Compound heterozygosity for novel splice site mutations in the BPAG2/COL17A1 gene underlies generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa, GABEB (OMIM# 226650), is a nonlethal variant of epidermolysis bullosa with autosomal recessive inheritance pattern. The pathogenesis of this disorder can be caused by mutations affecting two different gene/protein systems. Most of the mutations have been identified in the BPAG2/COL17A1 gene encoding a hemidesmosomal transmembrane protein, the 180 kDa bullous pemphigoid antigen (BP180), also known as type XVII collagen. The minority of the mutations are localized in the LAMB3 gene encoding the beta3 polypeptide of laminin 5. In In this study we describe a GABEB patient who showed absent expression of BP180 in the cultured keratinocytes as well as in the skin. The patient was a compound heterozygote for two different splice site mutations, 3053-1G-->C and 3871+1G-->C, affecting the extra-cellular domain of the protein. These mutations resulted in multiple aberrant splice variants, three of them causing premature termination codons for translation. This case, dealing with out-of-frame splice site mutations in BPAG2/COL17A1, attests to the molecular heterogeneity of GABEB.

The role of parents' self-esteem, mastery-orientation and social background in their parenting styles

In order to examine the extent to which parents' levels of education, financial resources, self-esteem, and their mastery-orientation versus task-avoidance are associated with their parenting styles and parental stress, data from two studies were analyzed. In Study I, parents of 105 6 to 7-year old children were asked to fill in scales measuring their parenting styles and parental stress, mastery-orientation, financial resources, and their level of education. In Study II, 235 parents were asked to fill in the same scales. An identical pattern of results was found in the two studies. Parents' self-esteem and their use of mastery-oriented strategy were found to be associated with authoritative parenting and low parental stress, whereas parents' low level of education was related to an authoritarian parenting style. The results further showed that the impact of parents' self-esteem on authoritative parenting and parental stress was partly mediated by their use of a mastery-oriented strategy.

Expression of plectin and HD1 epitopes in patients with epidermolysis bullosa simplex associated with muscular dystrophy

Plectin, a widespread cytoskeletal linker protein, is prominently expressed in basal keratinocytes of the epidermis. HD1, originally identified as a hemidesmosomal protein, has been suggested to be an isoform of or closely related to plectin, but the exact relationship between these proteins is unknown. Plectin has recently been identified as the gene/protein system at fault in epidermolysis bullosa simplex associated with muscular dystrophy (EBS-MD; OMIM# 226670). In this study, we examined the expression patterns of plectin and HD1 epitopes in the skin of four unrelated patients with EBS-MD confirmed to be caused by plectin gene mutations. By indirect immunofluorescence, all monoclonal antibodies (mAbs) to plectin (5B3, 10F6) or to HD1 (121, E2, K15, 156) bound to the epidermal basement membrane zone (BMZ) of normal human skin. In addition, immunostaining along the periphery of keratinocytes was detected with mAbs 5B3, 10F6 (antiplectin), K15 and 156 (anti-HD1), but not with mAbs 121 and E2 (anti-HD1). Immunolabeling for mAbs 5B3 and 10F6 (antiplectin) was absent in the skin of three patients who had premature termination codon mutations in the plectin gene in both alleles. In contrast, labeling was only slightly reduced in a patient who was homozygous for a 9-bp in-frame deletion mutation in the same gene. Interestingly, peripheral labeling of keratinocytes using mAbs K15 and 156 (anti-HD1) was clearly present in all the patients despite the disappearance of BMZ labeling. Quantitative analysis by postembedding immunoelectron microscopy demonstrated that both plectin and HD1 epitopes were localized in the inner plaque of hemidesmosomes with a mean distance of 110 and 120 nm from the plasma membrane, respectively. These results confirm the molecular heterogeneity of EBS-MD in terms of the expression patterns of plectin and HD1 epitopes which correlate with clinical severity, the pattern of plectin gene mutations and their consequences.

