A review of the clinical phenotype of 254 patients with genetically confirmed pachyonychia congenita

A cross-sectional study of erythromelalgia in patients with pachyonychia congenita

Pachyonychia congenita (PC) is a rare genodermatosis characterized by focal palmoplantar keratoderma, severe plantar pain and dystrophic nails. Anecdotally, some patients with PC have erythematous soles and episodic burning plantar pain, indicative of secondary erythromelalgia. This study aimed to identify the prevalence and genetic predictors of erythromelalgia in PC.

Pain Hypersensitivity in SLURP1 and SLURP2 Knock-out Mouse Models of Hereditary Palmoplantar Keratoderma

SLURP1 and SLURP2 are both small secreted members of the Ly6/u-PAR family of proteins and are highly expressed in keratinocytes. Loss-of-function mutations in SLURP1 lead to a rare autosomal recessive palmoplantar keratoderma (PPK), Mal de Meleda (MdM), which is characterized by diffuse, yellowish palmoplantar hyperkeratosis. Some individuals with MdM experience pain in conjunction with the hyperkeratosis that has been attributed to fissures or microbial superinfection within the affected skin. By comparison, other hereditary PPKs such as pachyonychia congenita and Olmsted syndrome show prevalent pain in PPK lesions. Two mouse models of MdM, Slurp1 knock-out and Slurp2X knock-out, exhibit robust PPK in all four paws. However, whether the sensory experience of these animals includes augmented pain sensitivity remains unexplored. In this study, we demonstrate that both models exhibit hypersensitivity to mechanical and thermal stimuli as well as spontaneous pain behaviors in males and females. Anatomical analysis revealed slightly reduced glabrous skin epidermal innervation and substantial alterations in palmoplantar skin immune composition in Slurp2X knock-out mice. Primary sensory neurons innervating hindpaw glabrous skin from Slurp2X knock-out mice exhibit increased incidence of spontaneous activity and mechanical hypersensitivity both in vitro and in vivo. Thus, Slurp knock-out mice exhibit polymodal PPK-associated pain that is associated with both immune alterations and neuronal hyperexcitability and might therefore be useful for the identification of therapeutic targets to treat PPK-associated pain.

Walking a day in a pachyonychia congenita patient's shoes: Impact on plantar pain and activity levels measured with wristband activity trackers

Background Plantar keratoderma is a common finding in pachyonychia congenita, significantly impairing ambulation and quality of life. Due to the variation of pain reporting in pachyonychia congenita clinical studies, it is difficult to evaluate the efficacy of treatment outcomes for painful plantar keratodermas. Objectives To objectively analyse associations between plantar pain and activity levels in pachyonychia congenita patients using a wristband tracker. Methods Pachyonychia congenita patients and matched normal controls wore wristband activity trackers and completed a daily digital survey to record their highest and total pain scores (0-10 scale) each day for 28 consecutive days during four different seasons. Results Twenty four participants (12 pachyonychia congenita patients and 12 matched normal controls) completed the study. Pachyonychia congenita patients walked 1801.30 fewer steps/day (95% CI, -3666.4, 64.1) than normal controls (P = 0.072) and had greater average total [5.26; SD, 2.10] and highest (6.92; SD, 2.35) daily pain than normal controls [0.11 (SD, 0.47), 0.30 (SD, 0.22), respectively] (P < 0.001, both). On average, for each one unit increase in daily highest pain level, pachyonychia congenita activity decreased 71.54 steps/day (SE, 38.90, P = 0.066). Limitation The study had a small number of participants, limiting statistical power. Only pachyonychia congenita patients, ages 18 years or older, with keratin 6a, keratin 16, and keratin 17 mutations were included, limiting generalizability. Conclusion Pachyonychia congenita patients were less active with significantly higher pain than normal controls. There was an inverse correlation between pain and activity. Our findings suggest that wristband tracker technology may be used to evaluate treatment efficacy in future trials on severe plantar pain; therapeutic interventions that decrease plantar pain should correlate with significant increases in activity using wristband trackers.

