Connexins in epidermal health and diseases: insights into their mutations, implications, and therapeutic solutions

The epidermis, the outermost layer of the skin, serves as a protective barrier against external factors. Epidermal differentiation, a tightly regulated process essential for epidermal homeostasis, epidermal barrier formation and skin integrity maintenance, is orchestrated by several players, including signaling molecules, calcium gradient and junctional complexes such as gap junctions (GJs). GJ proteins, known as connexins facilitate cell-to-cell communication between adjacent keratinocytes. Connexins can function as either hemichannels or GJs, depending on their interaction with other connexons from neighboring keratinocytes. These channels enable the transport of metabolites, cAMP, microRNAs, and ions, including Ca2+, across cell membranes. At least ten distinct connexins are expressed within the epidermis and mutations in at least five of them has been linked to various skin disorders. Connexin mutations may cause aberrant channel activity by altering their synthesis, their gating properties, their intracellular trafficking, and the assembly of hemichannels and GJ channels. In addition to mutations, connexin expression is dysregulated in other skin conditions including psoriasis, chronic wound and skin cancers, indicating the crucial role of connexins in skin homeostasis. Current treatment options for conditions with mutant or altered connexins are limited and primarily focus on symptom management. Several therapeutics, including non-peptide chemicals, antibodies, mimetic peptides and allele-specific small interfering RNAs are promising in treating connexin-related skin disorders. Since connexins play crucial roles in maintaining epidermal homeostasis as shown with linkage to a range of skin disorders and cancer, further investigations are warranted to decipher the molecular and cellular alterations within cells due to mutations or altered expression, leading to abnormal proliferation and differentiation. This would also help characterize the roles of each isoform in skin homeostasis, in addition to the development of innovative therapeutic interventions. This review highlights the critical functions of connexins in the epidermis and the association between connexins and skin disorders, and discusses potential therapeutic options.

Identification of a founder variant AAGAB c.370C>T, p.Arg124Ter in patients with punctate palmoplantar keratoderma in Southern Denmark

Palmoplantar keratoderma (PPK) is a heterogeneous group of rare skin diseases characterized by hyperkeratosis on the palms or soles. The subtype isolated punctate PPK is caused by heterozygous variants in AAGAB. We investigated if the variant AAGAB c.370C>T, p.Arg124Ter in patients with punctate PPK in the Region of Southern Denmark represented a founder variant and estimated the age to the most recent common ancestor. We performed haplotype analysis on samples from 20 patients diagnosed with punctate PPK and the AAGAB c.370C>T, p.Arg124Ter variant. Using the Gamma Method, we calculated the years to the most recent common ancestor. We also explored the presence of the variant in other populations through literature and databases (HGMD, ClinVar, and gnomAD). Our analysis revealed a shared haplotype of 3.0 Mb, suggesting shared ancestry. The ancestral haplogroup was estimated to an age of 12.1 generations (CI: 4.9-20.3) equivalent to approximately 339 years (CI: 137-568). This study confirms that the frequently observed variant AAGAB c.370C>T, p.Arg124Ter in punctate PPK among patients in the Region of Southern Denmark is caused by a founder variant. We recommend testing for the variant as initial screening in our region and potentially for all Danish patients presenting with punctate PPK.

Pressure and Skin: A Review of Disease Entities Driven or Influenced by Mechanical Pressure

Skin perceives and reacts to external mechanical forces to create resistance against the external environment. Excessive or inappropriate stimuli of pressure may lead to cellular alterations of the skin and the development of both benign and malignant skin disorders. We conducted a comprehensive literature review to delve into the pressure-induced and aggravated skin disorders and their underlying pressure-related mechanisms. Dysregulated mechanical responses of the skin give rise to local inflammation, ischemia, necrosis, proliferation, hyperkeratosis, impaired regeneration, atrophy, or other injurious reactions, resulting in various disease entities. The use of personal devices, activities, occupations, weight bearing, and even unintentional object contact and postures are potential scenarios that account for the development of pressure-related skin disorders. The spectrum of these skin disorders may involve the epidermis (keratinocytes and melanocytes), hair follicles, eccrine glands, nail apparatuses, dermis (fibroblasts, mast cells, and vasculature), subcutis, and fascia. Clarifying the clinical context of each patient and recognizing how pressure at the cellular and tissue levels leads to skin lesions can enhance our comprehension of pressure-related skin disorders to attain better management.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Defective cathepsin Z affects EGFR expression and causes autosomal dominant palmoplantar keratoderma

BACKGROUND

The abnormal function of epidermal growth factor receptor (EGFR) has recently been shown to underlie various disorders of cornification.

