A 64-year-old man presented with focal hyperkeratotic plaques on the fingers, palms, and soles. Histopathologic and electron microscopic results were consistent with striate palmoplantar keratoderma. Treatment with topical keratolytics was unsuccessful. Striate palmoplantar keratoderma or Brunauer-Fohs-Siemens syndrome is an autosomal dominant condition that presents with linear hyperkeratosis on the palms and fingers and focal plaques on the plantar aspects of the feet. Histopathologic features include hyperkeratosis, hypergranulosis, and acanthosis with no epidermolysis. Electron microscopic examination shows diminished desmosomes, clumped keratin filaments, and enlarged keratohyalin granules. The syndrome has been linked to mutations in desmoglein 1, desmoplakin, and keratin 1. Treatment may include keratolytics, oral retinoids, and surgical debridement.
"Congenitally, palmar plantar hyperkeratosis can also be caused by mutations in the genes which code for epidermal proteins. Mutant keratin 1, keratin 10 , Cx26 (Vohwinkel's syndrome)  and desmosomal proteins  have all been reported to be genetically linked to palmar plantar hyperkeratosis. In the case of Cx43 mutations, it is currently not known whether the mechanism by which Cx43 mutants cause palmar plantar hyperkeratosis is somehow associated to these other skin disease-linked proteins. "
[Show abstract][Hide abstract] ABSTRACT: Although there are currently 62 mutants of Cx43 (connexin43) that can cause ODDD (oculodentodigital dysplasia), only two mutants have also been reported to cause palmar plantar hyperkeratosis. To determine how mutants of Cx43 can lead to this skin disease, REKs (rat epidermal keratinocytes) were engineered to express an ODDD-associated Cx43 mutant always linked to skin disease (fs260), an ODDD-linked Cx43 mutant which has been reported to sometimes cause skin disease (fs230), Cx43 mutants which cause ODDD only (G21R, G138R), a mouse Cx43 mutant linked to ODDD (G60S), a non-disease-linked truncated Cx43 mutant that is trapped in the endoplasmic reticulum (Delta244*) or full-length Cx43. When grown in organotypic cultures, of all the mutants investigated, only the fs260-expressing REKs consistently developed a thinner stratum corneum and expressed lower levels of Cx43, Cx26 and loricrin in comparison with REKs overexpressing wild-type Cx43. REKs expressing the fs260 mutant also developed a larger organotypic vital layer after acetone-induced injury and exhibited characteristics of parakeratosis. Collectively, our results suggest that the increased skin disease burden exhibited in ODDD patients harbouring the fs260 mutant is probably due to multiple additive effects cause by the mutant during epidermal differentiation.
[Show abstract][Hide abstract] ABSTRACT: Inherited keratinizing disorders are caused by mutations in the genes encoding cornified cell envelope proteins, enzymes and their inhibitors, adhesion molecules, cytoskeletal proteins and others in the epidermis. These molecules are known to regulate differentiation, proliferation and cell adhesions. Intriguingly, some keratinizing disorders show blistering skin lesions, while some inherited blistering disorders show abnormal keratinization. Therefore, hereditary keratinizing and blistering diseases are closely related and show overlapping genetic backgrounds. In this review, we overviewed keratinizing and blistering disorders in terms of overlapping of the two disease groups. Gene mutations in desmosomal components cause striate keratoderma, Naxos disease, epidermolytic palmoplantar keratoderma and plakophilin deficiency, which first show skin fragility and blisters and later hyperkeratosis. Gene mutations in hemidesmosomal components cause various forms of epidermolysis bullosa, some of which show hyperkeratosis on the nails, palms and soles, in addition to blister formation. Diseases with gene mutations in calcium pump proteins are Darier disease and Hailey-Hailey disease, which show clinicopathological overlaps and develop both keratinizing and blistering skin lesions. Finally, gene mutations in epidermal keratins cause epidermolysis bullosa simplex, epidermolytic ichthyosis, superficial epidermolytic ichthyosis, epidermolytic palmoplantar keratoderma and pachyonychia congenita/focal palmoplantar keratoderma, which show thickening of the palms and soles with underlying blister formation. In general, responsible proteins for diseases developing both keratinizing and blistering conditions are adhesion molecules, calcium pump proteins and keratins, but not connexins, cornified cell envelop proteins, enzymes or inhibitors. It is still unknown how particular keratinizing diseases develop blisters and vice versa.
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