Phenotype and genotype features of Vietnamese children with pachyonychia congenita

BACKGROUND

Pachyonychia congenita (PC) is a group of autosomal dominant disorders caused by mutations in one of five keratin genes (KRT6A, KRT6B, KRT6C, KRT16, or KRT17). PC is an extremely rare condition. To our knowledge, this is the largest genotype-phenotype study of PC in a Vietnamese population to date.

MATERIALS AND METHODS

We investigated keratin gene mutations and clinical features of seven Vietnamese children with PC.

RESULTS

The seven Vietnamese patients were from six different families (two patients in the same family) from across Northern, Central, and Southern Vietnam. All children displayed PC symptoms before 1 year of age, but diagnosis was delayed in 4/7 patients. Thick fingernails, thick toenails, oral leukokeratosis, and follicular hyperkeratosis were the most common features recorded by all seven patients. Plantar keratoderma and thick fingernails were the clinical features associated with the most significant effect on daily function. All patients had mutations in KRT6A (PC-K6a) focused on the 1A and 2B domains. We found three distinct types of mutations (K6a R466P, K6a N171K, and K6a N172del). One mutation (N172del) was common to 5/7 (71.4%) of the patients.

CONCLUSIONS

Individuals displaying nail dystrophy, oral leukokeratosis, follicular hyperkeratosis, and plantar keratoderma should be referred for genetic testing given the high likelihood of a PC-K6a-related mutation in patients with this constellation of clinical signs.

Coexistence of pachyonychia congenita and hidradenitis suppurativa: more than a coincidence

BACKGROUND

The coexistence of pachyonychia congenita (PC) and hidradenitis suppurativa (HS) has been described in case reports. However, the pathomechanism underlying this association and its true prevalence are unknown.

OBJECTIVES

To determine the genetic defect underlying the coexistence of PC and HS in a large kindred, to delineate a pathophysiological signalling defect jointly leading to both phenotypes, and to estimate the prevalence of HS in PC.

METHODS

We used direct sequencing and a NOTCH luciferase reporter assay to characterize the pathophysiological basis of the familial coexistence of HS and PC. A questionnaire was distributed to patients with PC registered with the International Pachyonychia Congenita Research Registry (IPCRR) to assess the prevalence of HS among patients with PC.

RESULTS

Direct sequencing of DNA samples obtained from family members displaying both PC and HS demonstrated a missense variant (c.275A>G) in KRT17, encoding keratin 17. Abnormal NOTCH signalling has been suggested to contribute to HS pathogenesis. Accordingly, the KRT17 c.275A>G variant resulted in a significant decrease in NOTCH activity. To ascertain the clinical importance of the association of HS with PC, we distributed a questionnaire to all patients with PC registered with the IPCRR. Seventy-two of 278 responders reported HS-associated clinical features (25·9%). Disease-causing mutations in KRT17 were most prevalent among patients with a dual phenotype of PC and HS (43%).

CONCLUSIONS

The coexistence of HS and KRT17-associated PC is more common than previously thought. Impaired NOTCH signalling as a result of KRT17 mutations may predispose patients with PC to HS. What is already known about this topic? The coexistence of pachyonychia congenita (PC) and hidradenitis suppurativa (HS) has been described in case reports. However, the pathomechanism underlying this association and its true prevalence are unknown. What does this study add? A dual phenotype consisting of PC and HS was found to be associated with a pathogenic variant in KRT17. This variant was found to affect NOTCH signalling, which has been previously implicated in HS pathogenesis. HS was found to be associated with PC in a large cohort of patients with PC, especially in patients carrying KRT17 variants, suggesting that KRT17 variants causing PC may also predispose to HS. What is the translational message? These findings suggest that patients with PC have a higher prevalence of HS than previously thought, and hence physicians should have a higher level of suspicion of HS diagnosis in patients with PC.

