven members of two consanguineous Pakistani families. This atypical PC is characterized by an unusual combination of pachyonychia, plantar keratoderma, folliculitis, alopecia, sparse eyebrows, dental anomalies and variable acanthosis nigricans of neck, dry skin, palmoplantar hyperhidrosis, recurrent blisters on soles and/or arms, rough sparse hair on scalp and keratosis pilaris. By exome sequencing we detected homozygous KRT17 c.281G>A (p.(Arg94His)) in affected individuals, and linkage mapping indicated a single locus. Heterozygous variants in KRT17 cause PC2 (PC-K17) with main characteristics of pachyonychia, subungual keratosis, palmoplantar keratoderma, hyperhidrosis, oral leukokeratosis and epidermal cysts, or steatocystoma multiplex, both with dominant inheritance. The causative variant has been reported in heterozygous state in a family afflicted with severe steatocystoma multiplex and in a sporadic PC2 case, and thus we also define a third phenotype related to the variant. Both exome sequencing and linkage mapping demonstrated recessive inheritance whereas Sanger sequencing indicated heterozygosity for the causal variant, reiterating caution for simple targeted sequencing for genetic testing. Testing parents for variants found in sibs could uncover recessive inheritance also in other KRT genes.

Post Zygotic, Somatic, Deletion in KERATIN 1 V1 Domain Generates Structural Alteration of the K1/K10 Dimer, Producing a Monolateral Palmar Epidermolytic Nevus

Palmoplantar keratodermas (PPKs) are characterized by thickness of stratum corneum and epidermal hyperkeratosis localized in palms and soles. PPKs can be epidermolytic (EPPK) or non epidermolytic (NEPPK). Specific mutations of keratin 16 (K16) and keratin 1 (K1) have been associated to EPPK, and NEPPK. Cases of mosaicism in PPKs due to somatic keratin mutations have also been described in scientific literature. We evaluated a patient presenting hyperkeratosis localized monolaterally in the right palmar area, characterized by linear yellowish hyperkeratotic lesions following the Blaschko lines. No other relatives of the patient showed any dermatological disease. Light and confocal histological analysis confirmed the presence of epidermolityic hyperkeratosis. Genetic analysis performed demonstrates the heterozygous deletion NM_006121.4:r.274_472del for a total of 198 nucleotides, in KRT1 cDNA obtained by a palmar lesional skin biopsy, corresponding to the protein mutation NP_006112.3:p.Gly71_Gly137del. DNA extracted from peripheral blood lymphocytes did not display the presence of the mutation. These results suggest a somatic mutation causing an alteration in K1 N-terminal variable domain (V1). The deleted sequence involves the ISIS subdomain, containing a lysine residue already described as fundamental for epidermal transglutaminases in the crosslinking of IF cytoskeleton. Moreover, a computational analysis of the wild-type and V1-mutated K1/K10 keratin dimers, suggests an unusual interaction between these keratin filaments. The mutation taster in silico analysis also returned a high probability for a deleterious mutation. These data demonstrate once again the importance of the head domain (V1) of K1 in the formation of a functional keratinocyte cytoskeleton. Moreover, this is a further demonstration of the presence of somatic mutations arising in later stages of the embryogenesis, generating a mosaic phenotype.

Distinctions in the Management, Patient Impact, and Clinical Profiles of Pachyonychia Congenita Subtypes

Introduction

Pachyonychia congenita (PC) is a rare dermatosis that confers lifelong physical and emotional morbidities in affected patients. However, the clinical findings, treatments, and psychosocial impact of this disease have not been adequately described. The International PC Research Registry (IPCRR), a multinational initiative to collect data on PC patients, has allowed an opportunity to distinguish the salient features of this disease. We aimed to characterize the breadth and extent of nail disease, treatments, and quality of life in PC patients, and to describe any significant differences in clinical presentation or treatment of PC subtypes.

Methods

The most recent IPCRR patient survey data consisting of an 857-response questionnaire and a 102-response addendum were analyzed in a retrospective analysis. The survey data were collected as part of a multinational, multicenter initiative and comprise the largest representative population of PC to date. Participants (survey respondents) were included in the study based on questionnaire responses and a genetic confirmation of having a PC subtype.

