Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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Epidermolytic hyperkeratosis (EHK), (bullous congenital ichthyosiform erythroderma), is an autosomal dominant human skin disorder. Recently, we and others have described mutations in keratins 1 and 10 (K1 and K10) in patients with this disease. Structure-function models predict that these mutations would impair normal filament assembly and function. We have extended our earlier studies to include 8 more incidences of EHK. In half of these families, we were unable to locate a mutation within the rod domains of either K1 or K10. However, polymorphic restriction site and sequence analysis of the other families revealed a mutational hot spot within the 1A alpha-helical segment of K10. These involve Arginine to Histidine, Arginine to Cysteine and Arginine to Leucine substitutions at residue 10 of the rod domain. Interestingly, mutations in the corresponding Arginine residue in keratin K14 have been identified in patients with epidermolysis bullosa simplex. The large number of mutations found at this position in both keratins K10 and K14 suggests that other epithelia cell disorders will be discovered that are caused by the corresponding mutation in related type I keratin genes.
Hum Mol Genet 1993 Dec
PMID:A mutational hot spot in keratin 10 (KRT 10) in patients with epidermolytic hyperkeratosis. 750 30

The inherited mechanobullous disorder, junctional epidermolysis bullosa (JEB), is characterized by extensive blistering and erosions of the skin and mucous membranes. The diagnostic hallmarks of JEB include ultrastructural abnormalities in the hemidesmosomes of the cutaneous basement membrane zone, as well as an absence of staining with antibodies against the anchoring filament protein, laminin 5. Therefore, the three genes encoding alpha 3, beta 3 and gamma 2 chains of laminin 5, known as LAMA3, LAMB3 and LAMC2, are candidate genes for JEB. We have previously demonstrated mutations in the LAMB3 and LAMC2 genes in several families with JEB. We initiated mutation analysis from an affected child by PCR amplification of individual LAMA3 exons, followed by heteroduplex analysis. Nucleotide sequencing of heteroduplexes identified a homozygous nonsense mutation within domain I/II of the alpha 3 chain. These findings provide the first evidence that nonsense mutations within the LAMA3 gene are also involved in the pathogenesis of JEB, and indicate that mutations of all three genes of laminin 5 can result in the JEB phenotype.
Hum Mol Genet 1995 May
PMID:A homozygous nonsense mutation in the alpha 3 chain gene of laminin 5 (LAMA3) in lethal (Herlitz) junctional epidermolysis bullosa. 763 58

Junctional epidermolysis bullosa inversa is an autosomal recessive blistering skin disease with an ultrastructural hemidesmosome defect similar to that of the Herlitz disease, yet with a non-lethal and different course of the disease. Its delineation is based on five geographically associated Norwegian families where all parents are likely to carry a mutant EBR2A allele identical in descent. Three informative families show a lod score of +1.65 at zero recombination to a trinucleotide repeat marker in intron 20 of the laminin gamma 1 (LAMC1, previously LAMB2) locus on 1q31. The four patients of these families are all homozygous for the 146 bp LAMC1 allele present only on 5% of random Norwegian chromosomes. The daughter of a deceased patient in a fourth family carries the same 146 bp allele. This extreme association confirms that the disease locus, EBR2A, is at or closely linked to LAMC1. Localized and generalized Mitis types as well as the majority of tested families with the Herlitz type of junctional epidermolysis bullosa appeared not to be similarly linked or associated to LAMC1. The MspI and AluI RFLPs of LAMC1 showed absolute allelic association. Each of the two RFLP haplotypes showed association to either 'long' or 'short' intron 20 STR alleles.
Hum Mol Genet 1994 Aug
PMID:Junctional epidermolysis bullosa inversa (locus EBR2A) assigned to 1q31 by linkage and association to LAMC1. 798 20