High-frequency ultrasound in clinical dermatology: a review

Background

Ultrasound was first introduced in clinical dermatology in 1979. Since that time, ultrasound technology has continued to develop along with its popularity and utility.

Main text summary

Today, high-frequency ultrasound (HFUS), or ultrasound using a frequency of at least 10 megahertz (MHz), allows for high-resolution imaging of the skin from the stratum corneum to the deep fascia. This non-invasive and easy-to-interpret tool allows physicians to assess skin findings in real-time, enabling enhanced diagnostic, management, and surgical capabilities. In this review, we discuss how HFUS fits into the landscape of skin imaging. We provide a brief history of its introduction to dermatology, explain key principles of ultrasonography, and review its use in characterizing normal skin, common neoplasms of the skin, dermatologic diseases and cosmetic dermatology.

Conclusion

As frequency advancements in ultrasonography continue, the broad applications of this imaging modality will continue to grow. HFUS is a fast, safe and readily available tool that can aid in diagnosing, monitoring and treating dermatologic conditions by providing more objective assessment measures.

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.

Identification of clinically useful predictive genetic variants in pachyonychia congenita

BACKGROUND

Pachyonychia congenita (PC) refers to a group of autosomal dominant disorders caused by mutations in five keratin genes (KRT16,KRT6A,KRT17,KRT6B or KRT6C). Current disease classification is based on the gene harbouring disease-causing variants.

AIMS

We harnessed the International Pachyonychia Congenita Research Registry (IPCRR) containing both clinical and molecular data on patients with PC worldwide, to identify genetic variants predicting disease severity.

METHODS

We ascertained 815 individuals harbouring keratin mutations registered in the IPCRR. We looked for statistically significant associations between genetic variants and clinical manifestations in a subgroup of patients carrying mutations found in at least 10% of the cohort. Data were analysed using χ² and Kruskal-Wallis tests.

RESULTS

We identified five mutations occurring in at least 10% of the patients registered in the IPCRR. The KRT16 p.L132P mutation was significantly associated with younger age of onset, presence of palmar keratoderma oral leucokeratosis and a higher number of involved nails. By contrast, the KRT16 p.N125S and p.R127C mutations resulted in a milder phenotype featuring a decreased number of involved nails and older age of onset. Patients carrying the p.N125S mutation were less likely to develop palmar keratoderma while p.R127C was associated with an older age of palmoplantar keratoderma onset. Moreover, the KRT17 p.L99P mutation resulted in an increased number of involved fingernails and patients demonstrating 20-nail dystrophy, while the opposite findings were observed with KRT17 p.N92S mutation.

CONCLUSIONS

We have identified novel and clinically useful genetic predictive variants in the largest cohort of patients with PC described to date.

Pediatric Nail Disorders

Many pediatric nail findings are normal variants and are no cause for alarm. Others represent congenital abnormalities or genetic syndromes for which there is no cure. Still others are inflammatory or infectious entities that require treatment. Pediatric nail disorders are reviewed, along with management.

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.

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.

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.

Genodermatoses with teeth abnormalities

Many genodermatoses exhibit abnormal teeth findings. Studies examining these entities are scarce and narrow in their scope. This paper reviews the evolution, development, and structure of the tooth and provides a summary of genodermatoses with aberrant dental findings. The latter are classified according to the abnormal dental findings: periodontal disease, anodontia/oligodontia/hypodontia, polydontia, enamel hypoplasia, natal teeth, dental pits, and others. Finally, we provide an algorithm that dermatologists and dentists can follow to better recognize genodermatoses with dental involvement.

The histopathological features of the nail plate in pachyonychia congenita

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant disorder of keratinization mediated by genetic mutations in KRT6A, KRT6B, KRT6C, KRT16, or KRT17. While nail dystrophy in PC has a significant impact on quality of life, the histopathological features of the nail plate in PC have not been previously reported. We report the histopathological features of nail plates provided by 19 patients with genetically confirmed PC.

