Palmoplantar keratodermas: clinical and genetic aspects

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.

A Rare Case on Capecitabine Induced Acquired Palmoplantar Keratoderma

Acquired palmoplantar keratoderma (PPK) is a non-hereditary hyperkeratosis of the palms and soles that is caused by various factors, including chemotherapeutic agents. The purpose of this case report is to present a rare case of acquired PPK caused by the chemotherapeutic agent capecitabine. A 54-year-old female complained of painful erythematous plaques on her palms and soles with history of consuming capecitabine. Physical examination revealed scaly erythematous plaques on the palmoplantar surface and knuckle pads on both hands. Histopathological features showed hyperkeratosis, acanthosis, vasodilatation, and perivascular lymphocytic infiltration. Therefore, the patient was diagnosed with acquired PPK due to capecitabine. The dose of capecitabine was reduced and the patient was administered topical corticosteroid and emollient. Improvement of skin lesions was strongly observed after discontinuation of capecitabine. The underlying cause of PPK should be identified to determine the appropriate treatment. Dose reduction or drug discontinuation is the mainstay therapy for patients with acquired PPK caused by chemotherapeutic agents.

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.

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.

Transcriptome Analysis of Host Inflammatory Responses to the Ectoparasitic Mite Sarcoptes scabiei var. hominis

Scabies, a human skin infestation caused by the ectoparasitic mite Sarcoptes scabiei var. hominis, affects more than 200 million people globally. The prevailing knowledge of the disease process and host immune response mechanisms is limited. A better understanding of the host-parasite relationship is essential for the identification of novel vaccine and drug targets. Here we aimed to interrogate the transcriptomic profiles of mite-infested human skin biopsies with clinical manifestations of ordinary scabies subjects ("OS"; n = 05) and subjects naive to scabies ("control"; n = 03) using RNASeq data analysis. A combined clustering, network, and pathway mapping approach enabled us to identify key signaling events in the host immune and pro-inflammatory responses to S. scabiei infestation. The clustering patterns showed various differentially expressed genes including inflammatory responses and innate immunity genes (DEFB4A, IL-19, CXCL8, CSF3, SERPINB4, S100A7A, HRNR) and notably upregulation of the JAK-STAT pathway in scabies-infested samples. Mite-infested human skin biopsies (GSE178563) were compared with an ex-vivo porcine infested model (E-MTAB-6433) and human skin equivalents (GSE48459). Marked enrichment of immune response pathways (JAK-STAT signaling, IL-4 and IL-13 pathway, and Toll receptor cascade), chemokine ligands and receptors (CCL17, CCL18, CCL3L1, CCL3L3, CCR7), and cytokines (IL-13 and IL-20) were observed. Additionally, genes known for their role in psoriasis and atopic dermatitis were upregulated, e.g., IL-19. The detailed transcriptomic profile has provided an insight into molecular functions, biological processes, and immunological responses and increased our understanding about transcriptomic regulation of scabies in human.

Palmo-plantar hyperkeratosis associated with HTLV-1 infection: a case report

Background

Palmoplantar hyperkeratosis is a cutaneous manifestation that had not been clearly associated with infection by the human T-cell lymphotropic virus, which is a retrovirus that in most cases does not develop clinical pathologies and its symptoms may be undetected. The skin is one of the most affected organs, however until now only seborrheic dermatitis, xerosis/ichthyosis and infective dermatitis associated with HTLV-1 have been described as cutaneous clinical manifestations of this disease.

Case presentation

We present the case of a 36-year-old male patient with serologically documented HTLV-1 infection, who presented symptoms of diarrhea, malabsorption due to Strongyloides stercoralis, and in whom a physical examination revealed an association with generalized xerosis and palmoplantar keratoderma confirmed by skin biopsy. Other infectious etiologies and malignancy were ruled out. This clinical manifestation was managed with dermal hydration, and skin care which improved the thickened skin and make it less noticeable.

Conclusions

According to our experience, this is the first reported case of palmoplantar keratoderma associated with a human lymphotropic virus infection. This is a skin manifestation that has not been confirmed in conjunction with HTLV-I before. This implies that palmoplantar keratoderma is a new clinical manifestation of this infection, that should be considered in the initial approach of patients in endemic areas with these dermatological characteristics.

Experimental Models for the Study of Hereditary Cornification Defects

Ichthyoses comprise a broad spectrum of keratinization disorders due to hereditary defects of cornification. Until now, mutations in more than 50 genes, mostly coding for structural proteins involved in epidermal barrier formation, have been identified as causes for different types of these keratinization disorders. However, due to the high heterogeneity and difficulties in the establishment of valid experimental models, research in this field remains challenging and translation of novel findings to clinical practice is difficult. In this review, we provide an overview of existing models to study hereditary cornification defects with focus on ichthyoses and palmoplantar keratodermas.