Splicing modulation of integrin beta4 pre-mRNA carrying a branch point mutation underlies epidermolysis bullosa with pyloric atresia undergoing spontaneous amelioration with ageing

A general improvement with ageing has been reported in a few cases of epidermolysis bullosa with pyloric atresia (PA-JEB), an autosomal recessive skin disease characterized by extensive disadhesion of epithelia. In a patient who improved from severe to mild PA-JEB, a search for mutations in the integrin beta4 gene (IGTB4) detected heterozygosity for a novel base substitution 3986-19T-->A in the putative branchpoint sequence of intron 31, and a point mutation 3802+1G-->A in the donor splice site of intron 30 previously associated with severe PA-JEB. Analysis of mRNA showed that the intronic mutation prevents legitimate splicing of the beta4 pre-mRNA. Functional splicing can be restored in vitro by seeding the proband's keratinocytes on feeders of irradiated fibroblasts. Study of mRNA in wild-type keratinocytes transfected with IGTB4 minigenes containing intron 31 with or without mutation 3986-19T-->A, confirmed the causative role of the intronic mutation in PA-JEB, and highlighted the influence of feeders on the maturation process of the mutated beta4 pre-mRNA. Our results show that in a context of overall reduction of the beta4 mRNA levels, activation of the legitimate splice site in the aberrant beta4 pre-mRNA underlies the transient severity of the condition. The results also point to the relevance which the interaction between epithelial and stromal cells may have in modulating expression of integrin receptors.

Dominant dystrophic epidermolysis bullosa (Pasini) caused by a novel glycine substitution mutation in the type VII collagen gene (COL7A1)

A 12 y old girl with the albopapuloid variant (Pasini) of dominant dystrophic epidermolysis bullosa is studied. The albopapuloid lesions developed within the first year of life, contained milia and were associated with pruritus. Mutation detection of the COL7A1 gene revealed a G-->A transition at nucleotide position 6110 in the mutant allele converting a glycine to glutamic acid (G2037E). This report adds to the expanding database on COL7A1 mutations in dystrophic epidermolysis bullosa.

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.

[Prenatal diagnosis of recessive hereditary dystrophic epidermolysis bullosa with haplotype analysis of the type VII collagen gene]

DNA-based prenatal testing of the fetal genotype was performed in a family at risk for recurrence of recessive dystrophic epidermolysis bullosa (RDEB). DNA from cultured fibroblasts and leukocytes from the peripheral blood of the previously affected offspring, DNA from parental leukocytes and DNA from fetal tissue obtained by chorionic villus biopsy was analysed by direct PCR amplification of known polymorphic regions within or flanking the type VII collagen gene, the candidate gene in RDEB. One flanking marker (D3S2/Mspl) as well as two intragenic polymorphisms (C7/Mspl, C7/Eco01091) in exons 30 and 84 were informative in this family. Thus, based on the haplotype analysis and the lack of evidence for locus heterogeneity in RDEB, a phenotypically healthy child was predicted. This prediction was confirmed by the birth of a healthy female infant. The study reports successful determination of the fetal genotype by PCR-based prenatal diagnosis in a family at risk for recurrence of severe RDEB.

Four novel plectin gene mutations in Japanese patients with epidermolysis bullosa with muscular dystrophy disclosed by heteroduplex scanning and protein truncation tests

Epidermolysis bullosa with muscular dystrophy (EB-MD) is a distinct variant of EB caused by mutations in the plectin gene (PLEC1). In this study, we have examined two Japanese patients with EB-MD using heteroduplex scanning or a protein truncation test for mutation detection analysis. The results revealed that both patients were compound heterozygotes for novel PLEC1 mutations (Q1936X/Q1053X and R2421X/12633ins4), which all caused premature termination of translation of the corresponding polypeptides. These cases, which demonstrate the utility of two complementary mutation detection strategies, add to the repertoire of plectin mutations in EB-MD.

Novel and de novo glycine substitution mutations in the type VII collagen gene (COL7A1) in dystrophic epidermolysis bullosa: implications for genetic counseling

The dystrophic forms of epidermolysis bullosa (DEB) are due to mutations in the type VII collagen gene (COL7A1). In dominant DEB, a characteristic genetic lesion is a glycine substitution mutation within the collagenous domain of the protein. In this study, we have examined the molecular basis of six new families in which the proband has clinical features and/or ultrastructural findings consistent with DEB. The results revealed a glycine substitution mutation in all six families, four of which are novel and previously unpublished. In three families with clinically unaffected parents, de novo mutations G2043R and G2040V were found. These results emphasize the predominance of glycine substitution mutations in dominant DEB, and indicate that in some cases the phenotype is due to de novo dominant mutations.