METHODS

Nineteen patients with genetically confirmed PC provided a total of 56 nail plates for histopathologic examination. The nail plates were examined for the presence of hyphae, yeast, bacteria, neutrophils, parakeratosis, plasma globules, and hemorrhage. Specimens with onychomycosis (three patients) were excluded from the analysis.

RESULTS

No specific histopathological feature was identified in PC nails. Parakeratosis and plasma globules were the most prominent features in both clinically affected and unaffected PC nails. There was a significant association between clinical dystrophy of all 20 nails and KRT6A mutations, and a lack of dystrophy of all 20 nails in KRT6B mutations.

CONCLUSIONS

Parakeratosis and plasma globules in the absence of other inflammatory disorders should raise PC in the histopathologic differential diagnosis. The presence of onychomycosis in a nail plate does not exclude a diagnosis of PC.

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.

Follicular occlusion tetrad in a male patient with pachyonychia congenita: clinical and genetic analysis

The case of a 24-year-old male patient affected by follicular occlusion tetrad (acne conglobata, hidradenitis suppurativa, pilonidal cyst and dissecting cellulitis of the scalp) associated with clinical signs of pachyonychia congenita (PC)-2 (focal palmoplantar keratoderma, plantar pain, onycodystrophy and multiple cysts) is reported. The diagnosis was supported by genetic analysis that showed heterozygous mutation within the exon 1 of KRT17 gene. This case may reflect different expressions of a phenotypic spectrum induced by a common genetic alteration.

Hereditary Palmoplantar Keratoderma: A Practical Approach to the Diagnosis

The ridged skin of the palms and soles has several unique features: (i) presence of dermatoglyphics created by alternating ridges and grooves forming a unique pattern, (ii) presence of the highest density of eccrine sweat glands and absence of pilosebaceous units, and (iii) differential expression of keratins compared to the glabrous skin. These features explain the preferential localization of palmoplantar keratoderma (PPK) and several of its characteristic clinical features. PPK develops as a compensatory hyperproliferation of the epidermis and excessive production of stratum corneum in response to altered cornification of the palmoplantar skin due to mutations in the genes encoding several of the proteins involved in it. PPK can manifest as diffuse, focal, striate, or punctate forms per se or as a feature of several dermatological or systemic diseases. There is a wide genetic and phenotypic heterogeneity in hereditary PPK, due to which reaching an accurate diagnosis only on the basis of clinical features may be sometimes challenging for the clinicians in the absence of molecular studies. Nevertheless, recognizing the clinical patterns of keratoderma, extent of involvement, degree of mutilation, and associated appendageal and systemic involvement may help in delineating different forms. Molecular studies, despite high cost, are imperative for accurate classification, recognizing clinical patterns in resource poor settings is important for appropriate diagnosis, genetic counseling, and management. This review intends to develop a practical approach for clinical diagnosis of different types of hereditary PPK with reasonable accuracy.

Pachyonychia congenita: a case report of a successful treatment with rosuvastatin in a patient with a KRT6A mutation

Pachyonychia congenita (PC) is a rare autosomal dominant disorder characterized by nail dystrophy and palmoplantar keratoderma with severe plantar pain affecting quality of life. There is no effective treatment. Heterozygous mutations in the keratin genes KRT6A, KRT6B, KRT6C, KRT16 and KRT17 have been reported as a cause of PC. Herein we present a female patient with an amino acid substitution mutation in KRT6A (c.1381G>A, p.Glu461Lys in exon 7) and classic features of PC associated with oral leucokeratosis and follicular hyperkeratosis. We also demonstrate successful treatment of the patient with rosuvastatin. A 3.6-mm reduction in plantar callosity thickness was demonstrated by sonography. Our patient also experienced significant pain relief that allowed her to increase physical activity (Children's Dermatology Life Quality Index score dropped nine points following treatment). Collectively, these improvements suggest that rosuvastatin may offer a promising treatment for PC. What's already known about this topic? Pachyonychia congenita (PC) is an autosomal dominant disease characterized by nail dystrophy and painful plantar keratoderma. Keratolytics, emollients, retinoids and steroids have been used for treatment but with limited benefits. What does this study add? A patient with PC who had a KRT6A mutation was treated with rosuvastatin with significant improvement in plantar hyperkeratosis and pain. Statins could be a promising treatment for PC with long-term safety, but further studies are needed.

