1/14. A premature stop codon mutation in the 2B helix termination peptide of keratin 5 in a German epidermolysis bullosa simplex Dowling-Meara case.epidermolysis bullosa simplex (EBS) is caused by defective assembly of keratin intermediate filaments in basal keratinocytes and recent studies indicated causal mutations in the keratin KRT5 and KRT14 genes. In this study, we describe a novel KRT5 mutation in a German sporadic case of EBS Dowling-Meara. Transition of G to T (nucleotide position 2334) leads to a premature stop codon (E477stop, residue 93 of the 2B helix) in the last residue of the highly conserved helix-termination peptide K/LLEGE of the 2B rod domain of keratin K5. This represents the first premature stop codon mutation identified within the K/LLEGE motif of any disorder reported so far that is caused by keratin mutations.- - - - - - - - - - ranking = 1keywords = intermediate (Clic here for more details about this article) |
2/14. Myopathy, myasthenic syndrome, and epidermolysis bullosa simplex due to plectin deficiency.plectin, an intermediate filament linking protein, is normally associated with the sarcolemma, nuclear membrane, and intermyofibrillar network in muscle, and with hemisdesmosomes in skin. A 20-year-old female with epidermolysis bullosa simplex since birth had progressive ocular, facial, limb, and trunkal weakness and fatigability since age 9, fivefold CK elevation, a 25% decrement with myopathic motor unit potentials and increased electrical irritability on electromyography, and no anti-acetylcholine receptor (AChR) antibodies. plectin expression was absent in muscle and severe plectin deficiency was noted in skin. Morphologic studies revealed necrotic and regenerating fibers and a wide spectrum of ultrastructural abnormalities: large accumulations of heterochromatic and lobulated nuclei, rare apoptotic nuclei, numerous cytoplasmic and few intranuclear nemaline rods, disarrayed myofibrils, thick-filament loss, vacuolar change, and pathologic alterations in membranous organelles. Many endplates (EPs) had an abnormal configuration with chains of small regions over the fiber surface and a few displayed focal degeneration of the junctional folds. The EP AChR content was normal. in vitro electrophysiologic studies showed normal quantal release by nerve impulse, small miniature EP potentials, and fetal as well as adult AChR channels at the EP. Our findings support the notion that plectin is essential for the structural integrity of muscle and skin, and for normal neuromuscular transmission.- - - - - - - - - - ranking = 1keywords = intermediate (Clic here for more details about this article) |
3/14. A keratin 14 'knockout' mutation in recessive epidermolysis bullosa simplex resulting in less severe disease.epidermolysis bullosa simplex (EBS) is a blistering skin disease caused in most cases by mis-sense mutations in genes encoding the basal epidermal keratin (K) 5 and K14. The inheritance is usually autosomal dominant and the mutant keratin proteins appear to exert a dominant negative effect on the keratin intermediate filament cytoskeleton in basal keratinocytes. We report a child with a homozygous K14 mutation resulting in the complete absence of K14 protein in the epidermis; remarkably, he only had mild to moderate disease. Electron microscopy of a skin biopsy showed a marked reduction in numbers of keratin intermediate filaments in the basal keratinocytes. Immunofluorescence microscopy using monoclonal antibody LL001 against K14 showed no staining, suggesting a functional knockout of K14. sequence analysis of genomic dna revealed a homozygous mutation in codon 31 of K14 that resulted in a premature stop codon further downstream in exon 1. The child's mother, who is unaffected by the disease, is heterozygous for the mutation. The consanguineous father was unaffected and unavailable for testing. The resulting mRNA is predicted to encode a protein of 116 amino acids, of which the first 30 are identical to the normal K14 sequence, and the remaining 86 residues are mis-sense sequence. Four previously reported cases of autosomal recessive EBS with functional knockout of K14 were severely affected by blistering, in contrast to our patient in whom the predicted protein has only the first 30 amino acids of K14 and is therefore the closest to a true knockout of K14 protein yet identified.- - - - - - - - - - ranking = 2keywords = intermediate (Clic here for more details about this article) |
4/14. Deletion of the cytoplasmatic domain of BP180/collagen XVII causes a phenotype with predominant features of epidermolysis bullosa simplex.BP180/collagen XVII is a hemidesmosomal transmembrane molecule serving as cell-surface receptor. Mutations in its gene cause junctional epidermolysis bullosa. Here, we report a patient with mutations in the gene for BP180/collagen XVII, COL17A1, but predominant phenotypic features of epidermolysis bullosa simplex. At birth, the proband presented with bullous lesions on the trunk, face, and hands. Ultrastructurally, hemidesmosomes were fairly normal, but the attachment of intermediate filaments with the hemidesmosomal plaques appeared to be impaired. blister formation demonstrated both intraepidermal and junctional cleavage. Immunofluorescence staining with antibodies to keratins, several hemidesmosomal proteins, and the extracellular domain of BP180/collagen XVII showed normal staining patterns, whereas an antibody against the intracellular