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Frances J D Smith

Publications and source records attributed to Frances J D Smith.

16 recordsLinked to original sources
PubMed2006

Prevalent and rare mutations in the gene encoding filaggrin cause ichthyosis vulgaris and predispose individuals to atopic dermatitis.

Mutations in the filament aggregating protein (filaggrin) gene have recently been identified as the cause of the common genetic skin disorder ichthyosis vulgaris (IV), the most prevalent inherited disorder of keratinization. The main characteristics of IV are fine-scale on the arms and legs, palmar hyperlinearity, and keratosis pilaris. Here, we have studied six Irish families with IV for mutations in filaggrin. We have identified a new mutation, 3702delG, in addition to further instances of the reported mutations R501X and 2282del4, which are common in people of European origin. A case of a 2282del4 homozygote was also identified. Mutation 3702delG terminates protein translation in filaggrin repeat domain 3, whereas both recurrent mutations occur in repeat 1. These mutations are semidominant: heterozygotes have an intermediate phenotype most readily identified by palmar hyperlinearity and in some cases fine-scale and/or keratosis pilaris, whereas homozygotes or compound heterozygotes generally have more marked ichthyosis. Interestingly, the phenotypes of individuals homozygous for R501X, 2282del4, or compound heterozygous for R501X and 3702delG, were comparable, suggesting that mutations located centrally in the filaggrin repeats are also pathogenic.

Dermatitis, Atopic↗
PubMed2006

Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.

Atopic disease, including atopic dermatitis (eczema), allergy and asthma, has increased in frequency in recent decades and now affects approximately 20% of the population in the developed world. Twin and family studies have shown that predisposition to atopic disease is highly heritable. Although most genetic studies have focused on immunological mechanisms, a primary epithelial barrier defect has been anticipated. Filaggrin is a key protein that facilitates terminal differentiation of the epidermis and formation of the skin barrier. Here we show that two independent loss-of-function genetic variants (R510X and 2282del4) in the gene encoding filaggrin (FLG) are very strong predisposing factors for atopic dermatitis. These variants are carried by approximately 9% of people of European origin. These variants also show highly significant association with asthma occurring in the context of atopic dermatitis. This work establishes a key role for impaired skin barrier function in the development of atopic disease.

Alleles↗
PubMed2006

Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris.

Ichthyosis vulgaris (OMIM 146700) is the most common inherited disorder of keratinization and one of the most frequent single-gene disorders in humans. The most widely cited incidence figure is 1 in 250 based on a survey of 6,051 healthy English schoolchildren. We have identified homozygous or compound heterozygous mutations R501X and 2282del4 in the gene encoding filaggrin (FLG) as the cause of moderate or severe ichthyosis vulgaris in 15 kindreds. In addition, these mutations are semidominant; heterozygotes show a very mild phenotype with incomplete penetrance. The mutations show a combined allele frequency of approximately 4% in populations of European ancestry, explaining the high incidence of ichthyosis vulgaris. Profilaggrin is the major protein of keratohyalin granules in the epidermis. During terminal differentiation, it is cleaved into multiple filaggrin peptides that aggregate keratin filaments. The resultant matrix is cross-linked to form a major component of the cornified cell envelope. We find that loss or reduction of this major structural protein leads to varying degrees of impaired keratinization.

Child↗
PubMed2006

SiRNA-mediated selective inhibition of mutant keratin mRNAs responsible for the skin disorder pachyonychia congenita.

RNA interference offers a novel approach for treating genetic disorders including the rare monogenic skin disorder pachyonychia congenita (PC). PC is caused by mutations in keratin 6a (K6a), K6b, K16, and K17 genes, including small deletions and single nucleotide changes. Transfection experiments of a fusion gene consisting of K6a and a yellow fluorescent reporter (YFP) resulted in normal keratin filament formation in transfected cells as assayed by fluorescence microscopy. Similar constructs containing a single nucleotide change (N171K) or a three-nucleotide deletion (N171del) showed keratin aggregate formation. Mutant-specific small inhibitory RNAs (siRNAs) effectively targeted these sites. These studies suggest that siRNAs can discriminate single nucleotide mutations and further suggest that "designer siRNAs" may allow effective treatment of a host of genetic disorders including PC.