The 97 kDa linear IgA bullous dermatosis antigen is not expressed in a patient with generalized atrophic benign epidermolysis bullosa with a novel homozygous G258X mutation in COL17A1

The nature and expression pattern of the 97 kDa linear IgA bullous dermatosis antigen (LAD-1) and its role in epidermolysis bullosa have not been fully elucidated. In this study, we examined the expression of LAD-1 in the skin specimens of 70 patients with the various subtypes of epidermolysis bullosa, including simplex (n = 23), junctional (n = 15), and dystrophic variants (n = 32). For immunolabeling, we used two recently developed monoclonal antibodies to LAD-1 whose epitopes were ultrastructurally localized in the lamina lucida between NC16A and carboxyterminal domains of BPAG2, as well as autoantibodies against LAD-1 from the sera of two patients with linear IgA dermatosis. Among the 70 patients, only one patient with generalized atrophic benign epidermolysis bullosa failed to demonstrate LAD-1 expression. Although other major basement membrane components, including laminin 5, BPAG1, plectin, alpha6 and beta4 integrins, as well as type IV and type VII collagens were normally expressed, BPAG2/type XVII collagen was absent from the skin of this patient. Mutation analysis on COL17A1 using polymerase chain reaction amplification, heteroduplex scanning, and direct nucleotide sequencing revealed that this patient was homozygous for a novel nonsense mutation G258X in exon 11, and her parents were heterozygous carriers for this mutation. This is the first mutation located in the intracellular domain of BPAG2, and resides 817 bp upstream from the N-terminal amino acid sequence of LAD-1. These findings indicate that the absent expression of LAD-1 is observed in a BPAG2-deficient generalized atrophic benign epidermolysis bullosa patient with mutations in both alleles of COL17A1, and not in other epidermolysis bullosa subtypes. These findings also support the notion that LAD-1 is a degradation product of BPAG2.

Pyloric atresia-junctional epidermolysis bullosa syndrome: mutations in the integrin beta4 gene (ITGB4) in two unrelated patients with mild disease

Junctional epidermolysis bullosa associated with pyloric atresia (EB-PA; OMIM 226730) is a rare autosomal recessively inherited disease in which mucocutaneous fragility is associated with gastrointestinal atresia. This disease is usually fatal within the first few weeks or months of life even following surgical correction of the intestinal obstruction. Recently, mutations in the genes encoding the epithelial integrin alpha6beta4 (ITGA6 and ITGB4) have been identified in several patients with EB-PA. We report two unrelated patients with this disease who have survived into early childhood with mild cutaneous involvement, in whom we have identified pathogenetic mutations in ITGB4. The first patient was a compound heterozygote for a splice site mutation in exon 30 (3793 + 1G-to-A) and a non-sense mutation in exon 36 (W1478X), and the second was a compound heterozygote for a missense mutation in exon 3 (C38R) and a 1 bp deletion in exon 36 (4776delG). Although the non-sense and deletion mutations are predicted to result in markedly reduced beta4 integrin mRNA levels, the presence of the missense or splice site mutation on the second allele may enable the synthesis of some functional, albeit perturbed, beta4 polypeptide. Determination of the molecular mechanisms in these two cases increases our understanding of EB-PA and may enable correlation between genotype and phenotype.

Novel ITGB4 mutations in lethal and nonlethal variants of epidermolysis bullosa with pyloric atresia: missense versus nonsense

Epidermolysis bullosa with pyloric atresia (EB-PA), an autosomal recessive genodermatosis, manifests with neonatal cutaneous blistering associated with congenital pyloric atresia. The disease is frequently lethal, but nonlethal cases have also been reported. Expression of the alpha6 beta4 integrin is altered at the dermal-epidermal basement-membrane zone; recently, mutations in the corresponding genes (ITGA6 and ITGB4) have been disclosed in a limited number of patients, premature termination codons in both alleles being characteristic of lethal variants. In this study, we have examined the molecular basis of EB-PA in five families, two of them with lethal and three of them with nonlethal variants of the disease. Mutation analysis disclosed novel lesions in both ITGB4 alleles of each proband. One of the patients with lethal EB-PA was a compound heterozygote for premature termination-codon mutations (C738X/4791delCA), whereas the other patient with a lethal variant was homozygous for a missense mutation involving a cysteine residue (C61Y). The three nonlethal cases had missense mutations in both alleles (C562R/C562R, R1281W/R252C, and R1281W/R1281W). Immunofluorescence staining of skin in two of the nonlethal patients and in one of the lethal cases was positive, yet attenuated, for alpha6 and beta4 integrins. These results confirm that ITGB4 mutations underlie EB-PA and show that missense mutations may lead to nonlethal phenotypes.

