DNA-based prenatal diagnosis of generalized recessive dystrophic epidermolysis bullosa in six pregnancies at risk for recurrence

COL7A1 Homozygous Arg2471Ter Mutation Leads to the Severe Phenotype of Autosomal Recessive Dystrophic Epidermolysis Bullosa in the Fetus

Introduction

Autosomal recessive dystrophic epidermolysis bullosa (RDEB) is a rare disease with an early onset and severe phenotype. The pathogenic mechanism associated with mutations in the gene COL7A1 has been widely studied and many related cases have been reported, but prenatal cases are rare. Here, we report the prenatal diagnosis of a sporadic case of RDEB.

Methods

In this study, the fetus with abnormal skin manifestations, which were determined during a prenatal ultrasound, was evaluated based on the ultrasound and autopsy findings and the results of molecular diagnostic analyses. Samples of the fetus and the parents were subjected to trio whole-exome sequencing, and in vitro functional analyses were conducted to analyze the pathogenicity of the detected mutation.

Results

During the conventional prenatal ultrasound, the fetus showed abnormal epidermal lines on both lower limbs and the plantar skin as well as an interruption of the continuity of the lateral epidermal line below the ankle of the right lower limb. Gene testing revealed a homozygous nonsense mutation in COL7A1 (c.7411C>T, p.Arg2471Ter), which gave rise to RDEB in the fetus. Further, the results of the in vitro functional experiments confirmed that the mutation might lead to protein degradation.

Conclusion

Most prenatal diagnoses of RDEB are the result of targeted molecular analyses carried out based on family history, and prenatal ultrasound reports of severe RDEB phenotypes are extremely rare. Our case suggests that the observation of abnormal epidermal lines should be given due consideration during prenatal diagnosis, as they may be a sign of possible epidermolysis bullosa.

Epidermolysis bullosa in France: management in the National Reference Center for Genodermatosis

For more than 20 years, the department of dermatology in the Necker Enfants Malades Hospital (Paris) has been organizing the coordination of an epidermolysis bullosa-specific multidisciplinary management. The French Ministry of Health distinguished this hospital as a reference center for rare diseases. MAGEC-Necker now aims to offer the best medical and social management of epidermolysis bullosa.

Diagnóstico pré-natal das genodermatoses

O diagnóstico pré-natal está indicado para algumas genodermatoses graves, como a epidermólise bolhosa distrófica recessiva e a epidermólise bolhosa juncional. A biópsia de pele fetal foi introduzida em 1980, mas não pode ser realizada antes da 15a semana de gestação. A análise do DNA fetal é método preciso e pode ser realizado mais precocemente na gestação. No entanto, deve-se conhecer a base molecular da genodermatose, e é essencial determinar a mutação e/ou marcadores informativos nas famílias com criança previamente afetada. O DNA fetal pode ser obtido pela biópsia da vilosidade coriônica ou amniocentese. O diagnóstico genético pré-implantação tem surgido como alternativa que dispensa a interrupção da gestação. Essa técnica, que envolve fertilização in vitro e teste genético do embrião. vem sendo realizada para genodermatoses em poucos centros de referência. A ultra-sonografia é exame não invasivo, mas tem uso limitado no diagnóstico pré-natal de genodermatoses. A ultrasonografia tridimensional geralmente estabelece o diagnóstico tardiamente na gestação, e há apenas relatos anedóticos de diagnóstico pré-natal de genodermatoses usando esse método.

Epidermolysis bullosa. II. Type VII collagen mutations and phenotype-genotype correlations in the dystrophic subtypes

BACKGROUND

The dystrophic forms of epidermolysis bullosa (DEB), a group of heritable blistering disorders, show considerable phenotypic variability, and both autosomal dominant and autosomal recessive inheritance can be recognised. DEB is derived from mutations in the type VII collagen gene (COL7A1), encoding a large collagenous protein that is the predominant, if not exclusive, component of the anchoring fibrils at the dermal-epidermal junction.