Nociceptin/orphanin FQ opioid peptide-receptor expression in pachyonychia congenita

Nociceptin/orphanin FQ opioid peptide (NOP)-receptor (NOP-R) is a member of the opioid receptor family. NOP-R activation has demonstrated analgesic effects in preclinical pain models without the addiction risks associated with other opiate targets. Pachyonychia congenita (PC) is a palmoplantar keratoderma characterized by neuropathic pain in affected skin. A cohort of KRT6A gene mutation PC patients with no other explanation for their neuropathic pain offered a unique opportunity to assess potential of NOP-R as a therapeutic target. Plantar biopsies from 10 PC patients and 10 age/gender matched controls were performed at the ball (PC-affected) and the arch (PC-unaffected) of the foot. NOP-R expression was assessed by immunohistochemistry. Localization of NOP-R in subsets of epidermal nerve fibers was investigated using the pan-neuronal marker PGP9.5, markers for unmyelinated peptidergic fibers (calcitonin gene-related peptide [CGRP] and substance P [SP]), as well as for myelinated Aδ and Aβ fibers (neurofilament H [NFH]). Robust NOP-R expression was detected in epidermal keratinocytes and in a subset of PGP9.5+ fibers in both epidermis and dermis, confirmed by western blot and absorption experiments with NOP-R peptide. NOP-R expression in keratinocytes was significantly reduced in PC-affected plantar skin compared with PC-unaffected skin. In addition, NOP-R expression occurred in dermal NFH+ myelinated fibers in all groups, although few CGRP+ fibers co-expressed NOP-R. Furthermore, most SP+ fibers also co-expressed NOP-R. These findings indicate that NOP-R is expressed on epidermal keratinocytes, as well as on epidermal and dermal nerve fibers and has potential as a promising target to treat neuropathic pain in PC.

Corneocyte proteomics: Applications to skin biology and dermatology

Advances in mass spectrometry-based proteomics now permit analysis of complex cellular structures. Application to epidermis and its appendages (nail plate, hair shaft) has revealed a wealth of information about their protein profiles. The results confirm known site-specific differences in levels of certain keratins and add great depth to our knowledge of site specificity of scores of other proteins, thereby connecting anatomy and pathology. An example is the evident overlap in protein profiles of hair shaft and nail plate, helping rationalize their sharing of certain dystrophic syndromes distinct from epidermis. In addition, interindividual differences in protein level are manifest as would be expected. This approach permits characterization of altered profiles as a result of disease, where the magnitude of perturbation can be quantified and monitored during treatment. Proteomic analysis has also clarified the nature of the isopeptide cross-linked residual insoluble material after vigorous extraction with protein denaturants, nearly intractable to analysis without fragmentation. These structures, including the cross-linked envelope of epidermal corneocytes, are comprised of hundreds of protein constituents, evidence for strengthening the terminal structure complementary to disulphide bonding. Along with other developing technologies, proteomic analysis is anticipated to find use in disease risk stratification, detection, diagnosis and prognosis after the discovery phase and clinical validation.

Chronic pain in pachyonychia congenita: evidence for neuropathic origin

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant skin disease, with chronic pain being the most prominent complaint. Histological studies showing alterations in sensory innervation, along with reports on alterations in mechanical sensitivity, suggest that PC may be a form of neuropathy.

OBJECTIVES

Here, for the first time, we aim to evaluate systematically the sensory function of patients with PC vs. controls, in order to investigate the pathophysiology of PC.