Cell Line, Tumor↗
PubMed2005

Clinical and pathological features of pachyonychia congenita.

Pachyonychia congenita (PC) is a rare genodermatosis affecting the nails, skin, oral mucosae, larynx, hair, and teeth. Pathogenic mutations in keratins K6a or K16 are associated with the PC-1 phenotype whereas K6b and K17 mutations are associated with the PC-2 phenotype. Analysis of clinical, pathological, and genetic data from the literature and two research registries reveal that >97% of PC cases exhibit fingernail and toenail thickening, and painful plantar keratoderma. Prospective evaluation of 57 PC patients from 41 families revealed variable clinical findings: hyperhidrosis (79%), oral leukokeratosis (75%), follicular keratosis (65%), palmar keratoderma (60%), cutaneous cysts (35%), hoarseness or laryngeal involvement (16%), coarse or twisted hair (26%), early primary tooth loss (14%), and presence of natal or prenatal teeth (2%). Stratification of these data by keratin mutation confirmed the increased incidence of cyst formation and natal teeth among PC-2 patients, although cysts were more commonly seen in PC-1 than previously reported (25%-33%). Previously unreported clinical features of PC include development of painful oral and nipple lesions during breastfeeding, copious production of waxy material in ears, and inability to walk without an ambulatory aid (50%). Possible pathogenic mechanisms are discussed with respect to the clinicopathologic and genetic correlations observed.

Darier Disease↗
PubMed2005

The genetic basis of pachyonychia congenita.

In 1994, the molecular basis of pachyonychia congenita (PC) was elucidated. Four keratin genes are associated with the major subtypes of PC: K6a or K16 defects cause PC-1; and mutations in K6b or K17 cause PC-2. Mutations in keratins, the epithelial-specific intermediate filament proteins, result in aberrant cytoskeletal networks which present clinically as a variety of epithelial fragility phenotypes. To date, mutations in 20 keratin genes are associated with human disorders. Here, we review the genetic basis of PC and report 30 new PC mutations. Of these, 25 mutations were found in PC-1 families and five mutations were identified in PC-2 kindreds. All mutations identified were heterozygous amino acid substitutions or small in-frame deletion mutations with the exception of an unusual mutation in a sporadic case of PC-1. The latter carried a 117 bp duplication resulting in a 39 amino acid insertion in the 2B domain of K6a. Also of note was mutation L388P in K17, which is the first genetic defect identified in the helix termination motif of this protein. Understanding the genetic basis of these disorders allows better counseling for patients and paves the way for therapy development.

Base Sequence↗
PubMed2005

Insights into genotype-phenotype correlation in pachyonychia congenita from the human intermediate filament mutation database.

Keratins are the intermediate filament proteins specifically expressed by epithelial cells. The Human Genome Project has uncovered a total of 54 functional keratin genes that are differentially expressed in specific epithelial structures of the body, many of which involve the epidermis and its appendages. Pachyonychia congenita (PC) is a group of autosomal dominant genodermatoses affecting the nails, thick skin and other ectodermal structures, according to specific sub-type. The major clinical variants of the disorder (PC-1 and PC-2) are known to be caused by dominant-negative mutations in one of four differentiation-specific keratins: K6a, K6b, K16, and K17. A total of 20 human keratin genes are currently linked to single-gene disorders or are predisposing factors in complex traits. In addition, a further six intermediate filament genes have been linked to other non-epithelial genetic disorders. We have established a comprehensive mutation database that catalogs all published independent occurrences of intermediate filament mutations (http://www.interfil.org), with details of phenotypes, published papers, patient support groups and other information. Here, we review the genotype-phenotype trends emerging from the spectrum of mutations in these genes and apply these correlations to make predictions about PC phenotypes based on the site of mutation and keratin pair involved.

Age of Onset↗
PubMed2004

Novel mechanism of revertant mosaicism in Dowling-Meara epidermolysis bullosa simplex.