Results

A total of 857 survey responses were collected. Genetic variations among PC subtypes influence nail disease onset and severity of symptoms. Nail disease negatively impacts patients' emotional health, especially during the adolescent and young adult years. Nail treatment tools vary little in terms of effectiveness and acquired infection rates.

Conclusion and Discussion

Patients with different PC subtypes have distinct clinical nail presentations and psychosocial impact. Genetic testing should be used to confirm PC diagnoses. Further characterization of PC, especially the rarer subtypes, may allow for more individualized patient education.

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.

Role of the keratin 1 and keratin 10 tails in the pathogenesis of ichthyosis hystrix of Curth Macklin

Ichthyosis Hystrix of Curth-Macklin (IH-CM) is a rare manifestation of epidermolytic ichthyosis (EI) that is characterised by generalised spiky or verrucous hyperkeratosis. The disorder is further distinguished by the presence of binucleated cells in the affected skin, whereas epidermolysis and clumping of tonofilaments, as seen in EI, are absent. While IH-CM is associated with mutations in the keratin 1 (KRT1) gene, reports to date have indicated that mutations in the KRT1 gene result in an aberrant and truncated protein tail, essentially affecting the function of the V2 domain. Here, we studied a female sporadic patient who was born with diffused erythrodermic hyperkeratosis and who presented at the age of 13 months with an intense and widespread hyperkeratosis with a papillomatous appearance and typical palmoplantar keratoderma. Genetic analysis demonstrated a “de novo” mutation in the keratin 10 gene (KRT10) consisting of a three-base-pair deletion, resulting in the substitution of amino acids p.Glu445 and p.Ile446 by Asp at the end of the 2B domain of the protein. We performed structural and functional studies showing that this mutation modifies the structure of the paired 2B and V2 K1/10 domains, leading to the disease phenotype. Our results highlight the importance and complexity of the KRT1/10 V2 domain in keratin dimer formation and the potential consequences of its alteration.

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.

Steatocystoma multiplex is associated with the R94C mutation in the KRTl7 gene

Steatocystoma multiplex (SM) is an uncommon disorder, characterized by numerous skin-colored subcutaneous cysts. A number of SM pedigrees have been identified with mutations in the keratin 17 (KRT17) gene. The present study examined a four-generation Chinese pedigree with an autosomal dominant mode of inheritance and examined its genetic basis. A review of the literature on KRT17 gene mutations in the SM pedigree was also performed to investigate the KRT17 gene mutation and genotype-phenotype correlation. Exon 1 of the KRTl7 gene was amplified using polymerase chain reaction (PCR) from genomic DNA obtained, which was obtained from 25 family members in the selected Chinese pedigree and from 100 unrelated control individuals. The DNA was then subjected to automatic DNA sequencing. Genealogical investigations demonstrated an autosomal dominant pattern, and direct sequencing of the PCR product revealed a heterozygous mutation, c.280C/T (R94C), which was located in exon 1 of the KRT17 gene in all 10 affected family members. The mutation was not identified in the 15 unaffected family members or in the 100 unrelated control individuals. Therefore, the present study identified a causative mutation in the KRT17 gene in a large Chinese SM pedigree, exhibiting autosomal dominance. A review of the literature suggested that, in addition to the mutation factor, other modifying factors contribute to the phenotype of familial SM.

New described dermatological disorders

Many advances in dermatology have been made in recent years. In the present review article, newly described disorders from the last six years are presented in detail. We divided these reports into different sections, including syndromes, autoinflammatory diseases, tumors, and unclassified disease. Syndromes included are “circumferential skin creases Kunze type” and “unusual type of pachyonychia congenita or a new syndrome”; autoinflammatory diseases include “chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE) syndrome,” “pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH) syndrome,” and “pyogenic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PAPASH) syndrome”; tumors include “acquired reactive digital fibroma,” “onychocytic matricoma and onychocytic carcinoma,” “infundibulocystic nail bed squamous cell carcinoma,” and “acral histiocytic nodules”; unclassified disorders include “saurian papulosis,” “symmetrical acrokeratoderma,” “confetti-like macular atrophy,” and “skin spicules,” “erythema papulosa semicircularis recidivans.”

