Keratin 16 and keratin 17 mutations cause pachyonychia congenita.

Pachyonychia congenita (PC) is a group of autosomal dominant disorders characterized by dystrophic nails and other ectodermal aberrations. A gene for Jackson-Lawler PC was recently mapped to the type I keratin cluster on 17q. Here, we show that a heterozygous missense mutation in the helix initiation motif of K17 (Asn92Asp) co-segregates with the disease in this kindred. We also show that Jadassohn-Lewandowsky PC is caused by a heterozygous missense mutation in the helix initiation peptide of K16 (Leu130Pro). The known expression patterns of these keratins in epidermal structures correlates with the specific abnormalities observed in each form of PC.

Autosomal dominant junctional epidermolysis bullosa.

BACKGROUND: Epidermolysis bullosa (EB) encompasses a heterogeneous group of inherited skin disorders associated with trauma-induced blistering. The junctional forms of EB (JEB), Herlitz JEB, non-Herlitz JEB and JEB associated with pyloric atresia have all been attributed to autosomal recessive inheritance. We describe a 7-year-old girl with defective dental enamel, trauma-induced blistering and subsequent scarring. Her mother, a carrier of the mutation p.G627V in the collagen XVII gene (COL17A1) had evidence of hypoplastic dental enamel without skin blistering. Her grandmother had non-Herlitz JEB as a result of a compound heterozygous mutation in COL17A1 (p.G627V and c.3514ins25). OBJECTIVES: To explore the molecular, ultrastructural and immunofluorescence findings of the first case of dominant JEB. METHODS: Mutational analysis of COL17A1 was performed on the proband's genomic DNA. In addition, transmission electron microscopy and immunofluorescence microscopy were performed on a nonlesional skin biopsy from the proband and an unrelated healthy control. RESULTS: Direct sequencing revealed a heterozygous glycine substitution mutation, p.G627V, in COL17A1. No discernible morphological abnormalities were found on transmission electron microscopy; however, immunofluorescence microscopy revealed findings of an altered distribution pattern for type XVII collagen epitopes close to the dermal-epidermal junction. CONCLUSION: This report describes the first case of dominant JEB. Although some heterozygous mutations in COL17A1 are known to cause dental abnormalities none were associated with skin fragility. The dominant-negative interference between the proband's mutated type XVII collagen and the wild-type allele appears to render the skin prone to trauma-induced blister formation. Alternatively, other undisclosed modifying genetic or epigenetic factors might explain why the patient gets blistering whereas her mother, who has the same COL17A1 mutation, has no skin fragility.

Loricrin mutation in Vohwinkel's keratoderma is unique to the variant with ichthyosis.

A mutation in the glycine-rich cornified envelope protein loricrin has recently been reported in Vohwinkel's keratoderma (honeycomb keratoderma with pseudoainhum), in a pedigree amongst whom ichthyosis was also a feature. We have studied two further families with Vohwinkel's keratoderma for evidence ofloricrin mutations. Our first family (VK1) also had ichthyosis but not deafness. In lesional and nonlesional skin, granular and transitional cell layers were increased. In immunoelectron-microscopic studies cornified envelopes were abnormally thin and were labeled densely by anti-involucrin antibodies, but only sparsely by antiloricrin antibodies; however, abnormal intranuclear granules seen in granular and cornified layer cells were labeled by antibodies to both C- and N-terminal loricrin. Microsatellite markers in VK1 supported linkage to the loricrin locus in the epidermal differentiation complex at 1q21 (Zmax = 2.48). The loricrin gene was sequenced, identifying a heterozygous mutation as previously reported: a G insertion producing a frameshift after codon 231 and an abnormal C-terminal peptide lacking residues necessary for cross-linking. In our second family (VK2), affected members had sensorineural deafness but not ichthyosis. Immunoelectron-microscopic studies showed normal loricrin distribution, and assuming complete penetrance, linkage to 1q21 was excluded. Vohwinkel's keratoderma is thus clinically and genetically heterogeneous. Only the variant with ichthyosis appears to be due to loricrin mutation. As the arginine-rich domain in C-terminal loricrin caused by the frameshift contains several potential bipartite nuclear localization signals, we suggest that the intranuclear accumulation of loricrin in VK1 is due to these motifs, and may be unique to insertional mutation.