The COL7A1 gene, which encodes type VII collagen, has been implicated as a candidate gene for dominantly and recessively inherited forms of dystrophic epidermolysis bullosa. In this study, hamster and human cDNA clones, which encode the previously uncharacterized carboxyl-terminal portion of type VII collagen, have been isolated and characterized. The previously uncharacterized carboxyl-terminal NC-2 non-collagenous domain is shown to be comprised of 161 amino acids in humans, 170 amino acids in hamster and to contain 8 conserved cysteines in each species. The 6 most carboxyl-terminal cysteines are contained in a conserved motif similar to domains found in Kunitz protease inhibitors, and most closely resembling a similar motif found in the carboxyl-terminal globular domain of the alpha 3 chain of type VI collagen. Also contained in the highly acidic NC-2 domain are a number of potential sites for phosphorylation by casein kinases. Human genomic clones containing 24 exons of COL7A1 were isolated and characterized. The NC-2 domain is encoded by 7 of these exons, which include a junctional exon encoding the end of the collagenous region and the beginning of the NC-2 domain and a final exon encoding the end of the NC-2 domain and 333 bp of 3' untranslated sequences. Comparison of hamster and human sequences shows the region surrounding the junction of the collagenous and NC-2 domains to be particularly conserved. This region is likely to contain residues involved in the proteolytic removal of the NC-2 domain and cysteines involved in formation of the disulfide linkages which stabilize type VII collagen dimers.
Hum Mol Genet 1993 Mar
PMID:The carboxyl-terminal half of type VII collagen, including the non-collagenous NC-2 domain and intron/exon organization of the corresponding region of the COL7A1 gene. 849 16

Pretibial epidermolysis bullosa (PEB) is a rare variant of dominant dystrophic EB (DDEB) in which recurrent blistering with scarring predominantly involves the pretibial skin. Although blistering appears to be localized clinically, electron microscopy of the dermalepidermal junction in patients with PEB reveals anchoring fibril abnormalities that are not restricted to the predilection sites. Furthermore, PEB cannot be distinguished from the generalized (Cockayne-Touraine and Pasini) types of DDEB on the basis of anchoring fibril morphology alone. The generalized forms of DDEB have been linked to the type VII collagen gene (COL7A1) on chromosome 3p21. In this study, we sought to test the hypothesis that mutations underlying PEB also reside in COL7A1. We initiated mutational analysis in COL7A1 in a large five-generation PEB family of Taiwanese descent. We identified a G-to-T transversion at nt position 7867, which results in a glycine-to-cysteine substitution (G2623C) in exon 105. This mutation was confirmed in affected family members using the loss of a SmaI restriction site, and when used for linkage analysis, together with an intragenic PvuII polymorphism and several flanking markers, resulted in a LOD score of Z = 3.61 at theta = 0 in this family. This is the first demonstration of genetic linkage and mutation analysis in PEB, and illustrates that the Cockayne-Touraine, Pasini, and now the pretibial clinical variants of DDEB are allelic, resulting from different glycine substitution mutations in the type VII collagen gene.
Hum Mol Genet 1995 Sep
PMID:Pretibial epidermolysis bullosa: genetic linkage to COL7A1 and identification of a glycine-to-cysteine substitution in the triple-helical domain of type VII collagen. 854 42

Keratins K6 and K16 are expressed in suprabasal interfollicular epidermis in wound healing and other pathological conditions associated with hyperproliferation, such as psoriasis and are induced when keratinocytes are cultured in vitro. However, these keratins are also constitutively expressed in normal suprabasal mucosal and palmoplantar keratinocytes. Mutations in keratins have been reported in the basal keratin pair K5 and K14 in epidermolysis bullosa simplex and in suprabasal epidermal keratins K1, K2 and K10 in epidermolytic ichthyoses. Two families with autosomal dominant disorder of focal non epidermolytic palmoplantar keratoderma, have oral mucosal and follicular lesions in addition to the palmoplantar hyperkeratosis. Previous studies have shown linkage in these families to the type I keratin gene cluster at 17q12-q21 and this report shows that the cDNA of affected members of both families have novel heterozygous mutations in the expressed keratin 16 gene. These mutations (R10C and N8S) lie in the helix initiation motif of the 1A domain. These mutations do not appear to cause epidermolysis on light or electron microscopy, which may reflect differences in function, assembly or interaction of the 'hyperproliferative' or 'mucoregenerative' keratins from other major types of keratins. The mutations reported here are the first to describe the molecular pathology of focal non epidermolytic palmoplantar keratoderma.
Hum Mol Genet 1995 Oct
PMID:Novel mutations in keratin 16 gene underly focal non-epidermolytic palmoplantar keratoderma (NEPPK) in two families. 859 10