domain of BP180/collagen XVII yielded a negative immunofluorescence signal. Analysis of BP180/collagen XVII cDNA revealed a 1172 bp deletion corresponding to an in-frame deletion from Ile-18 to Asn-407 from the intracellular domain of the polypeptide. mutation analysis of the COL17A1 gene disclosed a paternal nonsense mutation, R1226X, and a large maternal genomic deletion extending from intron 2 to intron 15, but no mutations in basal keratin genes. These findings underline the functional importance of the intracellular BP180/collagen XVII domain for the interaction of hemidesmosomes with keratin intermediate filaments and for the spatial stability of basal keratinocytes, and provide a functional explanation for the epidermolysis-bullosa- simplex-like phenotype. Further, the data demonstrate that defects in a given gene can cause unexpected phenotypes of epidermolysis bullosa categories, depending on the function of the affected protein domain.- - - - - - - - - - ranking = 2keywords = intermediate (Clic here for more details about this article) |
5/14. Partial revertant mosaicism of keratin 14 in a patient with recessive epidermolysis bullosa simplex.A patient with recessive epidermolysis bullosa simplex due to a previously described homozygous KRT14 1842-2A-->C splice-site mutation was re-examined, because we unexpectedly found signs of revertant mosaicism. The germline mutation resulted in different aberrant transcripts containing premature termination codons, all leading to truncated keratin 14 proteins. Basal keratinocytes in skin and in culture completely lacked keratin 14 and intermediate filaments. From this keratin 14-/- patient we started cultures from a new skin biopsy and here, we serendipitously found keratinocytes that spontaneously expressed keratin 14. This biopsy had been taken from an area of skin that was clinically affected, because blisters could simply be evoked by gentle rubbing. Immunofluorescence and electron microscopy of additional biopsies from this skin area revealed a mosaic expression of keratin 14 and reappearance of intermediate filaments in basal keratinocytes. immunoblotting showed a revertant keratin 14 polypeptide with seemingly normal molecular weight. dna analysis of exon 2 and its flanking intron borders showed no additional mutations in the genomic KRT14 sequence. Analysis of mRNA isolated from mosaic skin keratinocytes revealed an additional in-frame transcript (1844T-->G, 1845Delta6) that codes for an abnormal keratin 14 polypeptide with a two residue deletion and one amino acid change. The re-expression of a revertant, albeit abnormal, keratin 14 polypeptide, so-called partial revertant mosaicism, accounts for the antibody staining pattern and for the reappearance of intermediate filaments, which however, are semifunctional and not able to revert the clinical phenotype. The combination of a keratin 14-positive and a keratin 14-negative cell population in epidermis as well as in cultured keratinocytes suggests that the cellular reversion might be caused by an endogenous factor. We hypothesize that a second somatic modulating factor in the genome that affects the processing of the mutant KRT14 pre-mRNA may underlie this phenomenon.- - - - - - - - - - ranking = 3keywords = intermediate (Clic here for more details about this article) |
6/14. Deletion of a cytoplasmic domain of integrin beta4 causes epidermolysis bullosa simplex.integrin alpha6beta4 is a hemidesmosomal transmembrane molecule involved in maintaining basal cell-matrix adhesion through interaction of the large intracytoplasmic tail of the beta4 subunit with the keratin intermediate filament network, at least in part through its binding with plectin and BP180/type XVII collagen. Here we report a patient with predominant features of epidermolysis bullosa simplex due to a mutation in the integrin beta4 gene. The patient, a 49-y-old female, had mild blistering of hands and feet from birth on, dystrophy of the nails with onychogryposis, and enamel hypoplasia. She had no alopecia and no history of pyloric atresia. Electron microscopy and antigen mapping of a skin blister revealed that the level of separation was intraepidermal, low in the basal keratinocytes through the attachment plaque of the hemidesmosome. Immuno-fluorescence microscopy revealed absent binding of monoclonal antibody 450-11 A against the third fibronectin III repeat on the intracellular domain of integrin beta4, whereas binding was reduced with monoclonal antibodies recognizing epitopes on amino-terminal and carboxy-terminal ends of the polypeptide. At the molecular level the phenotype was caused by a novel 2 bp deletion 4733delCT in ITGB4, resulting in in-frame skipping of exon 36 and a deduced 50 amino acid deletion (1450-1499) within the third fibronectin type III repeat in the cytoplasmic domain of the integrin beta4 polypeptide. Immunoblot analysis demonstrated a 5 kDa shorter beta4 polypeptide. The 4733delCT mutation was heterozygously present in the dna. The patient is also expected to be heterozygous for a null allele, as no full-size protein was detected in vitro and the epitope 450-11 A was absent in vivo. These data show that deletion of the third fibronectin type III repeat in the cytoplasmic domain of integrin beta4, which is thought to interact with BP180/type XVII collagen, is clinically pathogenic and results in a mild phenotype with predominant features of epidermolysis bullosa simplex.- - - - - - - - - - ranking = 1keywords = intermediate (Clic here for more details about this article) |