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.

Molecular diagnosis of genodermatoses

The progress of molecular genetics helps clinicians to prove or exclude a suspected diagnosis for a vast and yet increasing number of genodermatoses. This leads to precise genetic counselling, prenatal diagnosis and preimplantation genetic haplotyping for many inherited skin conditions. It is also helpful in such occasions as phenocopy, late onset and incomplete penetrance, uniparental disomy, mitochondrial inheritance and pigmentary mosaicism. Molecular methods of two genodermatoses are explained in detail, i.e. genodermatoses with skin fragility and neurofibromatosis type 1.

Diagnostic utility of cytokeratin 17 immunostaining in morpheaform basal cell carcinoma and for facilitating the detection of tumor cells at the surgical margins

BACKGROUND

The morpheaform subtype of basal cell carcinoma (BCC) often presents a diagnostic histological challenge, and its true margin may be difficult to determine with accuracy. This tumor may also be difficult to distinguish from other adnexal neoplasms having a benign clinical course. Previous work has shown that cytokeratin 17 (CK17 or K17) expression is high in BCC.

OBJECTIVE

To confirm the expression of K17 across the subtypes of superficial, nodular and morpheaform BCC variants and to compare K17 expression in each of these subtypes of BCC with that in two other adnexal neoplasms.

METHODS

Tissue specimens from each tumor category were randomly collected, immunolabeled, and scored for K17 expression according to intensity and extent of immunostaining.

RESULTS

Our results indicate that K17 is a useful marker in the identification and outlining of BCC. Moreover, in morpheaform BCC, K17 immunostaining clearly detected individual tumor cells well away from the dermal tumor strands that otherwise seemed nonmalignant according to hematoxylin and eosin staining alone. In addition, the expression of K17 in morpheaform BCC is capable (100% of specimens; p < .001) of distinguishing this tumor from desmoplastic trichoepithelioma.

CONCLUSION

We propose that K17 immunostaining could improve the diagnostic and surgical management of these tumors.

Hereditary leukonychia, or porcelain nails, resulting from mutations in PLCD1

Hereditary leukonychia (porcelain nails or white nails) is a rare nail disorder with an unknown genetic basis. To identify variants in a gene underlying this phenotype, we identified four families of Pakistani origin showing features of hereditary leukonychia. All 20 nails of each affected individual were chalky and white in appearance, consistent with total leukonychia, with no other cutaneous, appendageal, or systemic findings. By using Affymetrix 10K chip, we established linkage to chromosome 3p21.3-p22 with a LOD score (Z) of 5.1. We identified pathogenic mutations in PLCD1 in all four families, which encodes phosphoinositide-specific phospholipase C delta 1 subunit, a key enzyme in phosphoinositide metabolism. We then identified localization of PLCD1 in the nail matrix. It was recently shown that PLCD1 is a component of the human nail plate by proteomic analysis and is localized in the matrix of human nails. Furthermore, mutations detected in PLCD1 resulted in reduced enzymatic activity in vitro. Our data show that mutations in PLCD1 underlie hereditary leukonychia, revealing a gene involved in molecular control of nail growth.

Nail disorders in children: diagnosis and management

Nail disorders in children can be divided into seven categories. The first is physiologic alterations, which every physician should be aware of in order to reassure parents. These usually disappear with age and do not require any treatment. Among congenital and inherited conditions, the nail-patella syndrome, with its pathognomonic triangular lunula, should not be missed as recognition of the disease allows early diagnosis of associated pathologies. The most common infection is the periungual wart, whose treatment is delicate. Herpetic whitlow should be distinguished from bacterial whitlow as their therapeutic approaches differ. Dermatologic diseases encompass eczema, psoriasis, lichen planus, lichen striatus, trachyonychia, and parakeratosis pustulosa. Lichen planus, when it presents as in adults, is important to recognize because, if not treated, it may lead to permanent nail loss. Systemic or iatrogenic nail alterations may be severe but are usually not the first clue to the diagnosis. Beau lines on several fingernails are very common in children after temperature crest. Tumors are rare in children. Radiographic examination allows confirmation of the diagnosis of subungual exostosis. Other cases should undergo biopsy. Single-digit longitudinal melanonychia in children is mostly due to nevi. Its management should be tailored on a case-by-case basis. Acute trauma should never be underestimated in children and hand surgeons should be involved if necessary. Onychophagia and onychotillomania are responsible for chronic trauma.