OBJECTIVES

To delineate the genetic basis of a novel dominant form of palmoplantar keratoderma (PPK).

METHODS

Whole-exome (WES) and direct sequencing, quantitative real-time polymerase chain reaction, protein modelling, confocal immunofluorescence microscopy, immunoblotting, three-dimensional skin equivalents and an enzyme activity assay were used to delineate the genetic basis of a novel dominant form of PPK.

RESULTS

WES revealed heterozygous variants (c.274T > C and c.305C > T) in CTSZ (encoding cathepsin Z) in four individuals (belonging to three unrelated families) with focal PPK. Bioinformatics and protein modelling predicted the variants to be pathogenic. Previous studies have suggested that EGFR expression may be subject to cathepsin regulation. Immunofluorescence revealed reduced cathepsin Z expression in the upper epidermal layers and concomitant increased epidermal EGFR expression in patients harbouring CTSZ variants. Accordingly, human keratinocytes transfected with constructs expressing PPK-causing variants in CTSZ displayed reduced cathepsin Z enzymatic activity, as well as increased EGFR expression. In line with the role played by EGFR in the regulation of keratinocyte proliferation, human keratinocytes transfected with the PPK-causing variants showed significantly increased proliferation that was abolished upon exposure to erlotinib, an EGFR inhibitor. Similarly, downregulation of CTSZ resulted in increased EGFR expression and increased proliferation in human keratinocytes, suggestive of a loss-of-function effect of the pathogenic variants. Finally, three-dimensional organotypic skin equivalents grown from CTSZ-downregulated cells showed increased epidermal thickness and EGFR expression as seen in patient skin; here, too, erlotinib was found to rescue the abnormal phenotype.

CONCLUSIONS

Taken collectively, these observations attribute to cathepsin Z a hitherto unrecognized function in epidermal differentiation.

A Case Report of Hereditary Palmoplantar Keratoderma with Esophageal Melanosis

A 70-year-old man, a known case of diabetes mellitus since 10 years ago, presented with lower limb swelling and dyspnea on exertion for one month and dysphagia to solids associated with early satiety for 2 weeks. The patient had palmoplantar keratosis (PPK), which was present since birth with a similar family history. The patient was admitted to rule out esophageal malignancy. Upper gastrointestinal gastroscopy revealed esophagitis and esophageal melanosis with gastric mucosal erythema. Biopsies samples were taken. Histopathological examination revealed reflux esophagitis and chronic active Helicobacter pylori gastritis with no evidence of malignancy. His symptoms improved following H. pylori eradication and treatment for coronary artery disease and heart failure. The patient was advised of regular follow-up as he had risk factors for the development of esophageal melanoma or squamous cell carcinoma.

Main effects of retinol palmitate on skin structures and the technology of its use in dermatological practice

Vitamin A and its synthetic analogues are used in the treatment of numerous skin diseases. The main genomic effects of the natural form of vitamin A (retinol palmitate) are associated with its active metabolite all-trans-retinoic acid and are compensated by several restrictive mechanisms. Numerous studies have proved that retinol stimulates the proliferation of keratinocytes of the basal layer of the epidermis and endothelial cells, and also activates dermal fibroblasts to synthesize proteins of the extracellular matrix of the dermis. As a result, the thickening the epidermis, increases the mechanical strength of the skin and the hydrating ability of the dermis, angiogenesis increase. The ability of retinol to enhance the adhesion of endothelial cells and leukocytes, regulate the processes of keratinization and sebum secretion was found. Vitamin A is also a powerful antioxidant. Retinol palmitate is used as the main or auxiliary drug for the treatment of a wide range of dermatoses. The principle of application is based on clinical studies and confirmed by existing experimental data. In the treatment, the following algorithm is followed. If retinol palmitate is necessary to improve epithelialization and strengthen the epidermal barrier, medium therapeutic doses should be used. For the treatment of disorders of keratinization processes, depending on the severity of the pathological condition, medium and high therapeutic doses of the drug are used. Violation of the processes of sebum secretion and severe hyperkeratosis respond better to treatment at high therapeutic doses. It should be noted that many skins clinical manifestations mostly regress under the action of vitamin A in doses that do not lead to the appearance of signs of toxicity of the drug.