Gene editing in dermatology: Harnessing CRISPR for the treatment of cutaneous disease

The discovery of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system has revolutionized gene editing research. Through the repurposing of programmable RNA-guided CRISPR-associated (Cas) nucleases, CRISPR-based genome editing systems allow for the precise modification of specific sites in the human genome and inspire novel approaches for the study and treatment of inherited and acquired human diseases. Here, we review how CRISPR technologies have stimulated key advances in dermatologic research.  We discuss the role of CRISPR in genome editing for cutaneous disease and highlight studies on the use of CRISPR-Cas technologies for genodermatoses, cutaneous viruses and bacteria, and melanoma. Additionally, we examine key limitations of current CRISPR technologies, including the challenges these limitations pose for the widespread therapeutic application of CRISPR-based therapeutics.

A DSG1 Frameshift Variant in a Rottweiler Dog with Footpad Hyperkeratosis

A single male Rottweiler dog with severe footpad hyperkeratosis starting at an age of eight weeks was investigated. The hyperkeratosis was initially restricted to the footpads. The footpad lesions caused severe discomfort to the dog and had to be trimmed under anesthesia every 8–10 weeks. Histologically, the epidermis showed papillated villous projections of dense keratin in the stratum corneum. Starting at eight months of age, the patient additionally developed signs consistent with atopic dermatitis and recurrent bacterial skin and ear infections. Crusted hyperkeratotic plaques developed at sites of infection. We sequenced the genome of the affected dog and compared the data to 655 control genomes. A search for variants in 32 candidate genes associated with human palmoplantar keratoderma (PPK) revealed a single private protein-changing variant in the affected dog. This was located in the DSG1 gene encoding desmoglein 1. Heterozygous monoallelic DSG1 variants have been reported in human patients with striate palmoplantar keratoderma I (SPPK1), while biallelic DSG1 loss of function variants in humans lead to a more pronounced condition termed severe dermatitis, multiple allergies, and metabolic wasting (SAM) syndrome. The identified canine variant, DSG1:c.2541_2545delGGGCT, leads to a frameshift and truncates about 20% of the coding sequence. The affected dog was homozygous for the mutant allele. The comparative data on desmoglein 1 function in humans suggest that the identified DSG1 variant may have caused the footpad hyperkeratosis and predisposition for allergies and skin infections in the affected dog.

Gene editing in dermatology: Harnessing CRISPR for the treatment of cutaneous disease

The discovery of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system has revolutionized gene editing research. Through the repurposing of programmable RNA-guided CRISPR-associated (Cas) nucleases, CRISPR-based genome editing systems allow for the precise modification of specific sites in the human genome and inspire novel approaches for the study and treatment of inherited and acquired human diseases. Here, we review how CRISPR technologies have stimulated key advances in dermatologic research.  We discuss the role of CRISPR in genome editing for cutaneous disease and highlight studies on the use of CRISPR-Cas technologies for genodermatoses, cutaneous viruses and bacteria, and melanoma. Additionally, we examine key limitations of current CRISPR technologies, including the challenges these limitations pose for the widespread therapeutic application of CRISPR-based therapeutics.

Pathogenic FAM83G palmoplantar keratoderma mutations inhibit the PAWS1:CK1α association and attenuate Wnt signalling

Background: Two recessive mutations in the FAM83G gene, causing A34E and R52P amino acid substitutions in the DUF1669 domain of the PAWS1 protein, are associated with palmoplantar keratoderma (PPK) in humans and dogs respectively. We have previously reported that PAWS1 associates with the Ser/Thr protein kinase CK1α through the DUF1669 domain to mediate canonical Wnt signalling. Methods: Co-immunoprecipitation was used to investigate possible changes to PAWS1 interactors caused by the mutations. We also compared the stability of wild-type and mutant PAWS1 in cycloheximide-treated cells. Effects on Wnt signalling were determined using the TOPflash luciferase reporter assay in U2OS cells expressing PAWS1 mutant proteins. The ability of PAWS1 to induce axis duplication in Xenopus embryos was also tested. Finally, we knocked-in the A34E mutation at the native gene locus and measured Wnt-induced AXIN2 gene expression by RT-qPCR. Results: We show that these PAWS1 ^A34E and PAWS1 ^R52P mutants fail to interact with CK1α but, like the wild-type protein, do interact with CD2AP and SMAD1. Like cells carrying a PAWS1 ^F296A mutation, which also abolishes CK1α binding, cells carrying the A34E and R52P mutants respond poorly to Wnt signalling to an extent resembling that observed in FAM83G gene knockout cells. Consistent with this observation, these mutants, in contrast to the wild-type protein, fail to induce axis duplication in Xenopus embryos. We also found that the A34E and R52P mutant proteins are less abundant than the native protein and appear to be less stable, both when overexpressed in FAM83G-knockout cells and when knocked-in at the native FAM83G locus. Ala ³⁴ of PAWS1 is conserved in all FAM83 proteins and mutating the equivalent residue in FAM83H (A31E) also abolishes interaction with CK1 isoforms. Conclusions: We propose that mutations in PAWS1 cause PPK pathogenesis through disruption of the CK1α interaction and attenuation of Wnt signalling.