p63 – Key molecule in the early phase of epithelial abnormality in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common lung disease predisposing lung cancer. To clarify the early phase of epithelial abnormalities in IPF, we used an in vitro squamous metaplasia model, transforming growth factor beta1 (TGF beta1)-treated airway epithelial cells (BEAS-2B). The model repeated the expression of squamous epithelial character, such as involucrin, and keratin 6 and 14. DNA microarray analysis disclosed a unique expression signature in TGF beta1-treated airway epithelial cells, 20 specifically up-regulated genes including p63, jagged 1 (jag1) and the genes of structure proteins. Western blotting and RT-PCR analysis revealed that DeltaNp63alpha was the dominant isoform of p63 in our experimental model. Immunohistochemical analysis demonstrated the expression of p63 and jag1 in lung tissues of IPF. Inhibition of p63 with siRNA caused the down-regulation of jag1 expression, but not of involucrin, or keratin 6 and 14. Interestingly, the up-regulation of p63 was totally suppressed by N-acetyl-l-cysteine (NAC), but not by dexamethasone or pirfenidone. Thus, the p63-jag1 pathway may be up-regulated at an early phase of epithelial abnormalities in IPF, which can be overcome by NAC even in the TGF beta1-rich milieu.

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

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant keratin disorder, subdivided into two major variants, PC-1 and PC-2. Predominant characteristics include hypertrophic nail dystrophy, focal palmoplantar keratoderma and oral leukokeratosis. Multiple steatocystomas that develop during puberty are a useful feature distinguishing PC-2 from PC-1. At the molecular level it has been shown that mutations in keratin K6a or K16 cause PC-1 whereas those in K6b or K17 lead to PC-2.

OBJECTIVE

To identify mutations in 22 families presenting with clinical symptoms of either PC-1/focal non-epidermolytic palmoplantar keratoderma (FNEPPK) or PC-2.

METHODS

Mutation analysis was performed on genomic DNA from PC patients by direct sequencing.

RESULTS

Here, we report four new missense and five known mutations in K6a; one new deletion and three previously identified missense mutations in K16; plus one known mutation in K17.

CONCLUSION

With one exception, all these heterozygous mutations are within the highly conserved helix boundary motif regions at either end of the keratin rod domain. In one sporadic case, a unique mutation in K16 resulting in deletion of 24bp was found within the central rod domain, in a child with a phenotype predominantly consisting of focal plantar keratoderma. The identification of mutations in cases of PC is prerequisite for future development of gene-specific and/or mutation-specific therapies.

A novel missense mutation L468Q of keratin 6a in pachyonychia congenita type 1

BACKGROUND

Pachyonychia congenita is an autosomal dominant disorder that usually develops in early infancy. The major features of the syndrome are hypertrophic nail dystrophy, palmoplantar keratoderma and oral leucokeratosis, accompanied by other ectodermal defects, according to subtype.

OBJECTIVE

To analyse the K6a gene mutation in a sporadic Chinese patient with pachyonychia congenita type 1 (PC-1) and to explore the relationship between the genotype and phenotype of PC-1.

METHODS

Genomic DNA was extracted from peripheral blood of the patient with PC-1 and 100 unrelated controls. The whole coding region of K6a gene was amplified using long-range polymerase chain reaction (PCR); nested PCR was then used to amplify the mutation 'hot-spot' of the K6a gene. The PCR products were directly sequenced to detect the mutation.