METHODS

The Dystrophic Epidermolysis Bullosa Research Association Molecular Diagnostics Laboratory (Philadelphia, Pennsylvania, USA), established in 1996, has analysed more than 1000 families with different forms of epidermolysis bullosa, among them 332 families with DEB. DNA specimens were subjected to mutation analysis by polymerase chain reaction (PCR) amplification of all 118 exons and flanking intronic sequences of COL7A1, followed either by heteroduplex scanning and sequencing of the PCR products demonstrating heteroduplexes or by direct nucleotide sequencing.

RESULTS

355 mutant alleles out of the anticipated 438 (81.1%) were disclosed. Among these mutations, a total of 242 mutations were distinct and 138 were novel, previously unreported mutations. No evidence of mutations in any other gene was obtained.

DISCUSSION

Examination of the mutation database suggested phenotype-genotype correlations, contributing to the improved subclassification of DEB with prognostic implications. The mutation information also forms the basis for accurate genetic counselling and prenatal diagnosis in families at risk for recurrence.

Single cell PCR amplification of microsatellites flanking the COL7A1 gene and suitability for preimplantation genetic diagnosis of Hallopeau–Siemens recessive dystrophic epidermolysis bullosa

BACKGROUND

Hallopeau-Siemens recessive dystrophic epidermolysis bullosa (HS-RDEB) is a severe inherited blistering skin disorder caused by mutations in the anchoring fibril type VII collagen gene, COL7A1. There is currently no effective treatment but DNA-based prenatal testing in families at risk of recurrence is possible, mostly involving chorionic villus sampling at 10-11 weeks' gestation.

OBJECTIVES

An alternative method, for avoiding recurrence of HS-RDEB, is preimplantation genetic diagnosis (PGD). This involves DNA analysis of single blastomeres extracted from late cleavage stage embryos following in vitro fertilisation.

METHODS

To establish PGD for HS-RDEB, we designed and optimised a sensitive single cell semi-duplex polymerase chain reaction (PCR) assay for two highly polymorphic dinucleotide repeat microsatellite markers, D3S1581 (telomeric) and D3S1289 (centromeric), close to the COL7A1 gene.

RESULTS

We demonstrated high PCR efficiency, low allele drop out rates and no contamination in testing this assay on 50 single buccal cells of known heterozygous genotype and 13 research blastomeres from donated embryos.

CONCLUSIONS

This semi-duplex PCR method provides robust, reproducible and informative amplification results for single cells. Moreover, this test has now been approved for clinical application by the UK Human Fertilisation and Embryology Authority (HFEA). As such, the development of PGD for HS-RDEB broadens the range of prenatal testing options and personal choice for couples at reproductive risk of this severe genetic skin disease.

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.

Prenatal diagnosis of Herlitz junctional epidermolysis bullosa in nonidentical twins

Advances in molecular diagnostics have led to the feasibility of DNA-based prenatal testing in families at risk for recurrence of severe forms of both dystrophic and junctional epidermolysis bullosa. In this report, we describe prenatal testing in a woman who previously had a child affected with Herlitz junctional epidermolysis bullosa. However, in her second pregnancy, she was found to have dichorionic diamniotic twins. DNA analysis of a pathogenic mutation and informative intragenic polymorphisms (LAMB3 gene) predicted one fetus to be affected and the other unaffected. Selective termination of the affected fetus was performed, and pregnancy with the unaffected fetus was continued, leading to full term delivery of a healthy girl with no skin blisters. This is the first reported case of DNA analysis in a twin pregnancy at risk of Herlitz junctional epidermolysis bullosa, with successful diagnosis and selective termination of one affected twin.

Prenatal diagnosis for epidermolysis bullosa: a study of 144 consecutive pregnancies at risk