Novel nonsense variants in SLURP1 and DSG1 cause palmoplantar keratoderma in Pakistani families

Background

Inherited palmoplantar keratodermas (PPKs) are clinically and genetically heterogeneous and phenotypically diverse group of genodermatoses characterized by hyperkeratosis of the palms and soles. More than 20 genes have been reported to be associated with PPKs including desmoglein 1 (DSG1) a key molecular component for epidermal adhesion and differentiation. Mal de Meleda (MDM) is a rare inherited autosomal recessive genodermatosis characterized by transgrediens PPK, associated with mutations in the secreted LY6/PLAUR domain containing 1 (SLURP1) gene.

Methods

This study describes clinical as well as genetic whole exome sequencing (WES) and di-deoxy sequencing investigations in two Pakistani families with a total of 12 individuals affected by PPK.

Results

WES identified a novel homozygous nonsense variant in SLURP1, and a novel heterozygous nonsense variant in DSG1, as likely causes of the conditions in each family.

Conclusions

This study expands knowledge regarding the molecular basis of PPK, providing important information to aid clinical management in families with PPK from Pakistan.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0872-1) contains supplementary material, which is available to authorized users.

Exome sequencing identifies a KRT9 pathogenic variant in a Chinese pedigree with epidermolytic palmoplantar keratoderma

Background

Epidermolytic palmoplantar keratoderma (EPPK) is a rare skin disorder and its pathogenesis and inheritability are unknown.

Objective

To investigate the inheritance and pathogenesis of EPPK.

Methods

Two EPPK cases occurred in a three‐generation Chinese family. Patient–parents trio EPPK was carried out and the identified candidate variants were confirmed by Sanger sequencing.

Results

A heterozygous missense pathogenic variant, c.488G > A (p.Arg163Gln), in the keratin (KRT) 9 gene was detected in the proband and his son via targeted exome sequencing, and then validated by Sanger sequencing. This pathogenic variant cosegregated with the EPPK in extended family members, and was predicted to be pathogenic by SIFT, PolyPhen2, PROVEAN, and Mutation Taster. This heterozygous variation was not evident in 100 healthy controls.

Conclusion

This report describes a KRT9 c.488G > A (p.Arg163Gln) variant causing a diffuse phenotype of Chinese EPPK. The current results broaden the spectrum of KRT9 pathogenic variants responsible for EPPK and have important implications for molecular diagnosis, treatment, and genetic counseling for this family.

The desmosome is a mesoscale lipid raft-like membrane domain

Desmogleins (Dsgs) are cadherin family adhesion molecules essential for epidermal integrity. Previous studies have shown that desmogleins associate with lipid rafts, but the significance of this association was not clear. Here, we report that the desmoglein transmembrane domain (TMD) is the primary determinant of raft association. Further, we identify a novel mutation in the DSG1 TMD (G562R) that causes severe dermatitis, multiple allergies, and metabolic wasting syndrome. Molecular modeling predicts that this G-to-R mutation shortens the DSG1 TMD, and experiments directly demonstrate that this mutation compromises both lipid raft association and desmosome incorporation. Finally, cryo-electron tomography indicates that the lipid bilayer within the desmosome is ∼10% thicker than adjacent regions of the plasma membrane. These findings suggest that differences in bilayer thickness influence the organization of adhesion molecules within the epithelial plasma membrane, with cadherin TMDs recruited to the desmosome via the establishment of a specialized mesoscale lipid raft-like membrane domain.

Pathogenic FAM83G palmoplantar keratoderma mutations inhibit the PAWS1:CK1α association and attenuate Wnt signalling