Striate palmoplantar keratoderma resulting from desmoplakin haploinsufficiency.

Recently, the first example of a human mutation in the gene encoding the desmosomal plaque protein, desmoplakin, has been described in a patient with autosomal dominant striate palmoplantar kerato-derma. We now report a further case of a desmoplakin mutation in a proband with striate palmoplantar keratoderma that also results in a null allele and haploinsufficiency. The mutation was a heterozygous G > A transition at the donor + 1 site of intron 7 of the desmoplakin gene (939 + 1 G > A; Genbank M77830). The aberrant splicing leads to retention of the entire intron 7, which contains a premature termination codon within the N-terminal domain of the peptide. Because the mutant null allele could not be identified on cDNA sequencing, we determined by polymerase chain reaction the exon-intron organization of the desmoplakin gene to facilitate analysis of genomic DNA. The gene spans approximately 45 kb of chromosome 6 and comprises 24 exons ranging in size from 51 bp to 3922 bp. We have also characterized fully the 3'UTR of the desmoplakin cDNA. This study demonstrates the relevance of haploinsufficiency for desmoplakin in the pathogenesis of this genodermatosis. Assessment of family members bearing the mutant allele also emphasizes the significance of an individual's age and exposure to skin trauma in manifesting full phenotypic expression of the disorder.

Identification of a novel mutation R42P in the gap junction protein beta-3 associated with autosomal dominant erythrokeratoderma variabilis.

We report a missense mutation in the gap junction protein beta-3 (encoding Connexin 31), which was detected in only the affected members of a family in which the autosomal dominant skin disease erythrokeratoderma variabilis was segregating. The nucleotide change results in an arginine to proline substitution in codon 42. This residue is positioned on the first transmembrane/first extracellular domain of the gap junction protein with the mutation replacing a negatively charged residue with a nonpolar residue. This change may disrupt the conformation of the protein and voltage gating polarity leading to impaired channel function.

Novel splice site mutation in keratin 1 underlies mild epidermolytic palmoplantar keratoderma in three kindreds.

We report a novel mutation in the exon 6 splice donor site of keratin 1 (G4134A) that segregates with a palmoplantar keratoderma in three kindreds. The nucleotide substitution leads to the utilization of a novel in-frame splice site 54 bases downstream of the mutation with the subsequent insertion of 18 amino acids into the 2B rod domain. This mutation appears to have a milder effect than previously described mutations in the helix initiation and termination sequence on the function of the rod domain, with regard to filament assembly and stability. Affected individuals displayed only mild focal epidermolysis in the spinous layer of palmoplantar epidermis, in comparison with cases of bullous congenital ichthyosiform erythroderma also due to keratin 1 mutations, which show widespread and severe epidermolysis. This study describes a novel mutation in KRT1 that results in a phenotype distinct from classical bullous congenital ichthyosiform erythroderma.

Mutations in the rod 1A domain of keratins 1 and 10 in bullous congenital ichthyosiform erythroderma (BCIE).

Bullous congenital ichthyosiform erythroderma is a human hereditary skin disorder in which suprabasal keratinocytes rupture. Recent reports have implicated keratins K1 and K10 in this disease. Here we describe four diverse keratin mutations that are all significantly associated with this disease. Two of these are in the helix 1A subdomain of the type II keratin 1, giving a serine-to-proline substitution in codon 185 and an asparagine-to-serine substitution in codon 187. In the analogous region of type I keratin 10, an arginine-to-proline and an arginine-to-serine transition in codon 156 have been identified. All four mutations create restriction fragment length polymorphisms that were used exclude the mutations from 120 normal chromosomes. Insertional polymorphism (in the V2 subdomains of the non-helical tails of K1 and K10) was excluded as the cause of the phenotypic heterogeneity observed within one family.

Spectrum of dominant mutations in the desmosomal cadherin desmoglein 1, causing the skin disease striate palmoplantar keratoderma.