Epidermolysis bullosa (EB) is a group of inherited disorders characterized by increased skin fragility, resulting in blisters and erosions after minor trauma. Mutations in 10 structural genes expressed in the cutaneous basement membrane zone have been reported. The DebRA Molecular Diagnostics Laboratory at Jefferson Medical College has performed 144 DNA-based prenatal diagnoses since 1993 in families at risk for recurrence of the most severe forms of EB, including the recessive dystrophic EB (RDEB), junctional EB (JEB), EB with pyloric atresia (EB-PA), and EB simplex (EBS). A mutation-detection strategy using either conformation-sensitive gel electrophoresis (CSGE) or denaturing high-performance liquid chromatography (dHPLC) scanning analysis, followed by nucleotide sequencing, was applied to most cases with DEB and to all JEB, EB-PA, and EBS families. For some RDEB families, linkage analysis was performed, either alone when the inheritance pattern was clear or in combination with one mutation. Among the 144 prenatal diagnoses, 63 were for RDEB, 69 for JEB, 6 for EB-PA, and 6 for EBS. Twenty-eight normal, 73 heterozygous carrier, and 28 affected RDEB, JEB, and EB-PA pregnancies were reported in these recessively inherited diseases. Two affected and four normal pregnancies were predicted in dominantly inherited EBS. Among the 144 pregnancies, 9 were terminated without confirmation, 13 cases were lost to follow-up, and 6 pregnancies are ongoing. There were 6 families with inconclusive results due either to recombination events between flanking markers, absence of informative markers for one allele, or lack of sample from the previously affected child. There were three discordant results, one that was explained by maternal contamination of the chorionic villus sample and two that were unresolved. Overall, the availability, relative ease, and over 98% success rate make molecular DNA-based prenatal diagnosis a viable option for EB families at risk.

Genética Molecular das Epidermólises Bolhosas

O estudo das alterações moleculares das epidermólises bolhosas tem contribuído para que se compreenda melhor essas enfermidades. Na epidermólise bolhosa simples a maioria dos casos está associada com alteração nas citoqueratinas basais 5 (gen KRT5) e 14 (gen KRT14), o que modifica o citoesqueleto na camada basal da epiderme, levando à degeneração dessa camada, formando bolha intra-epidérmica. Mutações na plectina (gen PLEC1), componente da placa interna do hemidesmossoma, levam também à clivagem intra-epidérmica. Na epidermólise bolhosa juncional vários gens estão envolvidos, em decorrência da complexidade da zona da membrana basal, todos levando ao descolamento dos queratinócitos basais na lâmina lúcida, pela disfunção da aderência entre esses e a lâmina densa. Alterações na laminina 5 (gens LAMA3, LAMB3 e LAMC2), integrina alfa6beta4 (gens ITGA6 e ITGB4) e colágeno XVII (gen COL17A1) foram descritas. Por fim, na epidermólise bolhosa distrófica apenas um gen está mutado, alterando o colágeno VII (gen COL7A1), principal componente das fibrilas ancorantes, produzindo clivagem abaixo da lâmina densa, variando fenotipicamente de acordo com a conseqüência da mutação. Outra aplicação importante dessas informações refere-se ao diagnóstico pré-natal, com a perspectiva no futuro da terapia gênica.

The genodermatoses: candidate diseases for gene therapy

Tremendous progress has been made in understanding the genetic basis of different forms of genodermatoses, a group of heritable diseases displaying a spectrum of phenotypic manifestations and clinical severity. The information about the underlying mutations in the candidate gene/protein systems has provided the basis for initial development of cutaneous gene therapy, and these heritable conditions appear to serve as appropriate candidate diseases for such efforts. Because of its accessibility and the fact that resident skin cells, such as epidermal keratinocytes and dermal fibroblasts, can be readily propagated in culture, skin serves as an appropriate target tissue for gene therapy. Various strategic considerations, including the use of in vivo or ex vivo approaches, gene replacement versus gene repair, utilization of different delivery systems, etc., require careful prioritization depending on the type of mutations and their pathogenetic consequences at the mRNA and protein levels.

Prenatal diagnosis of dominant dystrophic epidermolysis bullosa, by COL7A1 molecular analysis

We report the first direct molecular prenatal diagnosis, undertaken for the autosomal dominant form of dystrophic epidermolysis bullosa (DDEB). The proband had a moderately severe form of DDEB, with episodic blistering of skin and mucosal involvement. Diagnostic histopathological examination, using electron microscopy to evaluate skin from a fresh blister, demonstrated a zone of cleavage beneath the epidermal-dermal junction, thereby assigning the EB as dystrophic. DNA analysis of COL7A1, the gene encoding type VII collagen, identified a heterozygous transversion (G to A) in the triple helix domain (G2043R). For any subsequent pregnancy, the affected mother and the unaffected father of the proband requested prenatal prediction, which was thereafter carried out in DNA extracted from a chorionic villus sample obtained at 11 weeks of gestation. Restriction enzyme analysis of COL7A1 exons 73 and 74 amplified by PCR, demonstrated the presence of the G2043R mutation, and the pregnancy was subsequently terminated. Molecular analysis of DNA extracted from fetal tissues confirmed the prenatal prediction.