RESULTS

A novel missense mutation L468Q in the helix 2B domain of the K6a polypeptide was identified in the patient but not in the healthy individuals from the family and 100 unrelated control individuals.

CONCLUSIONS

We describe this mutation for the first time, and provide further evidence that the helix boundary motif sequences of K6a are a mutation 'hot-spot'.

Keratin expression provides novel insight into the morphogenesis and function of the companion layer in hair follicles

Hair follicles cycle between stages of growth (anagen) and metabolic quiescence (telogen) throughout life. In mature follicles, transition from telogen back into anagen involves the activation, proliferation, and differentiation of epithelial stem cells located in the bulge, a specialization of the outer root sheath. Recent studies identified keratin 6a (K6a) transcripts as enriched in bulge epithelial stem cells in mouse skin. We used messenger RNA probes, antibodies, a LacZ reporter mouse model, and whole-mount staining assays to investigate the regulation of mK6a during mouse postnatal hair cycling, and compare it to mK75, a companion layer (Cl) marker. We find that mK75 regulation parallels that of inner root sheath (IRS) markers, with expression onset at anagen IIIa above the new hair bulb and subsequent spreading towards the bulge. Although also occurring in the Cl, mK6a expression begins at anagen IIIb in differentiating cells located proximal to the bulge, and subsequently spreads towards the hair bulb. mK6a and mK75 thus exhibit temporally distinct, and spatially opposed, expression patterns in the Cl during postnatal anagen. These findings provide novel insight into the morphogenesis and properties of the Cl, and raise the distinct possibility that it is an integral part of the IRS compartment.

Childhood Nail Diseases

The diagnosis of pediatric nail populations is complicated because a large proportion of pediatric nail presentations involve parents bringing in their children with questions regarding nail appearance rather than the plain presentation of a disease or functional problem. Parents are concerned whether the nails are normal, if they are uncomfortable for the baby or child, if the nails will affect walking or other future function, or if the changes are of wider significance and suggest more sinister medical problems than are yet apparent. To address these concerns, the clinician needs a good grasp of what is normal.

The genetic basis of pachyonychia congenita

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

Challenges in developing therapies for rare diseases including pachyonychia congenita

The ability to attract sufficient resources to effectively develop therapeutics for rare diseases is a daunting task. This review summarizes existing resources for rare diseases and discusses some of the challenges and strategies associated with developing therapies for small patient populations with an emphasis on pachyonychia congenita.

Hair and nail relationship

Hair and nails are often stated to have much in common in relation to their origin, anatomical structures, and common involvement in many diseases. Hair and nails are predominantly epithelial structures derived from primitive epidermis and made up of keratinous fibrils embedded in a sulfur-rich matrix. It was first noted early in the 20th century that the nail unit was comparable in several respects to a hair follicle sectioned longitudinally and laid on on its side. The epithelial components of hair follicle and nail apparatus are differentiated epidermal structures that may be involved jointly in several ways as congenital and hereditary anomalies and acquired conditions such as alopecia areata, lichen planus, iatrogenic causes, and fungal infection. Multielemental characterization of human hair and nails shows that even after sample washing, many elements are enriched in the surface of the nails.

Genetics of Corneal Disease for the Ocular Surface Clinician

Advances in the understanding of inherited corneal and external diseases may allow interventions that prevent the substantial vision impairment currently caused by these diseases. The observant clinician may first recognize inherited corneal and external diseases based on clinical examination and a careful family history. Researchers using positional cloning and candidate gene techniques have identified several disease-causing genes. Identification of the genes responsible for inherited corneal and external diseases will lead to more definitive diagnoses and represent the first step in development of effective therapies. Future endeavors are directed toward identifying additional inherited corneal and external diseases, the genes that cause them, and possible gene therapies to improve visual outcomes.