The severe Dowling-Meara form of epidermolysis bullosa simplex is caused by dominant-negative mutations in keratins 5 and 14, which are specifically expressed in the basal keratinocytes of the epidermis. The most common mutation in the Dowling-Meara form of epidermolysis bullosa simplex patients is the missense mutation R125C in exon 1 of the K14 gene. We made a primary keratinocyte cell line from a sporadic case known to carry the R125C mutation as part of an ongoing gene therapy initiative. The full-length K14 cDNA was sequenced using keratinocyte mRNA. Unexpectedly, a second mutation was identified in K14: a heterozygous 1 bp insertion mutation (242insG) upstream of the R125C mutation. This frameshift mutation creates a premature termination codon immediately downstream, thereby nullifying the dominant-negative allele. The second mutation was only present in DNA derived from keratinocytes and was absent from lymphocyte DNA. This case represents a novel mechanism of revertant mosaicism and is an example of "natural gene therapy".

3T3 Cells↗
PubMed2004

Recurrent mutations in kindlin-1, a novel keratinocyte focal contact protein, in the autosomal recessive skin fragility and photosensitivity disorder, Kindler syndrome.

Kindler syndrome (OMIM 173650) is a rare autosomal recessive disorder characterized by trauma-induced blister formation (especially in childhood) and photosensitivity. Other features include mucocutaneous scarring and progressive poikiloderma. There is also an increased risk of skin and mucous membrane malignancy. The disorder was recently mapped to 20p12.3 and pathogenic mutations were identified in a new gene, KIND1. This gene encodes a 677 amino acid protein, kindlin-1, a component of focal contacts in keratinocytes. In this study, we identified four new recurrent mutations in KIND1 in 16 individuals with Kindler syndrome from 13 families of Pakistani (676insC), UK Caucasian (E304X), Omani (W616X), or Italian (958-1G > A) origins. Haplotype analysis demonstrated common ancestral mutant alleles for each mutation, apart from one of the six Pakistani families in which the mutation 676insC (which occurs in a repeat of seven cytosines) was present on a different genetic background. All mutations were homozygous, apart from the three UK Caucasian cases that were all compound heterozygotes (second allele mutations: L302X, 1161delA, 1909delA). All mutations were associated with markedly reduced or absent skin immunostaining with an antikindlin-1 antibody. These loss-of-function KIND1 mutations demonstrate the importance of kindlin-1 in maintaining epithelial integrity, although the mechanism linking this mutant protein to photosensitivity and poikiloderma remains to be determined. Delineation of these recurrent mutations is also relevant to optimizing mutation detection strategies in Kindler syndrome patients from particular ethnic backgrounds.

Adult↗
PubMed2003

An unusual N-terminal deletion of the laminin alpha3a isoform leads to the chronic granulation tissue disorder laryngo-onycho-cutaneous syndrome.

Laryngo-onycho-cutaneous (LOC or Shabbir) syndrome (OMIM 245660) is an autosomal recessive epithelial disorder confined to the Punjabi Muslim population. The condition is characterized by cutaneous erosions, nail dystrophy and exuberant vascular granulation tissue in certain epithelia, especially conjunctiva and larynx. Genome-wide homozygosity mapping localized the gene to a 2 Mb region on chromosome 18q11.2 with an LOD score of 19.8 at theta=0. This region includes the laminin alpha3 gene (LAMA3), in which loss-of-expression mutations cause the lethal skin blistering disorder Herlitz junctional epidermolysis bullosa. Detailed investigation showed that this gene possesses a further 38 exons (76 exons in total) spanning 318 kb of genomic DNA, and encodes three distinct proteins, designated laminin alpha3a, alpha3b1 and alpha3b2. The causative mutation in 15 families was a frameshift mutation 151insG predicting a stop codon 7 bp downstream in an exon that is specific to laminin alpha3a. This protein is secreted only by the basal keratinocytes of stratified epithelia, implying that LOC is caused by dysfunction of keratinocyte-mesenchymal communication. Surprisingly, the 151insG mutation does not result in nonsense-mediated mRNA decay due to rescue of the transcript by an alternative translation start site 6 exons downstream. The resultant N-terminal deletion of laminin alpha3a was confirmed by immunoprecipitation of secreted proteins from LOC keratinocytes. These studies show that the laminin alpha3a N-terminal domain is a key regulator of the granulation tissue response, with important implications not only in LOC but in a range of other clinical conditions associated with abnormal wound healing.