Strategy for identification of sequence variants in COL7A1 and a novel 2-bp deletion mutation in recessive dystrophic epidermolysis bullosa

The diagnostic hallmark of the dystrophic forms of epidermolysis bullosa (DEB), a group of heritable blistering skin diseases, is abnormalities in the anchoring fibrils at the dermal-epidermal basement membrane zone. Since type VII collagen is the major, if not the exclusive, component of the anchoring fibrils, the corresponding gene (COL7A1) is the candidate gene in DEB. Recent cloning of the type VII collagen cDNA and elucidation of the exon-intron organization of the gene have provided the basis for us to develop a novel strategy for identification of sequence variants in COL7A1. Optimization of 72 balanced primer pairs corresponding to flanking intronic sequences allowed PCR amplification of all 118 exons directly from genomic DNA. The PCR products were examined by heteroduplex analysis followed by comparative nucleotide sequencing. More than 100 sequence variants have been identified thus far in COL7A1 using this method, some of which are single base pair polymorphisms and many of which are pathogenetic mutations contributing to the blistering phenotype in DEB. The comprehensive method described is useful for rapid, reliable, and sensitive detection of sequence variants in COL7A1. We demonstrate the utility of this novel strategy in mutation detection and prenatal exclusion of RDEB in a consanguineous family at risk for recurrence.

Molecular basis of dystrophic epidermolysis bullosa: mutations in the type VII collagen gene (COL7A1)

Epidermolysis bullosa (EB), a group of heritable blistering diseases characterized by tissue separation within the cutaneous basement membrane zone, is inherited either in an autosomal dominant or autosomal recessive fashion. EB has been divided into four broad categories based on the precise level of tissue separation. In the dystrophic forms of EB (DEB), tissue separation occurs below the lamina densa within the upper papillary dermis at the level of anchoring fibrils, which are frequently altered in morphology, reduced in number, or entirely absent. Since type VII collagen is the major component of anchoring fibrils, the corresponding gene, COL7A1, was proposed as the candidate for DEB. Subsequent cloning of COL7A1 and elucidation of its genomic structure have led to identification of 53 distinct mutations in COL7A1 reported thus far. These mutations consist of nonsense mutations, small insertions or deletions resulting in frameshift and premature termination codons, splice site mutations, or missense mutations, particularly glycine substitutions within the collagenous domain of the protein. The types and combinations of these mutations and their positions along the type VII collagen molecule result in a spectrum of phenotypic severity and determine the mode of inheritance. Thus, examination of the mutation database has allowed genotype/phenotype predictions, with an impact on genetic counseling in this group of genodermatoses.

Neonatal skin disorders: a review of selected dermatologic abnormalities

The skin serves many purposes, acting as a barrier to infection, protecting internal organs, contributing to temperature regulation, storing insulating fats, excreting electrolytes and water, and providing tactile sensory input. This article focuses on a review of normal skin structure and function and selected neonatal skin disorders. The disorders reviewed are Staphylococcal scalded skin syndrome, epidermolysis bullosa, and the ichthyoses. The basis for each skin disorder is presented. Nursing management and skin care are incorporated into the review of each selected disorder.