Palmoplantar keratodermas

The palmoplantar skin is a highly specialized tissue which is able to resist mechanical trauma and other physical stress. In recent years the more descriptive classification of keratodermas has switched to an exact molecular genetic view where gene functions are considered. Palmoplantar keratodermas can be separated in the following functional subgroups: disturbed gene fuctions in structural proteins (keratins), cornified envelope (loricrin, transglutaminase), cohesion (plakophilin, desmoplakin, desmoglein1), cell-to-cell communication (connexins), and transmembrane signal transduction (cathepsin C). This review intends to emphasize the typical clinical aspects and symptom complexes associated with palmoplantar keratodermas which enable the astute dermatologist to make a clinical diagnosis. In addition the molecular genetic knowledge on the topic is given which is necessary to confirm the clinical diagnosis.

Avances biomoleculares en los trastornos epidérmicos hereditarios

In recent years, the genes responsible for many hereditary skin diseases have been discovered. These genes encode different proteins that participate in the terminal differentiation of the epidermis, so their alteration or absence causes a keratinization disorder and/or an increase in skin fragility. Thanks to genetic analyses, we have been able to understand the physiopathology of numerous genodermatoses and we have become closer to diagnosing many others. In the not-too-distant future, biomolecular techniques may foreseeably help us prevent and treat these processes, which include skin diseases as serious as epidermolysis bullosa or epidermolytic hyperkeratosis. In this article, we will study the most recent biomolecular findings referring to keratinization and epidermal disorders, mentioning the altered genes and/ or the defective proteins that cause them.

Keratins and skin disorders

The association of keratin mutations with genetic skin fragility disorders is now one of the best-established examples of cytoskeleton disorders. It has served as a paradigm for many other diseases and has been highly informative for the study of intermediate filaments and their associated components, in helping to understand the functions of this large family of structural proteins. The keratin diseases have shown unequivocally that, at least in the case of the epidermal keratins, a major function of intermediate filaments is to provide physical resilience for epithelial cells. This review article reflects on the variety of phenotypes arising from mutations in keratins and the reasons for this variation.

In vivo alteration of the keratin 17 gene in hair follicles by oligonucleotide-directed gene targeting

Using intradermal injection of a chimeric RNA-DNA oligonucleotide (RDO) or a single-stranded oligonucleotide (ssODN) into murine skin, we attempted to make a dominant mutation (R94p) in the conserve alpha-helical domain of keratin 17 (K17), the same mutation found in pachyononychia congenichia type 2 (PC-2) patients with phenotypes ranging from twisted hair and multiple pilosebaceous cysts. Both K17A-RDO and -ssODN contained a single base mismatch (CGC to CCC) to alter the normal K17 sequence to cause an amino acid substitution (R94P). The complexes consisting of oligonucleotides and cationic liposomes were injected to C57B1/6 murine skin at 2 and 5 day after birth. Histological examination of skin biopsies at postnatal day 8 from several mice showed consistent twisted hair shafts or broken hair follicles at the sebaceous gland level and occasional rupture of the hair bulb or epidermal cyst-like changes. In the injected area, the number of full anagen hair follicles decrease by 50%. Injection of the control oligonucleotide, identical to K17A-RDO but containing no mismatch to the normal sequence, did not result in any detectable abnormality. The frequency of gene alteration was lower than 3%, according to the restriction fragment length polymorphism (RFLP) analysis of the genomic DNA isolated by dissection of hair follicles from slides. Although intradermal injection of K17A-RDO or K17-ssODN caused a dominant mutation in K17 affecting hair growth and morphology, these phenotypic changes were transient either due to the compensation of K17 by other keratins or the replacement of the mutated cells by normal surrounding cells during hair growth.