Novel COL7A1 mutations in dystrophic forms of epidermolysis bullosa

Mutations in the type VII collagen gene (COL7A1) have been shown to underlie different variants of dystrophic epidermolysis bullosa (DEB). Examination of the genetic database indicates that most of the mutations are family specific, with few recurrent mutations. To facilitate further refinement of genotype/phenotype correlations in DEB, we have examined a cohort of nine families with DEB (seven recessively and two dominantly inherited) by a mutation detection strategy based on polymerase chain reaction amplification of COL7A1 genomic sequences, followed by heteroduplex scanning and direct nucleotide sequencing. The results revealed 16 allelic mutations, 11 of them being novel, previously unpublished. The genetic information was also used for prenatal testing in a family at risk for recurrence of a severe, Hallopeau-Siemens type of RDEB. These data contribute to the expanding database of COL7A1 mutations in DEB.

Molecular analysis of the human laminin alpha3a chain gene (LAMA3a): a strategy for mutation identification and DNA-based prenatal diagnosis in Herlitz junctional epidermolysis bullosa

Mutations in the genes (LAMA3, LAMB3, and LAMC2) encoding the subunit polypeptides of the cutaneous basement membrane zone protein laminin 5 have been reported in different forms of junctional epidermolysis bullosa (JEB), an inherited blistering skin disease. In this study, we present the complete exon-intron organization of the "a" transcript of the laminin alpha3 chain gene, LAMA3a, which is expressed primarily in the skin. We have performed fine-resolution mapping of this gene on chromosome 18q11.2 using a human-hamster radiation hybrid panel. We have also developed a mutation-detection strategy based on the exon-intron structure of LAMA3a. This strategy, based on PCR amplification of genomic sequences, followed by heteroduplex scanning and automated nucleotide sequencing, was used for successful mutation screening in a family with the lethal (Herlitz) type of JEB, and two novel LAMA3 mutations were identified in the proband. The mutations consisted of a single-base pair deletion in LAMA3a exon A11 on the paternal allele, designated 1239delC, and a two-base pair deletion in LAMA3a exon A23 on the maternal allele, designated 2959delGG. This information was also used for DNA-based prenatal testing in a subsequent pregnancy in this family. Collectively, these results attest to our expanding capability to elucidate the genetic basis of various forms of epidermolysis bullosa using molecular techniques.

LAMB3 mutations in generalized atrophic benign epidermolysis bullosa: consequences at the mRNA and protein levels

Generalized atrophic benign epidermolysis bullosa (GABEB; OMIM no. 226650) is a rare hemidesmosomal variant of EB, inherited in an autosomal recessive fashion. In previous studies, mutations in the gene (COL17A1) encoding the type XVII collagen, a transmembrane component of hemidesmosomes, were detected in most patients with GABEB. However, evidence for genetic defects in the laminin 5 genes has also been presented. In the present investigation, we examined three patients, representing two families with GABEB, for mutations in the LAMB3 gene. Heteroduplex scanning of the gene, followed by direct automated sequencing, revealed that Patient 1 was a compound heterozygote for a missense mutation (C293S) and a premature termination codon-causing mutation (1367delAC). The latter mutation resulted in accelerated mRNA decay, which rendered the corresponding mRNA transcript undetectable by reverse transcriptase-PCR. Patients 2 and 3, siblings with slightly different clinical presentations, were homozygous for a G-->A transition affecting the last nucleotide of exon 7 (628G-->A). This mutation resulted in amino acid substitution (E210K), as well as in multiple aberrant splice variants affecting exons 6 to 8. These observations expand the repertoire of LAMB3 mutations in nonlethal variants of EB, and they illustrate the consequences of the mutations at the mRNA and protein levels.

Tibial muscular dystrophy--from clinical description to linkage on chromosome 2q31

A genome scan with highly polymorphic markers has established linkage for tibial muscular dystrophy (TMD), a recently described late onset distal myopathy, to a novel myopathy locus on chromosome 2q31. The mode of inheritance in TMD is autosomal dominant and the typical symptom of ankle dorsiflexion weakness appears in the fourth to seventh decade. Weakness of lower leg muscles is slowly progressive eventually causing a moderate foot drop. Overall disability usually remains mild even in elderly patients and walking ability is preserved throughout the patient's lifetime. The main target of the disease, the tibial anterior muscle, shows progressive dystrophic changes with rimmed vacuoles at the early stages and complete replacement pathology at later stages of the disease. The linkage studies in four different TMD families revealed a common core haplotype with a set of markers on the chromosome 2q31 locus. This indicates one major ancient founder mutation for TMD in Finland. There is one superior candidate gene on the 2q31 locus, the gene encoding a giant protein titin, expressed in heart and skeletal muscle.