In the past 5 years enormous progress have been made in our understanding of the molecular basis for a number of inherited skin diseases characterized by easy blistering of the skin and the mucous membranes after minor physical trauma. This increased fragility of the skin or its appendages is due to molecular defects in genes coding for different intra- and extracellular structural proteins which are responsible for mechanical strength at their sites of expression. These diseases encompass the group of epidermolysis bullosa and disorders of cornification such as bullous forms of ichthyosis, palmoplantar keratoderma, and pachyonychia congenita. On the basis of clinical, morphological, and ultrastructural observations the epidermolysis bullosa group has been divided into three major categories. In epidermolysis bullosa simplex blister formation appears within the basal cell layer of the epidermis, and many mutations have been found in the genes of keratin 5 and 14 which are both expressed in basal keratinocytes. Epidermolytic hyperkeratosis leads to an epidermal separation in the suprabasal cell layers. In these patients numerous point mutations have now been described in the suprabasally expressed genes of keratin 1 and 10. In ichthyosis bullosa of Siemens blisters occur in the more upper suprabasal epidermis coincidental with the expression of keratin 2e, and mutations have been detected in the corresponding gene. In epidermolytic palmoplantar hyperkeratosis the suprabasal epidermal splitting is restricted to palms and soles of the patient. In keratin 9, which reveals such an exclusive expression pattern, molecular defects have indeed been recognized. Most recently in two different clinical subtypes of pachyonychia congenita, which is characterized by defective nails and focal palmoplantar hyperkeratosis, point mutations have been found in the genes coding for keratins 6, 16, and 17. In junctional epidermolysis bullosa the separation takes place within the dermal-epidermal basement membrane at the level of the lamina lucida, and mutations have been found in three genes coding for different laminin chains, in the beta4 gene of alpha6beta4 integrin, and in the gene of collagen XVII. In dystrophic epidermolysis bullosa the tissue separation occurs beneath the basement membrane within the papillary dermis at the level of the anchoring fibrils, and several mutations have been identified in the collagen VII gene. The rapid unraveling of molecular defects in these disabling or even lethal inherited skin diseases makes possible a more precise and earlier prenatal diagnosis, creates new options for suitable therapeutic regimens, and even offers the hope of curing these diseases by means of somatic cell gene therapy.
J Mol Med (Berl) 1996 Feb
PMID:The molecular basis for inherited bullous diseases. 882 Apr 1

The Herlitz type of junctional epidermolysis bullosa (H-JEB) is a severe blistering disease affecting the skin and mucous membranes, and laminin 5 has been implicated as the candidate gene/protein system for most patients with H-JEB. In this study, we have examined a cohort of 14 families with H-JEB for mutations in the LAMB3 gene. Premature termination codon mutations were delineated in both alleles of each proband in all pedigrees. Interestingly, two recurrent mutations, R42X and R635X, were noted in over 50% of the mutant LAMB3 alleles. These nonsense mutations occurred at CpG dinucleotide sequences, suggesting hypermutability of 5-methylcytosine to thymine. Additional evidence suggested that R42X and R635X represent mutational hotspots. First, the inheritance of R635X in a homozygous individual on two different genetic backgrounds was demonstrated by haplotype analysis. Furthermore, in one family, R42X was shown to be inherited on the maternal allele which lacked this mutation, suggesting that it arose as a result of maternal germline mutation. Elucidation of these two hotspot mutations will facilitate screening of additional JEB patients for the underlying mutations.
Hum Mol Genet 1996 Feb
PMID:Mutational hotspots in the LAMB3 gene in the lethal (Herlitz) type of junctional epidermolysis bullosa. 882 79