Case study: pachyonychia congenita: a mixed type II-type IV presentation

A 52-year-old woman in good health with a family history negative for dermatologic diseases presented to our department with thickening and dystrophy of all her fingernails and toenails that started when she was born. She also had hyperkeratosis on the palms of her hands and soles of her feet that was confined to sites of pressure and recurrent plantar blisters that began appearing at puberty. The patient reported marked pain while walking from such plantar involvement. Her medical history revealed a persistent hoarseness; palmoplantar hyperhidrosis; and the appearance of numerous cysts on her back, neck, and scalp since she was 20 years old. These latter lesions had been diagnosed as multiple steatocystoma on the basis of the histologic features. Upon examination, all of her fingernails and toenails appeared shortened, thickened,and dystrophic (Figures 1-3). In addition, they presented subungual keratosis and a yellowish-gray color. Hyperkeratosis and small ulcerations were present on the perionychium. Palmoplantar keratoderma was evident, especially on the soles,in association with superficial erosions (Figure 4). Keratosis pilaris was evident on the extensor surfaces of the forearms as well as on the anterior surfaces of the legs. Multiple nodules were detected on the patient's neck, trunk, and axillary regions(Figure 5). They consisted of multiplex steatocystoma and were characterized by a hemispheric shape, a normal-appearing skin color, and by an elastic consistency on palpation. Oral and dental changes were not detected, although hair anomalies were evident. Laboratory parameters disclosed eosinophilia and increased total IgE levels. The results of serum protein electrophoresis was normal, as were those concerning hepatic and renal functions. The ophthalmology examination showed neither corneal dyskeratosis nor cataracts. The neurologic-psychiatric visit revealed slight mental retardation.

A Novel Mutation in the Second Half of the Keratin 17 1A Domain in a Large Pedigree with Delayed-Onset Pachyonychia Congenita Type 2

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

Clouston Syndrome Can Mimic Pachyonychia Congenita

We studied three families suffering from nail abnormalities who had previously been diagnosed as pachyonychia congenita. No keratin gene mutations were detected. Sequencing of connexin 30 (GJB6 gene) in these patients identified heterozygous missense mutations G11R and A88V that are known to be associated with Clouston syndrome. This unexpected finding expands the Clouston syndrome phenotype and suggests that some patients diagnosed with pachyonychia may in fact be suffering from Clouston syndrome.

The molecular genetics of keratin disorders

Keratins are the type I and II intermediate filament proteins which form a cytoskeletal network within all epithelial cells. They are expressed in pairs in a tissue- and differentiation-specific fashion. Epidermolysis bullosa simplex (EBS) was the first human disorder to be associated with keratin mutations. The abnormal keratin filament aggregates observed in basal cell keratinocytes of some EBS patients are composed of keratins K5 and K14. Dominant mutations in the genes encoding these proteins were shown to disrupt the keratin filament cytoskeleton resulting in cells that are less resilient and blister with mild physical trauma. Identification of mutations in other keratin genes soon followed with attention focussed on disorders showing abnormal clumping of keratin filaments in specific cells. For example, in bullous congenital ichthyosiform erythroderma, clumping of filaments in the suprabasal cells led to the identification of mutations in the suprabasal keratins, K1 and K10. Mutations have now been identified in 18 keratins, all of which produce a fragile cell phenotype. These include ichthyosis bullosa of Siemens (K2e), epidermolytic palmoplantar keratoderma (K1, K9), pachyonychia congenita (K6a, K6b, K16, K17), white sponge nevus (K4, K13), Meesmann's corneal dystrophy (K3, K12), cryptogenic cirrhosis (K8, K18) and monilethrix (hHb6, hHb1).In general, these disorders are inherited as autosomal dominant traits and the mutations act in a dominant-negative manner. Therefore, treatment in the form of gene therapy is difficult, as the mutant gene needs to be inactivated. Ways of achieving this are actively being studied. Reliable mutation detection methods from genomic DNA are now available. This enables rapid screening of patients for keratin mutations. For some of the more severe phenotypes, prenatal diagnosis may be requested and this can now be performed from chorionic villus samples at an early stage of the pregnancy. This review article describes the discovery of, to date, mutations in 18 keratin genes associated with inherited human diseases.

Identification of a recurrent mutation in keratin 6a in a patient with overlapping clinical features of pachyonychia congenita types 1 and 2

Pachyonychia congenita is characterized by hypertrophic nail dystrophy and associated ectodermal features. PC-1 subtype is associated with mutations in keratins 6a or 16, whereas PC-2 subtype is linked to mutations in keratins 6b or 17. The correlation between the mutated gene and the type of PC has generally been consistent. In this report, we describe a case with overlapping clinical features of PC-1 and PC-2 in which a mutation in K6a was identified.