Background: Two recessive mutations in the FAM83G gene, causing A34E and R52P amino acid substitutions in the DUF1669 domain of the PAWS1 protein, are associated with palmoplantar keratoderma (PPK) in humans and dogs respectively. We have previously reported that PAWS1 associates with the Ser/Thr protein kinase CK1α through the DUF1669 domain to mediate canonical Wnt signalling. Methods: Co-immunoprecipitation was used to investigate possible changes to PAWS1 interactors caused by the mutations. We also compared the stability of wild-type and mutant PAWS1 in cycloheximide-treated cells. Effects on Wnt signalling were determined using the TOPflash luciferase reporter assay in U2OS cells expressing PAWS1 mutant proteins. The ability of PAWS1 to induce axis duplication in Xenopus embryos was also tested. Finally, we knocked-in the A34E mutation at the native gene locus and measured Wnt-induced AXIN2 gene expression by RT-qPCR. Results: We show that these PAWS1 ^A34E and PAWS1 ^R52P mutants fail to interact with CK1α but, like the wild-type protein, do interact with CD2AP and SMAD1. Like cells carrying a PAWS1 ^F296A mutation, which also abolishes CK1α binding, cells carrying the A34E and R52P mutants respond poorly to Wnt signalling to an extent resembling that observed in FAM83G gene knockout cells. Consistent with this observation, these mutants, in contrast to the wild-type protein, fail to induce axis duplication in Xenopus embryos. We also found that the A34E and R52P mutant proteins are less abundant than the native protein and appear to be less stable, both when overexpressed in FAM83G-knockout cells and when knocked-in at the native FAM83G locus. Ala ³⁴ of PAWS1 is conserved in all FAM83 proteins and mutating the equivalent residue in FAM83H (A31E) also abolishes interaction with CK1 isoforms. Conclusions: We propose that mutations in PAWS1 cause PPK pathogenesis through disruption of the CK1α interaction and attenuation of Wnt signalling.

Palmoplantar Keratoderma with Keratoconus

Palmoplantar keratodermas (PPKs) are a rare heterogeneous group of disorders characterized by abnormal thickening of the skin of palms and soles. Ocular manifestations reported with palmer planter keratosis include scleral melanosis, macular deposits, and congenital cataract. We report, for the first time, a case of bilateral keratoconus in a patient with PPK.

CRISPR/Cas9-Mediated Treatment Ameliorates the Phenotype of the Epidermolytic Palmoplantar Keratoderma-like Mouse

CRISPR/Cas9 has been confirmed as a distinctly efficient, simple-to-configure, highly specific genome-editing tool that has been used to treat monogenetic disorders. Epidermolytic palmoplantar keratoderma (EPPK) is a common autosomal dominant keratin disease resulting from dominant-negative mutation of the KRT9 gene, and it has no effective therapy. We performed CRISPR/Cas9-mediated treatment on a knockin (KI) transgenic mouse model that carried a small indel heterozygous mutation of Krt9, c.434delAinsGGCT (p.Tyr144delinsTrpLeu), which caused a humanized EPPK-like phenotype. The mutation within exon 1 of Krt9 generated a novel protospacer adjacent motif site, TGG, for Cas9 recognition and cutting. By delivering lentivirus vectors (LVs) encoding single-guide RNAs (sgRNAs) and Cas9 that targeted Krt9 sequence into HeLa cells engineered to constitutively express wild-type and mutant keratin 9 (K9), we found the sgRNA was highly effective in reducing expression of the mutant K9 protein in vitro. We injected the LV into the fore-paws of adult KI-Krt9 mice three times every 8 days and found that the expression of K9 decreased ∼14.6%. The phenotypic mitigation was revealed by restoration of the abnormal differentiation and aberrant proliferation of the epidermis. Our data are the first to show that CRISPR/Cas9 is a potentially powerful therapeutic option for EPPK and other PPK subtypes.

Autosomal Recessive Keratoderma-Ichthyosis-Deafness (ARKID) Syndrome Is Caused by VPS33B Mutations Affecting Rab Protein Interaction and Collagen Modification

In this paper, we report three patients with severe palmoplantar keratoderma associated with ichthyosis and sensorineural deafness. Biallelic mutations were found in VPS33B, encoding VPS33B, a Sec1/Munc18 family protein that interacts with Rab11a and Rab25 proteins and is involved in trafficking of the collagen-modifying enzyme LH3. Two patients were homozygous for the missense variant p.Gly131Glu, whereas one patient was compound heterozygous for p.Gly131Glu and the splice site mutation c.240-1G>C, previously reported in patients with arthrogryposis renal dysfunction and cholestasis syndrome. We demonstrated the pathogenicity of variant p.Gly131Glu by assessing the interactions of the mutant VPS33B construct and its ability to traffic LH3. Compared with wild-type VPS33B, the p.Gly131Glu mutant VPS33B had reduced coimmunoprecipitation and colocalization with Rab11a and Rab25 and did not rescue LH3 trafficking. Confirming the cell-based experiments, we found deficient LH3-specific collagen lysine modifications in patients' urine and skin fibroblasts. Additionally, the epidermal ultrastructure of the p.Gly131Glu patients mirrored defects in tamoxifen-inducible VPS33B-deficient Vps33bfl/fl-ERT2 mice. Both patients and murine models revealed an impaired epidermal structure, ascribed to aberrant secretion of lamellar bodies, which are essential for epidermal barrier formation. Our results demonstrate that p.Gly131Glu mutant VPS33B causes an autosomal recessive keratoderma-ichthyosis-deafness syndrome.