METHODS

Patients (n = 62) and controls (n = 45) completed the McGill and Douleur Neuropathique-4 (DN4) questionnaires. Sensory testing included detection and pain thresholds, pathological sensations, conditioned pain modulation (CPM) and temporal summation of pain.

RESULTS

A moderate-to-severe chronic pain in the feet, throbbing and stabbing in quality, was highly prevalent among patients with PC (86%) and was especially debilitating during weight bearing. In addition, the majority of patients had a DN4 score ≥ 4 (62%), static allodynia (55%) and tingling (53%) in the feet. Compared with controls, patients with PC exhibited thermal and mechanical hypoaesthesia and mechanical hyperalgesia in the feet. CPM was reduced among the patients, and was associated with more enhanced mechanical hyperalgesia in the feet. The specific gene and nature of the causative mutation did not affect any of these features.

CONCLUSIONS

Although thermal and mechanical hypoaesthesia may result from thicker skin, its presentation in painful regions, along with mechanical hyperalgesia and allodynia, point towards the possibility of neuropathic changes occurring in PC. The clinical features and DN4 scores support this possibility and therefore neuropathic pain medications may be beneficial for patients with PC.

Pachyonychia Congenita - Can a Specific Phenotype be a Clue to a Genetic Defect? - a Case Report and Literature Review

Pachyonychia congenita (PC) is a rare inherited disorder of keratinization characterized by hypertrophic nail dystrophy, painful palmoplantar blisters, cysts, follicular hyperkeratosis and oral leukokeratosis. These pathological clinical features are resulting from mutations in keratin proteins including KRT6A, KRT6B, KRT6C, KRT16, and KRT17. We present a 6-year-old girl with hypertrophic nail dystrophy, follicular hyperkeratosis, circumscribed plantar keratoderma and oral leukokeratosis. The features were consistent with the diagnosis of PC. The patient has been registered in the International Pachyonychia Congenita Research Registry (IPCRR) and is waiting for a detailed genetic analysis. The IPCRR has contributed to publication of numerous papers which emphasized the importance of the mutation type affecting various clinical presentations of PC. Based on recent data, a new classification system has been developed for PC, and it is gradually replacing the earlier classifications. It is based almost exclusively on the mutated genes. In this report we have raised the hypothesis that distinctive clinical features may be highly suggestive of a specific keratin mutation.

Implication of KRT16, FAM129A and HKDC1 genes as ATF4 regulated components of the integrated stress response

The ATF4 transcription factor is a key regulator of the adaptive integrated stress response (ISR) induced by various stresses and pathologies. Identification of novel transcription targets of ATF4 during ISR would contribute to the understanding of adaptive networks and help to identify novel therapeutic targets. We were previously searching for genes that display an inverse regulation mode by the transcription factors ATF4 and p53 in response to mitochondrial respiration chain complex III inhibition. Among the selected candidates the human genes for cytokeratine 16 (KRT16), anti-apoptotic protein Niban (FAM129A) and hexokinase HKDC1 have been found highly responsive to ATF4 overexpression. Here we explored potential roles of the induction of KRT16, FAM129A and HKDC1 genes in ISR. As verified by RT-qPCR, a dysfunction of mitochondrial respiration chain and ER stress resulted in a partially ATF4-dependent stimulation of KRT16, FAM129A and HKDC1 expression in the HCT116 colon carcinoma cell line. ISRIB, a specific inhibitor of ISR, was able to downregulate the ER stress-induced levels of KRT16, FAM129A and HKDC1 transcripts. An inhibition of ATF4 by RNAi attenuated the induction of KRT16, FAM129A and HKDC1 mRNAs in response to ER stress or to a dysfunctional mitochondrial respiration. The similar induction of the three genes was observed in another tumor-derived cervical carcinoma cell line HeLa. However, in HaCaT and HEK293T cells that display transformed phenotypes, but do not originate from patient-derived tumors, the ER stress-inducing treatments resulted in an upregulation of FAM129A and HKDC1, but not KRT16 transcripts, By a luciferase reporter approach we identified a highly active ATF4-responsive element within the upstream region of the KRT16 gene. The results suggest a conditional regulation of KRT16 gene by ATF4 that may be inhibited in normal cells, but engaged during cancer progression. Potential roles of KRT16, FAM129A and HKDC1 genes upregulation in adaptive stress responses and pathologies are discussed.