Maternal uniparental meroisodisomy in the LAMB3 region of chromosome 1 results in lethal junctional epidermolysis bullosa

Herlitz junctional epidermolysis bullosa (OMIM#226700) is a lethal, autosomal recessive blistering disorder caused by mutations in one of the three genes LAMA3, LAMB3, or LAMC2, encoding the constitutive polypeptide subunits of laminin 5. In this study, we describe a patient homozygous for a novel nonsense mutation Q936X in exon 19 of LAMB3, which has been mapped to chromosome 1q32. The patient was born with extensive blistering and demonstrated negative immunofluorescence staining for laminin 5, and transmission electron microscopy revealed tissue separation within lamina lucida of the dermal-epidermal junction, diagnostic of Herlitz junctional epidermolysis bullosa. The mother of the proband was found to be a heterozygous carrier for this mutation, whereas the father demonstrated the wild-type LAMB3 allele only. Nonpaternity was excluded by 13 microsatellite markers in six different chromosomes. Genotype analysis using 28 microsatellite markers spanning chromosome 1 revealed that the patient had maternal primary heterodisomy, as well as meroisodisomy within two regions of chromosome 1, one on 1p and the other one on 1q, the latter region containing the maternal LAMB3 mutation. These results suggest that Herlitz junctional epidermolysis bullosa in this patient developed as a result of reduction to homozygosity of the maternal LAMB3 mutation on chromosome 1q32.

Hemidesmosomal variants of epidermolysis bullosa. Mutations in the alpha6beta4 integrin and the 180-kD bullous pemphigoid antigen/type XVII collagen genes

Epidermolysis bullosa (EB), a heterogeneous group of genodermatoses, is characterized by fragility and blistering of the skin, associated with characteristic extracutaneous manifestations. Based on clinical severity, constellation of the phenotypic manifestations, and the level of tissue separation within the cutaneous basement membrane zone, EB has been divided into distinct subcategories. Traditionally, these include the simplex, junctional and dystrophic variants of EB. Recent attention has been drawn to variants of EB demonstrating tissue separation at the level of hemidesmosomes, ultrastructurally recognizable adhesion complexes within the cutaneous basement membrane zone. Clinically, these hemidesmosomal variants manifest either as generalized atrophic benign epidermolysis bullosa (GABEB), EB with pyloric atresia, or EB with late-onset muscular dystrophy. Elucidation of basement membrane zone components by molecular cloning and development of mutation detection strategies have revealed that the hemidesmosomal variants of EB result from mutations in the genes encoding the subunit polypeptides of the 180-kD bullous pemphigoid antigen/type XVII collagen, the alpha6beta4 integrin, or plectin, respectively. Collectively, these data add to the understanding of the molecular complexity of the cutaneous basement membrane zone in EB, as attested by the fact that mutations in 10 different genes can underlie different variants of EB. Elucidation of mutations in different forms of EB has direct application to genetic counseling and DNA-based prenatal testing in families with EB.

Compound heterozygosity for missense (L156P) and nonsense (R554X) mutations in the beta4 integrin gene (ITGB4) underlies mild, nonlethal phenotype of epidermolysis bullosa with pyloric atresia

Mutations in the genes encoding the subunit polypeptides of the alpha6beta4 integrin (ITGA6 and ITGB4, respectively) have been previously demonstrated in patients with a lethal form of epidermolysis bullosa with congenital pyloric atresia (OMIM #226730). In this study, we demonstrate for the first time ITGB4 mutations in nonlethal phenotype of epidermolysis bullosa with congenital pyloric atresia. Specifically, the proband was shown to be a compound heterozygote for a missense mutation (L156P) and a nonsense mutation (R554X). The leucine substitution by proline was shown to affect a residue, which was precisely conserved in different human, rodent, and drosophila integrin-beta polypeptides, and consequently disrupts the alpha-helix formation of the polypeptide segment as determined by Garnier alpha-helicity plot. The nonsense mutation in another allele was accompanied by undetectable levels of the corresponding mRNA transcript, as determined by reverse transcription-polymerase chain reaction. The presence of a missense mutation, when combined with a premature termination codon mutation, may explain the milder blistering tendency of the skin in this patient.