The adhesive proteins of the desmosome type of cell junction consist of two types of cadherin found exclusively in that structure, the desmogleins and desmocollins, coded by two closely linked loci on human chromosome 18q12.1. Recently we have identified a mutation in the DSG1 gene coding for desmoglein 1 as the cause of the autosomal dominant skin disease striate palmoplantar keratoderma (SPPK) in which affected individuals have marked hyperkeratotic bands on the palms and soles. In the present study we present the complete exon-intron structure of the DSG1 gene, which occupies approximately 43 kb, and intron primers sufficient to amplify all the exons. Using these we have analysed the mutational changes in this gene in five further cases of SPPK. All were heterozygotic mutations in the extracellular domain leading to a truncated protein, due either to an addition or deletion of a single base, or a base change resulting in a stop codon. Three mutations were in exon 9 and one in exon 11, both of which code for part of the third and fourth extracellular domains, and one was in exon 2 coding for part of the prosequence of this processed protein. This latter mutation thus results in the mutant allele synthesising only 25 amino acid residues of the prosequence of the protein so that this is effectively a null mutation implying that dominance in the case of this mutation was caused by haploinsufficiency. The most severe consequences of SPPK mutations are in regions of the body where pressure and abrasion are greatest and where desmosome function is most necessary. SPPK therefore provides a very sensitive measure of desmosomal function.

Ultrastructural features of the osteoid of patients with fibrogenesis imperfecta ossium.

The osteoid of a patient with Fibrogenesis Imperfecta Ossium is described. Three iliac crest biopsies were taken; firstly before treatment, secondly after calcitriol therapy and finally after successful treatment with melphalan and prednisolone. In the pretreatment biopsy the osteoid was greatly enlarged, showed complete absence of the birefringence characteristic of oriented collagen fibers, and at ultrastructural level was shown to be composed of abnormal collagen fibrils. The fibrils were often curved and were extremely variable in thickness. Calcification within the osteoid took the form of calcospherites and spread of calcification from these to collagen fibrils was greatly delayed. In the second biopsy two aspects of osteoid ultrastructure were noted; some samples resembled the first biopsy, but others had a different organization. The osteoid of these samples had two regions: an inner region containing abnormal collagen fibrils and an outer region composed of moderately electron-dense amorphous material. The osteoblasts associated with this region were clearly highly biosynthetically active. The third biopsy, after treatment with Melphalan and prednisolone, showed a reversion to more normal bone ultrastructure with uniform, oriented collagen fibrils and prompt mineralization resulting in narrow osteoid seams. Remnants of the original abnormal osteoid were present in the marrow space as calcified debris. Reasons for the success of this therapeutic regime are unclear; however, some speculation is made as to the possible roles of the cytotoxic drug and the glucocorticoid in the regression of this condition.

The composition of wide-spaced collagen in normal and diseased Descemet's membrane.

Descemet's membrane, the specialised basement membrane of the corneal endothelium, contains a form of extracellular matrix described as wide-spaced collagen. In healthy human Descemet's membrane, wide-spaced collagen forms a highly ordered array in a region called the anterior banded zone. However, in corneal endotheliopathies such as Fuchs' endothelial dystrophy and the iridocorneal-endothelial syndrome large amounts of wide-spaced collagen are deposited posterior to Descemet's membrane in a grotesque parody of the anterior banded zone termed a posterior collagenous layer. The purpose of this study was to identify the composition of the wide-spaced collagen found in the Descemet's membrane of normal and diseased human corneas. Tissue from three normal human corneas, three from patients with Fuchs' endothelial dystrophy and five from patients with the iridocorneal-endothelial syndrome was prepared for immuno-electron microscopy by freezing or embedding in Lowicryl K4M resin. Immunocytochemistry on ultrathin sections was performed with antibodies to collagen Types I, III, V, VI and VIII, fibronectin, laminin, P component and tenascin. Ultrastructural labelling of the wide-spaced collagen in the anterior banded zone of normal and diseased corneas and also of the wide-spaced collagen in the posterior collagenous layer of all the diseased corneas was demonstrated with antibody to collagen Type VIII. Wide-spaced collagen was not labelled by any of the other antibodies used. Large amounts of Type VIII collagen are present in discrete regions of healthy and diseased Descemet's membrane. The deposition of Type VIII collagen may significantly influence the pathobiology of the corneal endotheliopathies.

Expression in yeast of amino-terminal peptide fusions to hepatitis B core antigen and their immunological properties.