RSPO1-mutated keratinocytes from palmoplantar keratoderma display impaired differentiation, alteration of cell-cell adhesion, EMT-like phenotype and invasiveness properties: implications for squamous cell carcinoma susceptibility in patients with 46XX disorder of sexual development

Background

Secreted R-spondin (RSPO) proteins play a key role in reproductive organ development, epithelial stem cell renewal and cancer induction by reinforcing canonical Wnt signaling. We have previously reported that palmoplantar keratoderma (PPK), predisposition to cutaneous squamous cell carcinoma (SCC) development and sex reversal segregate as autosomal recessive trait in patients carrying RSPO1-mutations.

Although our previous findings suggested that RSPO1 secreted from fibroblasts regulates keratinocyte growth or differentiation, the role of this protein in the epidermis remains largely unexplored. Our study was aimed at expanding the phenotypic, molecular and functional characterization of RSPO1-mutated skin and keratinocytes.

Results

Cultured primary keratinocytes from PPK skin of a RSPO1-mutated XX-sex reversed patient displayed highly impaired differentiation and epithelial-mesenchymal transition (EMT)-like phenotype. Interestingly, RSPO1-mutated PPK skin expressed markers of increased proliferation, dedifferentiation and altered cell–cell adhesion. Furthermore, all these signs were more evident in SCC specimens of the patient. Cultured PPK patient’s keratinocytes exhibited increased expression of cell‒matrix adhesion proteins and extracellular matrix remodeling enzymes. Moreover, they showed invasiveness properties in an organotypic skin model in presence of PPK fibroblasts, which behave like cancer-associated fibroblasts. However, the co-culture with normal fibroblasts or treatment with the recombinant RSPO1 protein did not revert or reduce the EMT-like phenotype and invasion capability of PPK keratinocytes. Notably, RSPO1-mutated PPK fibroblasts induced a hyperproliferative and dedifferentiated phenotype of age-matched normal control plantar keratinocytes. Wnt signaling has a key role in both PPK promotion and SCC development. Accordingly, Wnt mediators were differentially expressed in both PPK keratinocytes and skin specimens of RSPO1-mutated patient compared to control.

Conclusions

Altogether our data indicate that the absence of RSPO1 in patients with 46XX disorder of sexual development affects the skin microenvironment and epidermal integrity, thus contributing to the risk of SCC tumorigenesis in palmoplantar regions exposed to major frictional stresses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02434-2.

Loss-of-function variants in KLF4 underlie autosomal dominant palmoplantar keratoderma

PURPOSE

Palmoplantar keratodermas (PPKs) form a group of disorders characterized by thickening of palm and sole skin. Over the past 2 decades, many types of inherited PPKs have been found to result from abnormal expression, processing, or function of adhesion proteins.

METHODS

We used exome and direct sequencing to detect causative pathogenic variants. Functional analysis of these variants was conducted using reverse transcription quantitative polymerase chain reaction, immunofluorescence confocal microscopy, immunoblotting, a promoter reporter assay, and chromatin immunoprecipitation.

RESULTS

We identified 2 heterozygous variants (c.1226A>G and c.633_634dupGT) in KLF4 in 3 individuals from 2 different unrelated families affected by a dominant form of PPK. Immunofluorescence staining for a number of functional markers revealed reduced epidermal DSG1 expression in patients harboring heterozygous KLF4 variants. Accordingly, human keratinocytes either transfected with constructs expressing these variants or downregulated for KLF4 displayed reduced DSG1 expression, which in turn has previously been found to be associated with PPK. A chromatin immunoprecipitation assay confirmed direct binding of KLF4 to the DSG1 promoter region. The ability of mutant KLF4 to transactivate the DSG1 promoter was significantly decreased when compared with wild-type KLF4.

CONCLUSION

Loss-of-function variants in KLF4 cause a novel form of dominant PPK and show its importance in the regulation of epidermal differentiation.

A novel desmoplakin mutation causes dilated cardiomyopathy with palmoplantar keratoderma as an early clinical sign

Background

PPKs represent a heterogeneous group of disorders with hyperkeratosis of palmar and/or plantar skin. PPK, hair shaft abnormalities, cardiomyopathy and arrhythmias can be caused by mutations in desmosomal genes, e.g. desmoplakin (DSP). PPK should trigger genetic testing to reveal mutations with possible related cardiac disease.