Mutation analysis and molecular genetics of epidermolysis bullosa

Cutaneous basement membrane zone (BMZ) consists of a number of attachment structures that are critical for stable association of the epidermis to the underlying dermis. These include hemidesmosomes, anchoring filaments and anchoring fibrils which form an interconnecting network extending from the intracellular milieu of basal keratinocytes across the dermal-epidermal basement membrane to the underlying dermis. Aberrations in this network structure, e.g. due to genetic lesions in the corresponding genes, can result in fragility of the skin at the level of the cutaneous BMZ. The prototype of such diseases is epidermolysis bullosa (EB), a heterogeneous group of genodermatoses characterized by fragility and blistering of the skin, often associated with extracutaneous manifestations, and inherited either in an autosomal dominant or autosomal recessive manner. Based on constellations of the phenotypic manifestations, severity of the disease, and the level of tissue separation within the cutaneous BMZ, EB has been divided into clinically distinct subcategories, including the simplex, hemidesmosomal, junctional and dystrophic variants. Elucidation of BMZ gene/protein systems and development of mutation detection strategies have allowed identification of mutations in 10 different BMZ genes which can explain the clinical heterogeneity of EB. These include mutations in the type VII collagen gene (COL7A1) in the dystrophic (severely scarring) forms of EB; mutations in the laminin 5 genes (LAMA3, LAMB3 and LAMC2) in a lethal (Herlitz) variant of junctional EB; aberrations in the type XVII collagen gene (COL17A1) in non-lethal forms of junctional EB; mutations in the alpha6 and beta4 integrin genes in a distinct hemidesmosomal variant of EB with congenital pyloric atresia; and mutations in the plectin gene (PLEC1) in a form of EB associated with late-onset muscular dystrophy. Identification of mutations in these gene/protein systems attests to their critical importance in the overall stability of the cutaneous BMZ. Furthermore, elucidation of mutations in different variants of EB has direct clinical applications in terms of refined classification, improved genetic counseling, and development of DNA-based prenatal testing in families with EB.

Molecular pathology of the cutaneous basement membrane zone

Recent research has provided considerable information concerning the biology of the cutaneous basement membrane zone (BMZ) in health and disease. In particular, identification of pathogenetic mutations in the genes encoding protein components at the BMZ has done much to increase our understanding of the inherited skin blistering disease, epidermolysis bullosa (EB). As the molecular pathology of different forms of EB is elucidated, correlations between genotype and phenotype become apparent. Determination of specific mutations in patients and families has not only clinical significance, but has also led to the introduction of DNA-based prenatal testing for severe forms of disease, and has laid the foundations for the development of future treatments including gene therapy.

Prenatal diagnosis as a test for genodermatoses: its past, present and future

The prenatal diagnosis (PND) of severe hereditary skin diseases started in the early 1980s using fetal skin biopsy techniques based on ultrastructural and immunohistochemical abnormalities of the fetal skin. Recent success in identifying responsible genes and demonstrating mutations in such genes has set the stage for DNA-based PND in the 1990s. Common examples of skin conditions which can be prenatally diagnosed include epidermolysis bullosa, oculocutaneous albinism and Harlequin ichthyosis in which the severity of the clinical phenotype appears to justify PND in families at risk. More recently, preimplantation diagnoses of inherited diseases have become possible using in vitro fertilization techniques. The diagnosis consists of a blastomere biopsy of the six to ten-cell embryo and a DNA analysis of single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus found to be affected by conventional PND. Furthermore, carrying out a PND using a single fetal cell from the maternal blood, such as nucleated erythrocytes, has become technically feasible. Although there are many questions that remain unanswered, the outlook for further development of noninvasive PND in the future appears optimistic.

Informativeness of polymorphic markers for prenatal diagnosis of recessive dystrophic epidermolysis bullosa in Spanish families at risk

DNA polymorphic markers are useful for the prenatal diagnosis of generalized recessive dystrophic epidermolysis bullosa (GRDEB) in families with at least one child affected with the disease. It is our policy to investigate families at risk using DNA polymorphic markers before a new pregnancy is intended, to inform about the real chances of offering an accurate prenatal diagnosis based on such DNA markers. We have analysed 10 Spanish families with at least one child affected with GRDEB with three different markers linked to the type VII collagen gene: the intragenic PvuII RFLP, and two markers mapped close to the COL7A1 gene, an MspI polymorphism belonging to the anonymous marker D3S2, and the microsatellite D3S1100. The PvuII marker was partially informative in two of 10 families, and was fully informative in three additional families; The MspI marker was partially informative in two of 10 families, and was fully informative in three additional families; it was not informative in five families. The D3S1100 microsatellite was partially informative in two out of 10 families, and fully informative in the other eight families. Combination of all three markers was shown to be partially informative in one family and fully informative in the remaining nine families. Using this combination of markers, we have inferred an accurate linkage-based prenatal diagnosis of GRDEB in four pregnancies. Surprisingly, the intragenic marker PvuII had a very limited usefulness, despite the results of previous studies; the microsatellite D3S1100 offered the best results for an eventual prenatal diagnosis of GRDEB. However, families at risk should be informed that extragenic markers may fail due to the possibility of recombination, estimated as 5% for D3S1100.