Hepatitis B core protein (HBcAg) is a potent antigen that gives both a T-cell-dependent and a T-cell-independent antibody response. It has been shown that a foreign epitope can be fused to the amino terminus of HBcAg without affecting particle integrity, and that the resulting chimaeric cores retain the immunogenicity of the foreign epitope. Here we describe the efficient expression in yeast of two different chimaeric cores, carrying epitopes of Foot and Mouth Disease Virus (FMDV) or human chorionic gonadotrophin (hCG), which are candidates for FMD and contraceptive vaccines, respectively. These cores could not be produced in E. coli in soluble form but were expressed to high levels in yeast. We constructed a yeast expression vector that allows rapid production of different chimaeric cores by cloning in cassettes encoding foreign epitopes. Both FMDV and hCG-cores were shown to present the epitopes at the surface of the particles. The FMDV-cores produced in yeast were efficient inducers of neutralising antibodies in guinea-pigs after one low dose.

Prenatal diagnosis for severe inherited skin disorders: 25 years' experience.

BACKGROUND: Over the last 25 years there have been major advances in methods for prenatal testing of inherited skin disorders. Since 1979, our group at the St John's Institute of Dermatology has performed 269 prenatal diagnoses, using a variety of approaches, including fetal skin biopsy (FSB), chorionic villus sampling (CVS) and preimplantation genetic diagnosis (PGD). OBJECTIVES: This study was designed to review the clinical indications, testing procedures and laboratory analyses for all prenatal tests conducted at St John's over this period. METHODS: FSBs were examined for morphological and, when relevant or feasible, immunohistochemical abnormalities. The DNA-based tests involved screening by nucleotide sequencing, restriction enzyme digests or, in a few cases, by linkage analysis. Results Of the 269 tests, 191 were FSB, 76 were CVS and two were PGD. The major indications for FSB were epidermolysis bullosa (EB) (138 cases, including 88 junctional and 48 dystrophic), ichthyoses (37 cases, including 22 tests for harlequin ichthyosis) and oculocutaneous albinism (12 cases). Of the CVS procedures, 75 were for EB (40 junctional, 35 dystrophic) and one was for the EEC (ectrodactyly, ectodermal dysplasia, clefting) syndrome. Both of the PGD procedures were for the skin fragility-ectodermal dysplasia syndrome. All tests provided accurate diagnoses and the fetal loss rate was approximately 1% for both FSB and CVS. CONCLUSIONS: The development of prenatal testing has proved to be of great benefit for individuals or couples at risk of having children with severe inherited skin disorders and, in the absence of a cure, prenatal testing along with appropriate counselling has become an important translational benefit of basic research and an integral part of clinical management.

Transient bullous dermolysis of the newborn in three generations.

Transient bullous dermolysis of the newborn (TBDN) is a rare form of dystrophic epidermolysis bullosa (DEB) that presents with neonatal skin blistering but which usually improves markedly during early life or even remits completely. Skin biopsies reveal abnormal intraepidermal accumulation of type VII collagen which results in poorly constructed anchoring fibrils and a sublamina densa plane of blister formation. The reason for the spontaneous clinical improvement is not known, but there is a gradual recovery in type VII collagen secretion from basal keratinocytes to the dermal-epidermal junction, with subsequent improvement or correction of anchoring fibril morphology. In this report, we describe TBDN occurring in three generations of the same family. Blistering occurred only during the first few months after birth, and all affected individuals were found to have a heterozygous glycine substitution mutation in exon 45 of the type VII collagen gene, COL7A1, designated G1522E. This mutation represents the third report of a pathogenic COL7A1 mutation in TBDN. Despite limited understanding of the disease mechanism in TBDN, this distinct form of DEB is important to recognize as it typically has a benign and self-limiting course. However, not all cases of DEB associated with intraepidermal type VII collagen are 'transient'. Genetic counselling in such patients therefore should be guarded until the pathophysiology of TBDN is better understood.

Effect of patterned surfaces of adhesive islands on the shape, cytoskeleton, adhesion and behaviour of Swiss mouse 3T3 fibroblasts.