Objectives

To report a large multigenerational family with a novel DSP mutation associated with early‐onset PPK and adult‐onset cardiomyopathy and arrhythmias.

Methods

A custom‐designed in‐house panel of 35 PPK related genes was used to screen mutations in the index patient with focal PPK. The identified DSP mutation was verified by Sanger sequencing. DNA samples from 20 members of the large multigenerational family were sequenced for the DSP mutation. Medical records were reviewed. Clinical dermatological evaluation was performed, including light microscopy of hair samples. Cardiac evaluation included clinical examination, echocardiography, cardiac magnetic resonance imaging (CMR), electrocardiogram (ECG), Holter monitoring and laboratory tests.

Results

We identified a novel autosomal dominant truncating DSP c.2493delA p.(Glu831Aspfs*33) mutation associated with dilated cardiomyopathy (DCM) with arrhythmia susceptibility and focal PPK as an early cutaneous sign. The mutation was found in nine affected family members, but not in any unaffected members. Onset of dermatological findings preceded cardiac symptoms which were variable and occurred at adult age.

Conclusions

We report a novel truncating DSP mutation causing focal PPK with varying severity and left ventricular dilatation and ventricular extrasystoles. This finding emphasizes the importance of genetic diagnosis in patients with PPK for clinical counselling and management of cardiomyopathies and arrhythmias.

Structural and functional foot disorders in patients with genodermatoses: a single-centre, retrospective chart review

Background

Skin lesions on the feet and foot deformities impair daily activities and decrease quality of life. Although substantial foot deformities occur in many genodermatoses, few reports have been published on this topic. Therefore, we performed a retrospective chart review to identify patients with genodermatoses and foot disorders. We included 16 patients, who were investigated clinically and with molecular biology.

Results

The following genodermatoses with foot deformities were detected: autosomal recessive congenital ichthyosis (ARCI, n = 7); palmoplantar keratodermas (PPKs, n = 6); ichthyosis follicularis, atrichia, and photophobia (IFAP, n = 1); ectrodactyly-ectodermal dysplasia-clefting (EEC, n = 1); and ichthyosis with confetti (IWC, n = 1). Foot problems not only varied in severity depending on the disease but also showed phenotypic heterogeneity among patients with the same condition. Foot deformities were most pronounced in patients with EEC (split foot) or IWC (contractures) and less severe in those with ARCI (clawed toes), IFAP (hollow feet), or PPK (no bone abnormalities in the feet).

Conclusion

Because a range of distinct genodermatoses involve foot abnormalities, early rehabilitation and other corrective measures should be provided to patients with foot involvement to improve gait and prevent/delay irreversible complications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02207-x.

Five Functional Aspects of the Epidermal Barrier

The epidermis is a living, multilayered barrier with five functional levels, including a physical, a chemical, a microbial, a neuronal, and an immune level. Altogether, this complex organ contributes to protect the host from external aggression and to preserve its integrity. In this review, we focused on the different functional aspects.

The Effectiveness of Cochlear Implantation for Children of Hereditary Deafness: A Multicenter Retrospective Study

Aim

To study the effectiveness of cochlear implantation in deaf children with gene mutation.

Method

420 children from three medical centers with cochlear implants were selected. Before wearing the cochlear implant and 6 months after wearing the cochlear implant, the children's rehabilitation efficacy was evaluated through categories of auditory performance (CAP) and speech intelligibility rating (SIR). The SSF-MCDI and MUSS before and after the treatment were also compared.

Results

The CAP and SIR scores of the children after the intervention were higher than those before the intervention (P < 0.05). Univariate analysis found that the age of cochlear implantation, parents' education level, and monthly family income were all influencing factors of the CAP score of children with prelingual cochlear implantation (P < 0.05). Multivariate logistic regression analysis shows that the age of cochlear implantation <5 years, parents' education level, and monthly household income are all independent risks of CAP scores in children with prelingual deaf cochlear implantation. Univariate analysis found that the age of cochlear implantation, parents' education level, and monthly household income are all based on the SIR scores of children with prelingual cochlear implantation. Multivariate logistic regression analysis can be obtained: the age of cochlear implantation less than 5 years, the education level of parents, and the monthly family income are independent risk factors for SIR scores in children with prelingual deaf cochlear implantation (P < 0.05).