Frameshift mutations in the type VII collagen gene (COL7A1) in five Mexican cousins with recessive dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the type VII collagen gene (COL7A1). In this study, we assessed the molecular basis of recessive DEB in five affected individuals from two Mexican families. Both fathers of the affected children were first cousins. Genomic DNA was extracted from peripheral blood samples and assessed for COL7A1 mutations by polymerase chain reaction (PCR) amplification, heteroduplex analysis and direct automated sequencing of PCR products displaying heteroduplex bandshifts. In one family, we identified a homozygous 1 bp insertion of a G nucleotide in exon 19 of COL7A1, designated 2470insG, in three affected sisters. This mutation causes a frameshift and a premature termination codon on both alleles 178 bp downstream from the insertion; both parents were shown to be heterozygous carriers of this mutation. In the second family, the father of the other two affected children was also found to be a heterozygous carrier of this frameshift mutation. In addition, his unrelated partner was shown to be a heterozygous carrier of a different COL7A1 frameshift mutation, an insertion of a T nucleotide in exon 32, designated 3948insT. This mutation also results in a premature termination codon, 126 bp downstream from the insertion. Both affected children were compound heterozygotes for the 2470insG/3948insT mutations in COL7A1. Overall, these molecular findings offer a genetic explanation for the skin fragility in these related Mexican patients with recessive DEB. Immediate benefits from elucidation of the mutations include assessment of carrier status in other members of the family and the feasibility of DNA-based prenatal testing in subsequent pregnancies.

Preimplantation genetic diagnosis of severe inherited skin diseases

Considerable progress has been made recently in elucidating the molecular pathology underlying several forms of inherited skin diseases. One of the most immediate benefits of these discoveries has been the development of DNA-based prenatal diagnosis in pregnancies at risk for recurrence of a particular disorder. In less than 2 decades, prenatal testing has progressed from mid-trimester fetal skin biopsies or protein analysis in a limited number of conditions to first trimester chorionic villus sampling in a much broader range of genodermatoses. Advances in in vitro fertilization protocols and embryo manipulation technology have further led to the feasibility of even earlier prenatal diagnosis through preimplantation genetic diagnosis. This article details some of the recent advances in genetic skin disease research relevant to prenatal diagnosis and explores the possibilities and practicalities of preimplantation genetic diagnosis in the prevention of these conditions.

Dohi memorial lecture. Clinical implications of basic research on heritable skin diseases

Spectacular success has recently been made in understanding the molecular basis of various heritable skin diseases. A prototype of such conditions is epidermolysis bullosa (EB), a heterogenous group of mechano-bullous disorders, characterized by fragility of the skin and other specialized epithelia. The fragility of the skin in EB results from defective attachment of the epidermis to the underlying dermis due to genetic lesions within molecules of the basement membrane zone (BMZ) at the dermal-epidermal junction. Specifically, distinct mutations have been disclosed thus far in ten different genes encoding the macromolecular components of the BMZ, and the combinations and the types of mutations as well as their positions along the altered gene products collectively reflect the phenotypic variability observed in this group of heritable skin diseases. This information has major implications for genetic counseling of families at risk for recurrence of EB in subsequent pregnancies and in future generations. Furthermore, examination of specific mutations in an affected newborn allows prognostication of the severity of the clinical outcome. Finally, mutation analyses have provided the basis to develop DNA-based prenatal testing by chorionic villus sampling or early aminocentesis during the first trimester of gestation. Collectively, the advances on EB exemplify the potential of molecular biology for improved diagnosis and patient care of genetic skin disorders.

