Functional Analysis of a Novel Connexin30 Mutation in a Large Family with Hearing Loss, Pesplanus, Ichthyosis, Cutaneous Nodules, and Keratoderma.

Mutations in the gap-junction gene Cx30 (Connexin30, GJB6) are a known cause of hearing loss. Here, we report our findings on a large multigeneration family in which severe to profound sensorineural hearing impairment is associated with a variety of skin-related anomalies. Genome-wide analysis of the family showed that the locus maps to chromosome region 13ptel-q12.1 and that a novel mutation, p.N54K, in Cx30, cosegregates with the phenotype. Unlike wild-type Cx30, p.N54K Cx30 is predominantly localized in the cytoplasm and does not permit transfer of neurobiotin, suggesting improper cellular localization and abolishment of gap-junction activity.

Mutations in AQP5, encoding a water-channel protein, cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma.

Autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma is characterized by the adoption of a white, spongy appearance of affected areas upon exposure to water. After exome sequencing, missense mutations were identified in AQP5, encoding water-channel protein aquaporin-5 (AQP5). Protein-structure analysis indicates that these AQP5 variants have the potential to elicit an effect on normal channel regulation. Immunofluorescence data reveal the presence of AQP5 at the plasma membrane in the stratum granulosum of both normal and affected palmar epidermis, indicating that the altered AQP5 proteins are trafficked in the normal manner. We demonstrate here a role for AQP5 in the palmoplantar epidermis and propose that the altered AQP5 proteins retain the ability to form open channels in the cell membrane and conduct water.

RHBDF2 mutations are associated with tylosis, a familial esophageal cancer syndrome.

Tylosis esophageal cancer (TOC) is an autosomal-dominant syndrome characterized by palmoplantar keratoderma, oral precursor lesions, and a high lifetime risk of esophageal cancer. We have previously localized the TOC locus to a small genomic interval within chromosomal region 17q25. Using a targeted capture array and next-generation sequencing, we have now identified missense mutations (c.557T>C [p.Ile186Thr] and c.566C>T [p.Pro189Leu] in RHBDF2, which encodes the inactive rhomboid protease RHBDF2 (also known as iRhom2), as the underlying cause of TOC. We show that the distribution of RHBDF2 in tylotic skin is altered in comparison with that in normal skin, and immortalized tylotic keratinocytes have decreased levels of total epidermal growth factor receptor (EGFR) and display an increased proliferative and migratory potential relative to normal cells, even when normal cells are stimulated with exogenous epidermal growth factor. It would thus appear that EGFR signaling is dysregulated in tylotic cells. Furthermore, we also show an altered localization of RHBDF2 in both tylotic and sporadic squamous esophageal tumors. The elucidation of a role of RHBDF2 in growth-factor signaling in esophageal cancer will help to determine whether targeting this pathway in chemotherapy for this and other squamous cell carcinomas will be effective.

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

UNLABELLED: Pachyonychia congenita (PC), a rare autosomal dominant disorder characterized by hypertrophic nail dystrophy, is classified into two main clinical subtypes: PC-1 and PC-2. PC-1 is associated with mutations in the KRT6A or KRT16 genes, whereas PC-2 is linked to KRT6B or KRT17 mutations. Blood samples were collected from three generations of a new Chinese PC-1 family, including three PC patients and five unaffected family members. A novel missense mutation p.Leu128Pro (c.383T>C) was identified in a highly conserved helix motif in domain 1A of K16. The disease haplotype carried the mutation and cosegregated with the affection status. PolyPhen2 and SIFTS analysis rated the substitution as probably damaging; Swiss-Model analysis indicated that the structure of the mutant protein contained an unnormal α-helix. Overexpression of mutant protein in cultured cells led to abnormal cell morphology. CONCLUSION: The wider spectrum of KRT16 mutations suggests that changes in codons 125, 127, and 132 are most commonly responsible for PC-1 and that proline substitution mutations at codons 127 or 128 may produce more severe disease. This study extends the KRT16 mutation spectrum and adds new information on the clinical and genetic diversity of PC.

[Clinical and genetic characteristics of Buschke-Fischer-Brauer's disease in a Tunisian family]. / Etude clinique et génétique de la kératodermie palmoplantaire de Buschke-Fischer-Brauer dans une famille tunisienne.