Conclusion

The rehabilitation effect of cochlear implants is significant, and the age of cochlear implantation, parents' education level, and monthly family income are all related factors that affect the rehabilitation effect.

The first case report of Haim Munk disease with neurological manifestations and literature review

HMS can have neurologic MS like manifestations. It is urgent to do more research and report probable unknown associations of HMS for its better management.

Hereditary palmoplantar keratoderma - phenotypes and mutations in 64 patients

BACKGROUND

Hereditary palmoplantar keratodermas (PPK) represent a heterogeneous group of rare skin disorders with epidermal hyperkeratosis of the palms and soles, with occasional additional manifestations in other tissues. Mutations in at least 69 genes have been implicated in PPK, but further novel candidate genes and mutations are still to be found.

OBJECTIVES

To identify mutations underlying PPK in a cohort of 64 patients.

METHODS

DNA of 48 patients was analysed on a custom-designed in-house panel for 35 PPK genes, and 16 patients were investigated by a diagnostic genetic laboratory either by whole-exome sequencing, gene panels or targeted single-gene sequencing.

RESULTS

Of the 64 PPK patients, 32 had diffuse (50%), 19 focal (30%) and 13 punctate (20%) PPK. None had striate PPK. Pathogenic mutations in altogether five genes were identified in 31 of 64 (48%) patients, the majority (22/31) with diffuse PPK. Of them, 11 had a mutation in AQP5, five in SERPINB7, four in KRT9 and two in SLURP1. AAGAB mutations were found in nine punctate PPK patients. New mutations were identified in KRT9 and AAGAB. No pathogenic mutations were detected in focal PPK. Variants of uncertain significance (VUS) in PPK-associated and other genes were observed in 21 patients that might explain their PPK. No suggestive pathogenic variants were found for 12 patients.

CONCLUSIONS

Diffuse PPK was the most common (50%) and striate PPK was not observed. We identified pathogenic mutations in 48% of our PPK patients, mainly in five genes: AQP5, AAGAB, KRT9, SERPINB7 and SLURP1.

Treatment of hereditary palmoplantar keratoderma: a review by analysis of the literature

BACKGROUND

No specific or curative therapy exists for hereditary palmoplantar keratoderma (hPPK), which can profoundly alter patient quality of life, leading sometimes to severe functional impairment and pain. The rarity and the aetiological diversity of this group of disorders can explain the difficulty in comparing the efficacy of available treatments.

OBJECTIVES

To review the different treatments tried in patients with hPPK since 2008, their efficacy and safety, with an evaluation of the various therapeutic modalities that can be used to treat hPPK.

METHODS

We undertook a comprehensive review of the literature data published since 2008.

RESULTS

Only a few case series and individual case reports were identified. Topical (emollients, keratolytics, retinoids, steroids) and systemic treatments (mostly different retinoids), often combined, are used to relieve symptoms. Oral retinoids appear to be the most efficient treatment, but not in all PPK forms, and with variable tolerance. New targeted treatments, according to the specific mechanisms of hPPK, appear promising for the future.

CONCLUSIONS

More studies using robust methodology and involving larger cohorts of well-characterized patients (phenotype-genotype) are necessary and should be prioritized by structured networks, such as the European Network for Rare Skin Diseases (ERN-Skin), with the aim of better management of patients with rare skin diseases.

Loss-of-Function Variants in SERPINA12 Underlie Autosomal Recessive Palmoplantar Keratoderma

Inherited palmoplantar keratodermas refer to a large and heterogeneous group of conditions resulting from abnormal epidermal differentiation and featuring thickening of the skin of the palms and soles. Here, we aimed at delineating the genetic basis of an autosomal recessive form of palmoplantar keratodermas manifesting with erythematous hyperkeratotic plaques over the palms and soles, extending to non-palmoplantar areas. Whole-exome sequencing in affected individuals revealed homozygous nonsense variants in the SERPINA12 gene. SERPINA12 encodes the visceral adipose tissue-derived serpin A12, a serine protease inhibitor. The pathogenic variants were found to result in reduced visceral adipose tissue-derived serpin A12 expression in patients' skin biopsies in comparison to healthy controls. In addition, SERPINA12 downregulation in three-dimensional skin equivalents was associated with marked epidermal acanthosis and hyperkeratosis, replicating the human phenotype. Moreover, decreased SERPINA12 expression resulted in reduced visceral adipose tissue-derived serpin A12-mediated inhibition of kallikrein 7 activity as well as decreased levels of desmoglein-1 and corneodesmosin, two known kallikrein 7 substrates, which are required for normal epidermal differentiation. The present data, taken collectively, demarcate a unique type of autosomal recessive palmoplantar keratodermas, attribute to visceral adipose tissue-derived serpin A12 a role in skin biology, and emphasize the importance of mechanisms regulating proteolytic activity for normal epidermal differentiation.