Peripheral neuropathic changes in pachyonychia congenita

We compared patterns of intraepidermal nerve fibers and mechanoreceptors from affected and unaffected plantar skin from patients with pachyonychia congenita (PC) and control subjects. Plantar biopsies from 10 genetically confirmed patients with PC (with a mutation in KRT6A) were performed at the ball of the foot (affected skin) and the arch (unaffected) and were compared to biopsies from corresponding locations in 10 control subjects. Tissue was processed to visualize intraepidermal nerve fibers (IENF) (PGP9.5), subsets of IENF (CGRP, substance P, tyrosine hydroxylase), myelinated nerve fiber (neurofilament H, NFH), blood vessels (CD31), Meissner corpuscles, and Merkel cells (MCs). Structures were quantified using stereology or validated quantification methods. We observed that PC-affected plantar skin had significantly lower sweat gland innervation (sweat gland nerve fiber density) and reduced numbers of Meissner corpuscles compared to PC-unaffected or anatomically matched control skin. In contrast, Merkel cell densities and blood vessel counts were higher in PC-affected skin compared to either control or PC-unaffected skin. There were no differences in myelinated nerve fiber densities, SP, or CGRP between the groups. Pressure pain thresholds in PC-affected skin were lower compared to PC-unaffected and anatomically matched control skin. Additionally, MC densities in callused plantar skin from healthy runners with callus and one subject with a nonpainful palmoplantar keratoderma (AQP5 mutation) were similar to PC-unaffected and control skin consistent with callus alone not being sufficient to increase MC number. These findings suggest that alterations in PC extend beyond keratinocytes and may provide strategies to study neuropathic pain in PC.

Management of Plantar KeratodermasLessons from Pachyonychia Congenita

Plantar keratodermas can arise due to a variety of genetically inherited mutations. The need to distinguish between different plantar keratoderma disorders is becoming increasingly apparent because there is evidence that they do not respond identically to treatment. Diagnosis can be aided by observation of other clinical manifestations, such as palmar keratoderma, more widespread hyperkeratosis of the epidermis, hair and nail dystrophies, or erythroderma. However, there are frequent cases of plantar keratoderma that occur in isolation. This review focuses on the rare autosomal dominant keratin disorder pachyonychia congenita, which presents with particularly painful plantar keratoderma for which there is no specific treatment. Typically, patients regularly trim/pare/file/grind their calluses and file/grind/clip their nails. Topical agents, including keratolytics (eg, salicylic acid, urea) and moisturizers, can provide limited benefit by softening the skin. For some patients, retinoids help to thin calluses but may lead to increased pain. This finding has stimulated a drive for alternative treatment options, from gene therapy to alternative nongenetic methods that focus on novel findings regarding the pathogenesis of pachyonychia congenita and the function of the underlying genes.

Proteomic profiling of Pachyonychia congenita plantar callus

Callus samples from the ball and the arch of the foot, collected on tape circles, were compared by shotgun proteomic profiling. Pachyonychia congenita subjects were sampled who exhibited a mutation in KRT6A, KRT6B, KRT6C, KRT16 or KRT17, and the proteins were digested and analyzed by tandem mass spectrometry. In comparison with samples from unaffected control subjects, those from subjects with KRT6A or KRT16 mutations displayed the most differences in profile from normal, while those from subjects with KRT6C or KRT17 mutations showed few differences from normal. The profiles from subjects with KRT6B mutations were intermediate in protein profile differences. Degree of departure from the normal profile could be estimated by expression of numerous proteins in callus from the ball of the foot that were consistently different. By contrast, the protein profile from the arch of the foot was hardly affected. The results provide a foundation for noninvasive monitoring of the efficacy of treatments with quantitative assessment of departure from the normal phenotype.

