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Notes: Plectin is a 500kDa protein involved in cytoskeleton-plasma membrane attachment with a wide tissue distribution including cutaneous and airway epithelia, muscle and neuronal tissue. Recently, mutations in the gene encoding plectin (PLECI) have been implicated in the pathogenesis of an autosomal recessive variant of epidermolysis bullosa simplex in which cutaneous blistering starting in the neonatal period is associated with muscular dystrophy in later life. In this study, we report two unrelated patients, both of consanguineous parentage, who presented with cutaneous blistering and a hoarse cry from birth. Both experienced inspiratory stridor and respiratory distress, necessitating emergency tracheostomy in one case. Immunoreactivity to monoclonal antibodies against plectin was absent or markedly reduced in skin biopsies from both patients. Electron microscopy revealed a low intraepidermal plane of cleavage and hypoplastic hemidesmosomes with a reduced association with keratin intermediate filaments. Direct sequencing of PLEC1 in each case demonstrated two novel homozygous frameshift deletion mutations. 5069del19 and 5905del2, which both create downstream premature termination codons. Although currently neither patient has symptoms of muscle disease, the identification of mutations in PLEC1 may be predictive for the future development of muscular dystrophy. Recessive epidermolysis bullosa simplex resulting form abnormalities in plectin should be considered in the differential diagnosis of cutaneous blistering, hoarseness and stridor in infancy.

Notes: Background Keratins are a multigene family of intermediate filament proteins that are differentially expressed in specific epithelial tissues. To date, no type II keratins specific for the inner root sheath of the human hair follicle have been identified. Objectives To characterize a novel type II keratin in mice and humans. Methods Gene sequences were aligned and compared by BLAST analysis. Genomic DNA and mRNA sequences were amplified by polymerase chain reaction (PCR) and confirmed by direct sequencing. Gene expression was analysed by reverse transcription (RT)–PCR in mouse and human tissues. A rabbit polyclonal antiserum was raised against a C-terminal peptide derived from the mouse K6irs protein. Protein expression in murine tissues was examined by immunoblotting and immunofluorescence. Results Analysis of human expressed sequence tag (EST) data generated by the Human Genome Project revealed a fragment of a novel cytokeratin mRNA with characteristic amino acid substitutions in the 2B domain. No further human ESTs were found in the database; however, the complete human gene was identified in the draft genome sequence and several mouse ESTs were identified, allowing assembly of the murine mRNA. Both species' mRNA sequences and the human gene were confirmed experimentally by PCR and direct sequencing. The human gene spans more than 16 kb of genomic DNA and is located in the type II keratin cluster on chromosome 12q. A comprehensive immunohistochemical survey of expression in the adult mouse by immunofluorescence revealed that this novel keratin is expressed only in the inner root sheath of the hair follicle. Immunoblotting of murine epidermal keratin extracts revealed that this protein is specific to the anagen phase of the hair cycle, as one would expect of an inner root sheath marker. In humans, expression of this keratin was confirmed by RT–PCR using mRNA derived from plucked anagen hairs and epidermal biopsy material. By this means, strong expression was detected in human hair follicles from scalp and eyebrow. Expression was also readily detected in human palmoplantar epidermis; however, no expression was detected in face skin despite the presence of fine hairs histologically. Conclusions This new keratin, designated K6irs, is a valuable histological marker for the inner root sheath of hair follicles in mice and humans. In addition, this keratin represents a new candidate gene for inherited structural hair defects such as loose anagen syndrome.

Notes: Pachyonychia congenita (PC) is a group of inherited ectodermal dysplasias, the characteristic phenotype being hypertrophic nail dystrophy. Two main clinical subtypes, PC-1 and PC-2, are inherited as autosomal dominant disorders, but other less well characterized clinical forms also exist. The PC-1 phenotype may be distinguished by the absence of the epidermal cysts found in PC-2, and it has been shown to be caused by mutations in either keratin K16 or its expression partner, the K6a isoform of K6. Mutations in K16 have also been shown to cause a milder related phenotype, focal non-epidermolytic palmoplantar keratoderma. Recently, we have developed a long-range polymerase chain reaction (PCR) strategy which allows specific amplification of the entire functional K16 gene (KRT16A), without amplification of the two K16 pseudogenes (ψKRT16B and ψKRT16C), enabling mutation analysis based on genomic DNA. Here, using this methodology, we describe novel mutations R127P and Q122P in the helix 1A domain of K16 in two families presenting with PC-1. Both mutations were excluded from 50 normal unrelated individuals by restriction enzyme analysis of K16 PCR fragments. In one family, ultrastructural analysis was performed, revealing distinctive tonofilament abnormalities. Specifically, keratin filament bundles were greatly condensed, but did not form the dense amorphous aggregates seen in a number of other keratin disorders. In the second kindred, autosomal dominant cataract was present in some but not all members affected by PC. As the cataract phenotype did not fully cosegregate with the K16 mutation, and given that K16 is not expressed in the lens, these two phenotypes may be coincidental.

Notes: A young girl with clinical features of pachyonychia congenita type 1 was unusual in that the typical skin and nail changes were not noted until the age of 6 years. Direct sequencing of the KRT16A gene, encoding keratin K16, revealed a novel mutation K354N in the central 2B domain of the K16 polypeptide. The mutation created a new BsmI restriction site and therefore, the mutation was confirmed in the patient and excluded from both parents and 50 normal, unrelated individuals by BsmI digestion of KRT16A polymerase chain reaction products. This is the first time a mutation has been described in this location in a keratin other than K14, where similar mutations cause the milder Weber–Cockayne and/or Köbner types of epidermolysis bullosa simplex.

Notes: [Auszug] We have identified mutations in keratins K5 (Arg331Cys) and K14 (Val270Met) in two kinships affected by the dominantly–inherited skin blistering disease, Weber–Cockayne epidermolysis bullosa simplex (EBS–WC). Linkage analysis, DNA sequencing and clinical and ultrastructural ...

Notes: [Auszug] We report that mutation in the gene for plectin, a cytoskeleton–membrane anchorage protein, is a cause of autosomal recessive muscular dystrophy associated with skin blistering (epidermolysis bullosa simplex). The evidence comes from absence of plectin by antibody staining in affected ...