7/14. A usual frameshift and delayed termination codon mutation in keratin 5 causes a novel type of epidermolysis bullosa simplex with migratory circinate erythema.We report here two unrelated families in japan and korea having patients with a unique type of epidermolysis bullosa simplex and a novel mutation in the keratin gene KRT5, i.e., a frameshift and delayed stop codon inconsistent with any subtype described before. The patients showed migratory circinate erythema and multiple vesicles on the circular belt-like areas affected by erythema. Electron microscopy of skin biopsies showed a reduction in the number of keratin intermediate filaments in the basal cells without tonofilament clumping. We identified a novel heterozygous deletion mutation (1649delG of KRT5) in both cases. This deletion is predicted to produce a mutant keratin 5 protein with a frameshift of its terminal 41 amino acids and 35 amino acids longer than the wild-type keratin 5 protein due to a delayed termination codon. As the same abnormal elongated mutant KRT5 gene was found in the independent families, the predicted abnormal elongated keratin protein is likely to lead to an atypical clinical phenotype that has never been reported, possibly by interfering with the functional interaction between keratin and its associated proteins.- - - - - - - - - - ranking = 1keywords = intermediate (Clic here for more details about this article) |
8/14. Novel keratin 14 gene mutations in patients from hungary with epidermolysis bullosa simplex.Mutations in genes keratin 5 (KRT5) and 14 (KRT14) encoding the basal type keratin intermediate filaments have been identified in epidermolysis bullosa simplex (EBS) families and are likely to cause skin fragility. Three novel keratin 14 mutations in cases from the Hungarian Epidermolysis Bullosa Centre are reported. In a 7-year-old boy with Dowling-Meara type EBS (DM-EBS), who had severe skin symptoms with extended herpetiform blisters, a novel amino acid substitution N123K in keratin 14 had been detected. A 26-year-old woman with mild DM-EBS with prominent palmoplantar hyperkeratosis and without active blister formation had a novel R125G mutation in keratin 14. In a 6-year-old girl, with Weber-Cockayne type EBS (WC-EBS) with palmoplantar blisters and moderate mental retardation, a novel V133L substitution was detected. Her pedigree showed autosomal dominant mode of inheritance; in the two other families, only the index patients were affected. The N123K and R125G mutations causing DM-EBS phenotypes are located within the helix initiation motif of the rod domain, whereas the very close V133L mutation underlying the WC-EBS phenotype is outside of this region. These novel amino acid substitutions provide further information for genotype-phenotype correlation in KRT14 mutations, and demonstrate the first molecular genetic data in EBS patients from hungary.- - - - - - - - - - ranking = 1keywords = intermediate (Clic here for more details about this article) |
9/14. A new mutation in the linker 12 domain of keratin 5 in a Chinese family with Weber-Cockayne epidermolysis bullosa simplex.A previously undescribed missense mutation was detected in the L12 domain of keratin 5 (K5) in a Chinese family with Weber-Cockayne epidermolysis bullosa simplex. Direct sequencing of the PCR products identified a single base substitution (983A-->G) that changes the aspartic acid residue at codon 328 to glycine in all affected family members, while no mutation was observed either in the healthy individual or 50 unrelated control samples. Asp328 of K5 is remarkably conserved among all type II keratins. D328G is the fourth mutation found to affect this residue in K5-related epidermolysis bullosa simplex, indicating the importance of Asp328 for K5 structure and the dramatic effect that fine changes can have on keratin intermediate filament integrity.- - - - - - - - - - ranking = 1keywords = intermediate (Clic here for more details about this article) |
10/14. A functional "knockout" of human keratin 14.The importance of keratins and other intermediate filaments in the maintenance of tissue structure is emphasized by the discovery that many hereditary skin-blistering diseases are caused by mutations in keratin genes. Here, we describe a situation in which keratin 14 (K14) is missing altogether in the epidermis: A homozygous 2-nucleotide deletion in exon I of the K14 gene causes premature termination of the mRNA transcripts upstream from the start of the rod domain and results in a K14 null phenotype. In this individual no keratin intermediate filaments are visible in basal epidermal cells, although filaments are present in the upper layers of the epidermis. No compensating keratin expression is detected in vivo, and K14 mRNA is down-regulated. The individual, diagnosed as Kobner (generalized) EBS, suffers from severe widespread keratinocyte fragility and blistering at many body sites, but although the phenotype is severe, it is not lethal. This K14-/- phenotype confirms that only one K14 gene is expressed in human epidermis and provides an important model system for examining the interdependence of different keratin filament systems and their associated structures in the skin.- - - - - - - - - - ranking = 2keywords = intermediate (Clic here for more details about this article) |
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