A pattern of circular islands of adhesive substratum can be used to control cell shape and behaviour. We have shown previously that the proportion of Swiss 3T3 cells that synthesize DNA varies with the area of the island to which they are attached, within the range 500-5000 microns2. In this paper we investigate the cytoskeleton and adhesions of cells on islands using a variety of techniques including phalloidin staining and interference reflection microscopy. Islands of area 2000 microns2 or less constrain cell shape, and cause focal contacts and actin microfilament bundles to accumulate in a circle at the margin. These changes are most obvious in islands of about 1000 microns2, in which a complete ring of adhesion is sometimes formed in the periphery of the cell. This peripheral distribution is less common in cells on even smaller islands, and the focal contacts become smaller and less numerous. It is not yet clear whether any of these structural changes are associated directly with the proliferative stimulus due to contact with the substratum. However, we expect that the use of patterned substrata will contribute to the study of how cell shape and structure regulate many cell functions.

Limitation of substratum size alters cytoskeletal organization and behaviour of Swiss 3T3 fibroblasts.

Cell spreading and adhesion formation in Swiss 3T3 cells was studied on circular adhesive islands of size 400-500 microns 2 made by evaporating palladium through a mask onto an underlying non-adhesive surface. Cell spreading was limited since focal contacts were restricted to the palladium. On islands less than 2000 microns 2, focal contacts and actin bundles were arranged at the cell periphery. On islands less than 1000 microns 2, the size and number of focal contacts were reduced. Focal contacts may be important regulators of proliferation, but they do not seem to form a deterministic link between substratum contact and proliferative stimulus.

Descemet's membrane in the iridocorneal-endothelial syndrome: morphology and composition.

The iridocorneal-endothelial syndrome is a disease of the ocular anterior segment characterized by corneal failure, glaucoma and iris destruction. Specular photomicroscopical and histological studies suggest the disorder is caused by a population of abnormal corneal endothelial cells. In other corneal endotheliopathies Descemet's membrane, the basement membrane underlying the endothelial cells, is disfigured by the presence of an abnormal region of extracellular matrix termed a posterior collagenous layer, which is laid down by the diseased endothelial cells. In this study we sought to establish the typical morphology and composition of Descemet's membrane in the iridocorneal-endothelial syndrome. Ultrastructural examination of Descemet's membrane in 27 keratoplasty specimens identified three morphologic patterns. In the majority there was a posterior collagenous layer which in all cases consisted of an anterior layer of wide-spaced collagen and a posterior layer of microfibrils embedded in an amorphous matrix. In four specimens which did not possess a posterior collagenous layer the anterior banded zone of Descemet's membrane was absent. In five corneas Descemet's membrane was normal. The composition of the posterior collagenous layer was examined by immunoelectron microscopy (five corneas) and histochemistry (six corneas). Collagen Types I, III, V, VI and VIII, fibronectin, tenascin and oxytalan were microfibrillar components, collagen Type VIII formed wide-spaced collagen whilst laminin was present in the amorphous matrix. The stereotyped derangements of structure and composition identified in the endothelial basement membrane may significantly influence the pathobiology of this disorder.

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.

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 Köbner (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.

Skin fragility and hypohidrotic ectodermal dysplasia resulting from ablation of plakophilin 1.

We report a 2-year-old boy with an unusual autosomal recessively inherited skin disease comprising trauma-induced skin fragility and congenital ectodermal dysplasia affecting hair, nails and sweat glands. Skin biopsy showed widening of intercellular spaces between keratinocytes and ultrastructural findings of small, poorly formed desmosomes with reduced connections to the keratin filament cytoskeleton. Immunohistochemical analysis revealed a complete absence of staining for the accessory desmosomal plaque protein plakophilin 1 (PKP1; band 6 protein). The affected individual was a compound heterozygote for null mutations on both alleles of the PKP1 gene. Both mutations occurred within the amino terminus of PKP1, the domain which normally binds the cytoskeletal keratin filament network to the cell membrane. Apart from its localization within desmosomal plaques, PKP1 may also be present within the cytoplasm and nucleus and has putative roles in signal transduction and regulation of gene activity. The clinicopathological observations in this patient demonstrate the relevance of PKP1 to desmosome formation, cutaneous cell-cell adhesion and epidermal development and demonstrate the specific manifestations of human functional knockout mutations in this gene.