BACKGROUND: Punctate palmoplantar keratoderma (PPPK), or Buschke-Fischer-Brauer's disease, is a rare form of genodermatosis with autosomal dominant transmission and with variable penetrance. Its molecular basis remains unknown. Two loci were found to be linked to this disease: one on 15q22 and the other on 8q24. We report the clinical and genetic characteristics of PPPK in a Tunisian family. PATIENTS AND METHODS: A Tunisian family with PPPK was identified through a proband. As far as possible, history taking, physical examination, histopathological tests and blood sampling for DNA extraction were carried out for each patient. RESULTS: Seventeen patients were included in this study. Age ranged from 15 to 81 years with a sex-ratio of 3.2 m/f. Lesions appeared between the ages of 10 and 65 years and at a mean of 28 years. Clinically, lesions ranged from few keratotic papules on the palms to coalescence of lesions in plaques over palmar and/or plantar surfaces. Hyperhydrosis, hypopigmented macules and nail dystrophy were frequently associated. In all patients, histopathological examination revealed thickening of the epidermis with compact orthohyperkeratosis overlying a small and sharply demarcated area of depressed epidermis. Mechanical measures and keratolytic ointments proved non-beneficial. Genotyping for chromosomes 8 and 15 as well as LOD scores confirmed genetic linkage with the suspected locus on chromosome 15q, with the interval of the locus in question reduced to 3.26 Mb. This region is flanked by markers D15S987 and D15S153. CONCLUSION: Our study of this family confirmed the classical characteristics of KPP-BFB as well as demonstrating several associated clinical signs of which the significance will be determined in subsequent studies. Further screening studies to identify mutated genes in the region of interest will help us to understand the molecular basis of this disease and hopefully to propose suitable treatment.

Mutation L437P in the 2B domain of keratin 1 causes diffuse palmoplantar keratoderma in a Chinese pedigree.

Diffuse palmoplantar keratoderma (DPPK) is an autosomal dominant genodermatosis characterized by uniform hyperkeratosis of the palm and sole epidermis. This disorder can be caused by mutations in the genes keratin 1, keratin 9, keratin 16, desmoglein 1 and plakoglobin. Here we present a DPPK Chinese pedigree and identify the aetiology as a novel missense mutation, L437P, located in a highly conserved helix motif in domain 2B of KRT1. Functional analysis shows that overexpression of the L437P mutant in cultured cells leads to abnormal intermediate filament networks and filament aggregation. This gain-of-function mutation highlights the role of domain 2B in mediating filament assembly.

Frontiers in keratodermas: pushing the envelope.

A clinically and genetically heterogeneous group of disorders, known collectively as the palmoplantar keratodermas, are unified by the phenotypic characteristic of a thickening of the skin over the palms and soles. Although spectacular progress has been made in understanding the basis of many genodermatoses, the genetic defects causing many of the keratodermas are still largely unknown. These unusual phenotypes are beginning to capture the attention of investigators in epidermal biology, and several compelling lines of evidence point to the cornified cell envelope and structural components of the desmosome as potential underlying targets of disease. It is anticipated that understanding the molecular basis of the keratodermas will underscore the importance of the integrity of the cell envelope and the desmosome, and provide new insights into the mechanisms of epidermal differentiation and related disorders.

[Pathological features and gene mutation analysis in two pedigrees of diffuse palmoplantar keratoderma].

We report the clinical and pathological features of two pedigrees of palmoplantar keratoderma (PPK), the expression of keratin 9 (K9) in palm tissue and the mutation of the keratin 9 gene (KRT9). Histopathology and immunohistochemical assessment was performed to analyze the epidermis in the palm of the probands. Genomic DNA of 46 family individuals was used for amplification of exon 1 of KRT9. The mutations were determined by direct sequencing. Epidermal abnormalities in the palm of the two probands were characterized by vacuolar changes of suprabasal keratinocytes accompanied by thickening of the living epidermis and stratum corneum. K9 was also expressed in particular epithelial tissues. Direct sequencing of polymerase chain reaction products revealed heterozygous missense mutations in exon 1 of KRT9 (N160S and L167S) in the two families, respectively. N160S and L167S of KRT9 are disease-causing mutations in these two Chinese pedigrees with epidermolytic palmoplanter keratoderma (EPPK).