Recurrent mutations in the type VII collagen gene (COL7A1) in patients with recessive dystrophic epidermolysis bullosa

Mutations in the type VII collagen gene (COL7A1) are known to underlie different forms of the inherited blistering skin disease dystrophic epidermolysis bullosa (DEB). Most COL7A1 mutations are unique to individual families, and therefore it is usually necessary to screen all 118 exons of the gene to determine the molecular pathology in a patient with DEB. This study aimed to identify any recurrent mutations in COL7A1 that might be applicable to mutation-detection strategies in these patients. Mutational analysis was undertaken in 23 British patients with autosomal recessive DEB using PCR amplification of genomic DNA followed by heteroduplex analysis, nucleotide sequencing, and restriction site analysis. Two recurrent mutations were identified: R578X (6 of 46 alleles) and 7786delG (7 of 46 alleles). Haplotype analysis revealed that the mutations existed on similar allelic backgrounds in different patients, consistent with propagation of common British ancestral haplotypes, although R578X and 7786delG also have been described in DEB patients from other ethnic backgrounds. Given the high relative frequency of these two COL7A1 mutations, British patients with recessive DEB should be screened initially for these nucleotide changes by PCR amplification of genomic DNA and restriction analysis before more exhaustive screening of COL7A1.

Phenytoin reduces the contraction of recessive dystrophic epidermolysis bullosa fibroblast populated collagen gels

Recessive dystrophic epidermolysis bullosa (RDEB) is a group of genetic disorders in which blistering occurs below the basement membrane, in many cases resulting in extensive scar formation, contractures and mitten deformities. Our aim was to compare quantitatively the contraction forces generated by normal and RDEB fibroblats and to investigate the effect of Phenytoin (5,5-diphenyl-2,4-imidazolidinedione, sodium salt; PHT). PHT is an anticonvulsant agent, that causes fibrosis as a side effect. This study utilised conventional untethered fibroblast populated collagen lattice contraction and a quantitative force measurement instrument, the culture force monitor (CFM). The RDEB cell lines were hypercontractile, generating 2.5 times the force of normal fibroblasts, though they appeared morphologically normal. In untethered collagen gels PHT (20 micrograms/ml) significantly reduced contraction of both normal and RDEB fibroblasts over 7 days. Pre-treatment of RDEB cells for 5 days also produced a 40% reduction in contraction as measured in the CFM. One suggested mechanism of PHT action is through inhibition of matrix metalloproteinase activity, but the similar effects of PHT and Colchicine (an inhibitor of microtubule polymerisation) in the CFM, indicate that it may act on contraction through disruption of microfilaments and changes to cell shape. These findings show that isolated RDEB fibroblasts retain the hypercontractile features of many of the patient's lesion sites and imply that local application of PHT may have a therapeutic effect in controlling contraction.

Ultrastructural differentiation of epidermolysis bullosa subtypes and porphyria cutanea tarda

Identifying subtypes of epidermolysis bullosa clinically, particularly at the time of disease onset, can be extremely difficult. In this investigation samples of intact skin from cases of epidermolysis bullosa and porphyria cutanea tarda were examined ultrastructurally and compared with normal tissue. The histological composition of the blister roof and floor surfaces was also evaluated. Three of the ten epidermolysis bullosa subtypes examined revealed specific features. Distinctive, circumscribed, clumped tonofilament bodies were present in basal keratinocytes from epidermolysis bullosa herpetiformis Dowling-Meara. Blister formation in epidermolysis bullosa simplex generalisata gravis occurred immediately above the dermo-epidermal junction aspect of stratum basale cells and thick (30 nm diameter), cross-striated anchoring fibrils were absent in epidermolysis bullosa dystrophica generalisata gravis. Features relating to the lamina densa of the dermo-epidermal junction, dermal capillaries and blister composition were distinctive, but not confined to a particular epidermolysis bullosa subtype or porphyria cutanea tarda.

First trimester DNA-based exclusion of recessive dystrophic epidermolysis bullosa from chorionic villus sampling