Chromosomes, Human, Pair 18↗
PubMed2003

Loss of kindlin-1, a human homolog of the Caenorhabditis elegans actin-extracellular-matrix linker protein UNC-112, causes Kindler syndrome.

Kindler syndrome is an autosomal recessive disorder characterized by neonatal blistering, sun sensitivity, atrophy, abnormal pigmentation, and fragility of the skin. Linkage and homozygosity analysis in an isolated Panamanian cohort and in additional inbred families mapped the gene to 20p12.3. Loss-of-function mutations were identified in the FLJ20116 gene (renamed "KIND1" [encoding kindlin-1]). Kindlin-1 is a human homolog of the Caenorhabditis elegans protein UNC-112, a membrane-associated structural/signaling protein that has been implicated in linking the actin cytoskeleton to the extracellular matrix (ECM). Thus, Kindler syndrome is, to our knowledge, the first skin fragility disorder caused by a defect in actin-ECM linkage, rather than keratin-ECM linkage.

Abnormalities, Multiple↗
PubMed2003

Clouston syndrome can mimic pachyonychia congenita.

We studied three families suffering from nail abnormalities who had previously been diagnosed as pachyonychia congenita. No keratin gene mutations were detected. Sequencing of connexin 30 (GJB6 gene) in these patients identified heterozygous missense mutations G11R and A88V that are known to be associated with Clouston syndrome. This unexpected finding expands the Clouston syndrome phenotype and suggests that some patients diagnosed with pachyonychia may in fact be suffering from Clouston syndrome.

Adolescent↗
PubMed2002

Cloning of human, murine, and marsupial keratin 7 and a survey of K7 expression in the mouse.

Keratins are cytoplasmic intermediate filament proteins expressed by epithelial cells. Keratin 7 (K7) is expressed in a wide range of epithelial structures in humans. We have cloned and fully sequenced the human and mouse K7 genes and mRNAs, and the K7 mRNA from the marsupial Potorous tridactylis, from which the widely used simple epithelial cell lines PtK1 and PtK2 are derived. Percentage identity plots comparing the mouse and human genomic sequences revealed a number of conserved CpG islands associated with the K7 gene. There was considerable conservation of introns between the two species, which may indicate the presence of intronic regulatory elements. Only the most proximal 500bp of the promoter was conserved, although an additional conserved sequence island was found 2-3kb upstream. Protein sequence comparisons between the three species allowed identification of conserved regions of the keratin variable domains that may be candidates for protein-protein interactions and/or regulatory modification. From the mouse sequence, we generated a polyclonal rabbit antibody specific for murine K7. This antibody was used to perform a survey of K7 expression in the mouse. The expression pattern was similar to the reported human distribution, with substantial expression observed in lung, bladder, mesothelium, hair follicle, and ductal structures. We also noted previously unreported expression of K7 in the gastrointestinal tract and filiform papillae of the tongue and specific K7 expression in a range of "hard" epithelial tissues. The distribution of K7 in mouse and availability of genomic sequence from the 129/Sv mouse strain will allow the generation and analysis of transgenic mice expressing mutant forms of K7 and to predict the phenotype of human genetic disorders caused by mutations in this keratin.

Amino Acid Sequence↗
PubMed2002

A novel connexin 30 mutation in Clouston syndrome.

Clouston syndrome (hidrotic ectodermal dysplasia) is an autosomal dominant ectodermal dysplasia characterized by alopecia, palmoplantar hyperkeratosis, and nail dystrophy. Recently, mutations in the GJB6 gene encoding the gap junction protein connexin 30 have been shown to cause this disorder. To date, all mutations have involved two codons: G11R and A88V. Here, we report a novel mutation V37E within the first transmembrane domain of connexin 30 in a spontaneous case of Clouston syndrome. The mutation was detected in genomic DNA, confirmed in reverse transcription polymerase chain reaction products, and was excluded from 100 ethnically matched control individuals by restriction enzyme analysis.

Adult↗