Palmoplantar keratoderma, oral involvement, and homozygous CTSC mutation in two brothers from Cambodia

Haim-Munk syndrome (HMS) and Papillon-Lefevre syndrome (PLS) are phenotypic variants of palmoplantar keratoderma (PPK) with progressive early-onset periodontitis and dental caries. HMS and PLS have been associated with homozygous or compound heterozygous mutations in the lysosomal protease gene Cathepsin C (CTSC). There have been only a few documented cases of CTSC mutations in patients from South-East Asia. We report the clinical findings of two Cambodian brothers who presented with diffuse, demarcated PPK with transgrediens extending to the elbows and knees, as well as pachyonychia and dental caries. Arachnodactyly and periodontitis were also found in the older brother. Next-generation sequencing unveiled a homozygous missense variant in CTSC (NM_001814.5: c.1337AC: p.(Asp446Ala)) in both brothers. Both parents were heterozygous for the variant, while an unaffected older brother was homozygous for the wild-type allele. Our study adds to the spectrum of mutations and associated clinical presentations for this rare genodermatosis.

[Acral melanoma in a patient with hereditary keratoderma of the palms and soles (mal de Meleda): A chance association?]

INTRODUCTION

Development of acral malignant melanoma in Mal de Meleda is highly unusual. As far as we could ascertain, to date, only 10 previous cases have been published. Herein, we report a new case.

OBSERVATION

A 64-year-old Algerian man was followed for familial Mal de Meleda. The diagnosis was based on clinical presentation as he had a non-syndromic hereditary foul-smelling and yellowish palmoplantar keratoderma transgrediens. After the failure of acitretin, which had not prevented retractile and mutilating progression of the palmoplantar keratoderma, he had undergone surgery with graft excision of both palms. At the age of 59 years, he presented a tumor on the dorsal aspect of the 1^st phalanx of the 3^rd finger of the right hand in a non-grafted area. The diagnosis of acral melanoma was confirmed histologically. The radiological findings showed a specific homolateral axillary adenopathy. He underwent digital amputation of the 3^rd finger, with lymph node dissection and chemotherapy involving dacarbazine. Follow-up at 5 years showed complete remission of the melanoma.

DISCUSSION

Mal de Meleda is a hereditary palmoplantar keratoderma due to mutation of the SLURP1 gene. Clinical diagnosis is based on the typical phenotype in adulthood. The occurrence of acral melanoma, which is a rare form of melanoma (1 to 7%), especially in the fingers, together with an unusual palmoplantar keratoderma in a subject of type IV phototype does not appear to be a chance event. This association seems to be the outcome of immune dysregulation rather than of chronic inflammation.

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.

Topical Selenium Sulfide for the Treatment of Hyperkeratosis

Hyperkeratosis presents as thickened skin. It can be congenital or acquired. Typically, it affects the palms and soles; the distribution of epidermal involvement is either diffuse, focal, or punctate. Microscopically, the pathologic signature of hyperkeratosis is marked orthokeratosis of the stratum corneum. Topical treatments provide the mainstay of therapy for hyperkeratosis. These include keratolytics (such as urea, salicylic acid, and lactic acid) and retinoids; physical debridement, topical corticosteroids, and phototherapy (using topical psoralen and ultraviolet A phototherapy) are other local therapeutic modalities. Selenium is a non-metallic essential element; its water-insoluble salt, selenium sulfide, is an active ingredient that is used (in either a foam, lotion, or shampoo) to treat not only seborrheic dermatitis but also tinea versicolor. Three individuals with hyperkeratosis involving their palms and/or soles are described; the hyperkeratosis was successful treated with topical selenium sulfide in either a 2.5% lotion/shampoo or a 2.75% foam. The response to topical selenium sulfide was not only rapid but also complete and sustained; none of the patients experienced any adverse events secondary to the therapy. In conclusion, we recommend that topical selenium sulfide be added to the therapeutic armamentarium for congenital or acquired hyperkeratosis—particularly for those patients with involvement of their palms and soles.