In a distinct autosomal recessive variant of epidermolysis bullosa, EB-MD, life-long skin blistering is associated with late-onset muscular dystrophy of unknown etiology. Electron microscopy of these patients' skin suggests that tissue separation occurs intracellularly at the level of the hemidesmosomal inner plaque, which contains plectin, a high molecular weight cytoskeletal associated protein, also expressed in the sarcolemma of the muscle. In this study, we report two patients with EB-MD, each with a homozygous deletion mutation in the plectin gene, PLEC1. In the first case, the proband and her similarly affected sister had a homozygous 9 bp deletion mutation, designated as 2719de19, which resulted in elimination of three amino acids, QEA, in a sequence of 23 amino acids entirely conserved between the mouse and human sequences. The proband in the second family demonstrated a single nucleotide deletion at position 5866, designated as 5866delC, which resulted in frameshift and a premature termination codon for translation 16 bp downstream from the site of deletion. The absence of plectin in the hemidesmosomes, as reflected by negative immunofluorescence with an anti-plectin antibody (HD-1), associated with fragility of basal keratinocytes, implicates plectin as critical for binding of intermediate keratin filament network to hemidesmosomal complexes. The function of plectin as a putative attachment protein also in the muscle would explain the clinical phenotype consisting of cutaneous fragility and muscular dystrophy in EB-MD.
Hum Mol Genet 1996 Oct
PMID:Homozygous deletion mutations in the plectin gene (PLEC1) in patients with epidermolysis bullosa simplex associated with late-onset muscular dystrophy. 889 87

Ultrastructural examination of the cutaneous basement membrane zone (BMZ) reveals the presence of several attachment structures, which are critical for integrity of the stable association of epidermis and dermis. These include hemidesmosomes which extend from the intracellular compartment of the basal keratinocyte to the underlying basement membrane where they complex with anchoring filaments, thread-like structures traversing the lamina lucida. At the lower portion of dermal-epidermal attachment zone, anchoring fibrils extend from the lamina densa to the papillary dermis, where they associate with basement membrane-like structures, known as anchoring plaques. Molecular cloning of the cutaneous BMZ components has allowed elucidation of the structural features of the proteins which constitute these attachment structures. Specifically, hemidesmosomes have been shown to consist of at least four distinct proteins. The intracellular hemidesmosomal inner plaque is comprised of the 230-kD bullous pemphigoid antigen (BPAG1), and plectin, a high-molecular weight cytomatrix protein, encoded by the corresponding gene, PLEC1. The transmembrane component of the hemidesmosomes consists of the 180-kD bullous pemphigoid antigen (BPAG2), a collagenous protein also known as type XVII collagen (COL17A1), as well as of the basal keratinocyte-specific integrin alpha 6 beta 4. The anchoring filaments consist predominantly of laminin 5 with three constitutive subunit polypeptides, the alpha 3, beta 3 and gamma 2 chains, which is associated with laminin 6 with the chain composition alpha 3, beta 1 and gamma 1. Also associated with anchoring filaments is a novel protein, ladinin, which serves as autoantigen in the linear IgA disease, and the corresponding gene, LAD1, has been mapped to human chromosome 1. Finally, the major, if not the exclusive, component of anchoring fibrils is type VII collagen, encoded by the gene (COL7A1) which consists of 118 distinct exons, the largest number of exons in any gene published thus far. Collectively, the cutaneous basement membrane zone is a complex continuum of macromolecules which form a network providing the stable association of the epidermis to the underlying dermis. Thus, genetic lesions resulting in abnormalities in any part of this network could result in a blistering skin disease, such as epidermolysis bullosa.
Mol Biol Rep 1996
PMID:Molecular complexity of the cutaneous basement membrane zone. 898 17


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