A 28-year-old woman, who previously had had a child affected with the hereditary blistering skin disorder, recessive dystrophic epidermolysis bullosa, presented at 7 weeks' gestation for prenatal diagnosis. Genomic DNA, obtained from her, her husband (who is a first cousin), their unaffected child, and their previously affected child, was used to screen all 118 exons of the type VII collagen gene (COL7A1) by polymerase chain reaction (PCR) amplification followed by heteroduplex analysis of the PCR products. Established common polymorphisms within the NC-1 region of COL7A1 were informative for both the normal maternal and paternal alleles. In addition, a putative homozygous mutation, a G to C transversion at nucleotide position 7708, was identified in the affected child. This substitution converts a glycine residue (GGT) within the Gly-X-Y region of the type VII collagen triple helix into an arginine residue (CGT), and leads to the creation of a new MnlI restriction site. Both parents and the healthy sibling were shown to be clinically normal heterozygous carriers of this mutation. A chorionic villus biopsy was performed at 10 weeks' gestation and DNA was extracted from the villi. Assessment of informative intragenic markers, and the putative mutation, revealed that the fetus had inherited both the normal maternal and paternal COL7A1 alleles. Thus, first trimester DNA-based prenatal diagnosis predicts that this child is neither affected with recessive dystrophic epidermolysis bullosa, nor is an unaffected carrier of this genodermatosis.

Management of patients with epidermolysis bullosa

Epidermolysis bullosa is a group of systemic disorders whose management requires familiarity with its many extracutaneous complications. These include gastrointestinal, ophthalmologic, laryngeal, dental, and hematologic problems. This article reviews wound care and management of systemic complications seen in patients with epidermolysis bullosa.

Molecular complexity of the cutaneous basement membrane zone. Revelations from the paradigms of epidermolysis bullosa

Spectacular success has recently been made towards elucidation of the molecular basis of various forms of epidermolysis bullosa (EB), a group of heritable blistering skin diseases. The information derived from these studies has already had a profound impact in terms of precise diagnosis and classification, early prenatal prediction of the phenotype and genetic counseling in families at risk for recurrence. This review highlights recent progress made in defining the molecular basis of junctional and dystrophic forms of EB and the genotype/phenotype relationships established from these studies. Extensive molecular studies, such as the ones captured in this review, form a foundation for the rational design of gene therapies to counteract these conditions in the future.

Molecular basis of recessive dystrophic epidermolysis bullosa: genotype/phenotype correlation in a case of moderate clinical severity

Mutations within the gene encoding the anchoring fibril protein type VII collagen (COL7A1) have recently been established as the pathogenetic basis for the inherited blistering skin disorder, dystrophic epidermolysis bullosa. We report a patient with a moderately severe phenotype of recessive dystrophic epidermolysis bullosa. We report a patient with a moderately severe phenotype of recessive dystrophic epidermolysis bullosa, in whom COL7A1 mutations have been identified on both alleles. The patient is a 5-y-old Japanese male of nonconsanguineous parents, with clinical features including generalized trauma-induced blistering since birth, complete loss of nails, and partial fusion of the fingers and toes. Immunofluorescence microscopy examination of the dermal-epidermal junction in the patient's skin revealed near-normal intensity staining with an antitype VII collagen antibody (LH7:2). Transmission electron microscopy showed a reduced number of thin, poorly-formed anchoring fibrils. PCR amplification of genomic DNA, followed by heteroduplex analysis, and nucleotide sequencing demonstrated that the patient was a compound heterozygote for a nonsense mutation (E2858X) within the NC-2 domain of type VII collagen and a missense mutation (G2576R) within the type VII collagen triple helix. Both mutations were verified by restriction endonuclease digestion. Information about these mutations advances our understanding of genotype-phenotype correlations in dystrophic epidermolysis bullosa, and further delineates the mechanisms involved in dermal-epidermal dysadhesion.

Use of type VII collagen gene (COL7A1) markers in prenatal diagnosis of recessive dystrophic epidermolysis bullosa

Generalised recessive dystrophic epidermolysis bullosa (EB) is a severe inherited disease in which patients suffer from blistering and scarring of the skin and mucous membranes after minor mechanical trauma. Tight genetic linkage has been established to the type VII collagen gene (COL7A1) at 3p21, with no evidence of locus heterogeneity. Several COL7A1 mutations have now been identified in recessive dystrophic EB patients. Prenatal diagnosis has been performed by examination of a fetal skin biopsy taken at about 16 weeks' gestation, and relies on identification of characteristic ultrastructural and immunohistochemical changes. We have now achieved a first trimester prenatal diagnosis using intragenic and flanking COL7A1 markers in a pregnancy at risk for recessive dystrophic EB. Segregation of the informative markers predicted the baby would be an unaffected carrier. The pregnancy continued to term and a healthy baby was born, confirming this result.