Tissue-specific role of RHBDF2 in cutaneous wound healing and hyperproliferative skin disease.

OBJECTIVE: Gain-of-function (GOF) mutations in RHBDF2 cause tylosis. Patients present with hyperproliferative skin, and keratinocytes from tylosis patients' skin show an enhanced wound-healing phenotype. The curly bare mouse model of tylosis, carrying a GOF mutation in the Rhbdf2 gene (Rhbdf2 cub ), presents with epidermal hyperplasia and shows accelerated cutaneous wound-healing phenotype through enhanced secretion of the epidermal growth factor receptor family ligand amphiregulin. Despite these advances in our understanding of tylosis, key questions remain. For instance, it is not known whether the disease is skin-specific, whether the immune system or the surrounding microenvironment plays a role, and whether mouse genetic background influences the hyperproliferative-skin and wound-healing phenotypes observed in Rhbdf2 cub mice. RESULTS: We performed bone marrow transfers and reciprocal skin transplants and found that bone marrow transfer from C57BL/6 (B6)-Rhbdf2 cub/cub donor mice to B6 wildtype recipient mice failed to transfer the hyperproliferative-skin and wound-healing phenotypes in B6 mice. Furthermore, skin grafts from B6 mice to the dorsal skin of B6-Rhbdf2 cub/cub mice maintained the phenotype of the donor mice. To test the influence of mouse genetic background, we backcrossed Rhbdf2 cub onto the MRL/MpJ strain and found that the hyperproliferative-skin and wound-healing phenotypes caused by the Rhbdf2 cub mutation persisted on the MRL/MpJ strain.

A novel mutation and large size polymorphism affecting the V2 domain of keratin 1 in an African-American family with severe, diffuse palmoplantar keratoderma of the ichthyosis hystrix Curth-Macklin type.

Keratin gene mutations affecting nonhelical head and tail domains are not usually associated with prominent skin blistering and keratin filament clumping. Instead, they have been associated with several distinct clinical phenotypes, such as epidermolysis bullosa simplex with mottled pigmentation (mutation P25L in the V1 domain of keratin 5), epidermolysis bullosa simplex with migratory circinate erythema (frameshift mutation c1649delG in the V2 domain of keratin 5), striate palmoplantar keratoderma (PPK), and ichthyosis hystrix Curth-Macklin (different frameshift mutations in the V2 domain of keratin 1 (K1)). We have studied a family with severe, diffuse, nonepidermolytic PPK and verrucous hyperkeratotic plaques over the joints and in flexures and identified a new KRT1 gene mutation that is predicted to completely alter the K1 tail domain. In addition, a new K1 size polymorphism has been detected, which is especially prevalent among the African-American population. These results further emphasize the functional importance of the nonhelical tail domain in keratin molecules despite the obvious variability in the number of glycine loop motifs and underscore the broad phenotypic spectrum of disorders due to dominant keratin tail mutations.

Hereditary diffuse palmoplantar keratodermas in Slovenia: epidemiologic foci in remote rural areas.

BACKGROUND: Previous studies carried out in Slovenia revealed a high frequency of cases of hereditary diffuse palmoplantar keratodermas (DPPK). The relatively small total population of about two million in a small territory and an efficient public health service were favorable preconditions for such a study. METHODS: Existing hospital and outpatient department records served as starting points. Patients were invited to come for a follow-up examination, and visiting the patients at their homes enabled us to gather further data. Thus efforts were made to include all patients with hereditary DPPK in Slovenia. RESULTS: Altogether 170 DPPK patients were detected, giving a prevalence of 8.3 per 100,000 inhabitants. The patients originated from remote, mostly mountainous districts, where the local DPPK prevalence highly significantly exceeded the average Slovene prevalence. The segregation ratio showed an autosomal dominant mode of inheritance. The percentage of persons affected was 34.4% (95% confidence interval 29.8-39.4), lower than expected for autosomal dominant inheritance (the difference is highly significant, P < 0.00001; exact binomial test). CONCLUSION: One autosomal dominant gene alone does not fully explain the transmission of the disorder to siblings. Evidence is produced that additional factors are necessary for the transmission of this genetic condition. The degree of consanguinity and the physical pressure on palms and soles seem to play an important part. It is reasonable to expect that molecular-biology studies linked to the epidemiological data could contribute to the solution of the problem.