SIGNIFICANCE

Pachyonychia congenita is an orphan disease in which the connection between the basic defect (keratin mutation) and debilitating symptoms (severe plantar pain) is poorly understood. Present work addresses the degree to which the protein profile is altered in the epidermis where the severe pain originates. The results indicate that the mutated keratins differ greatly in the degree to which they elicit perturbations in protein profile. In those cases with markedly altered protein levels, monitoring the callus profile may provide an objective measure of treatment efficacy.

Report of the 13th Annual International Pachyonychia Congenita Consortium Symposium

The International Pachyonychia Congenita Consortium (IPCC) is a group of physicians and scientists from around the world dedicated to developing therapies for pachyonychia congenita, a rare autosomal dominant skin disorder. The research presented at the 13th Annual Research Symposium of the IPCC, held on 10-11 May 2016, in Scottsdale, AZ, U.S.A., is reported here.

Hereditary palmoplantar keratoderma "clinical and genetic differential diagnosis"

Hereditary palmoplantar keratoderma (PPK) is a heterogeneous group of disorders characterized by hyperkeratosis of the palm and the sole skin. Hereditary PPK are divided into four groups--diffuse, focal, striate and punctate PPK--according to the clinical patterns of the hyperkeratotic lesions. Each group includes simple PPK, without associated features, and PPK with associated features, such as involvement of nails, teeth and other organs. PPK have been classified by a clinically based descriptive system. In recent years, many causative genes of PPK have been identified, which has confirmed and/or rearranged the traditional classifications. It is now important to diagnose PPK by a combination of the traditional morphological classification and genetic testing. In this review, we focus on PPK without associated features and introduce their morphological features, genetic backgrounds and new findings from the last decade.

Keratin 17 Mutations in Four Families from India with Pachyonychia Congenita

Pachyonychia congenita (PC) is a rare autosomal dominant genetic skin disorder due to a mutation in any one of the five keratin genes, KRT6A, KRT6B, KRT6C, KRT16, or KRT17. The main features are palmoplantar keratoderma, plantar pain, and nail dystrophy. Cysts of various types, follicular hyperkeratosis, oral leukokeratosis, hyperhidrosis, and natal teeth may also be present. Four unrelated Indian families presented with a clinical diagnosis of PC. This was confirmed by genetic testing; mutations in KRT17 were identified in all affected individuals.

Laryngeal manifestations of pachyonychia congenita: a clinical case and discussion on management for the otolaryngologist

BACKGROUND

Pachyonychia congenita is a rare keratinising disorder, which typically presents during the first three years of life and usually affects the nails and palmoplantar surfaces. It can involve the larynx and potentially result in life-threatening airway obstruction.

METHODS

A case report is presented and the findings of a literature review are reported. The review involved a PubMed search using the keywords 'pachyonychia congenita' together with 'larynx', 'laryngeal involvement', 'laryngeal obstruction', 'airway obstruction', 'hoarseness' and/or 'stridor'.

RESULTS

A five-year-old boy, with confirmed pachyonychia congenita, presented with complications of laryngeal involvement over a four-year period. He required three intubations and a tracheostomy for acute airway obstruction. Treatment with potassium titanyl phosphate laser laryngoscopy stabilised the progression of laryngeal disease.

CONCLUSION

Patients with pachyonychia congenita and laryngeal involvement can have a varied presentation, ranging from hoarseness to acute airway obstruction. Management can be a challenge, requiring early evaluation, regular surveillance and aggressive treatment. This paper reports our experience in managing and treating the laryngeal complications of a child with pachyonychia congenita.