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Epidermolytic palmoplantar keratoderma due to a novel type of keratin mutation, a 3‐bp insertion in the keratin 9 helix termination motif
Author(s) -
C. M. Coleman,
Colin S. Munro,
Fjd Smith,
Jouni Uitto,
W.H. Irwin McLean
Publication year - 1999
Publication title -
british journal of dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.304
H-Index - 179
eISSN - 1365-2133
pISSN - 0007-0963
DOI - 10.1046/j.1365-2133.1999.02715.x
Subject(s) - keratin 6a , genodermatosis , palmoplantar keratoderma , biology , keratin , epidermolysis bullosa simplex , missense mutation , epidermolytic hyperkeratosis , genetics , exon , mutation , microbiology and biotechnology , intermediate filament , hyperkeratosis , gene , cytoskeleton , cell
Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant genodermatosis characterized by diffuse keratoderma, typically with an erythematous border. Histologically, palmoplantar epidermis shows suprabasal cytolysis and ultrastructurally, tonofilament aggregation with overlying epidermolytic hyperkeratosis. Mutations in the KRT9 gene, encoding keratin 9 (K9), a cytoskeletal protein expressed exclusively in suprabasal keratinocytes of palmoplantar epidermis, have been reported to cause EPPK. To date, all KRT9 defects reported in EPPK have been missense mutations in exon 1, which encodes the start of the α‐helical rod domain. However, based on studies of other keratin disorders, it was postulated that mutations at the other end of the rod domain might also produce the EPPK phenotype. Here, we report the first mutation in the 2B domain of KRT9, 1362ins3, leading to an insertion of histidine in the helix termination motif of the K9 polypeptide. Insertional mutations have not been previously described in keratins. The phenotype of this case is similar to EPPK caused by 1A domain mutations, demonstrating that mutations in either of the helix boundary motif sequences of K9 are detrimental to keratin function and keratinocyte structure.