Generalized Atrophic Benign Epidermolysis Bullosa Research Articles

Targeted Gene Addition in Human Epithelial Stem Cells by Zinc-finger Nuclease-mediated Homologous Recombination

Preclinical and clinical studies showed that autologous transplantation of epidermis derived from genetically modified epithelial stem cells (EpSCs) leads to long-term correction of inherited skin adhesion defects. These studies were based on potentially genotoxic retroviral vectors. We developed an alternative gene transfer strategy aimed at targeting a "safe harbor" locus, the adeno-associated virus integration site 1 (AAVS1), by zinc-finger nuclease (ZFN)-induced homologous recombination (HR). Delivery of AAVS1-specific ZFNs and a GFP-expressing HR cassette by integration-defective lentiviral (LV) vectors (IDLVs) or adenoviral (Ad) vectors resulted in targeted gene addition with an efficiency of > 20% in a human keratinocyte cell line, > 10% in immortalized keratinocytes, and < 1% in primary keratinocytes. Deep sequencing of the AAVS1 locus showed that ZFN-induced double-strand breaks are mostly repaired by nonhomologous end joining (NHEJ) in primary cells, indicating that poor induction of the HR-dependent DNA repair pathway may be a significant limitation for targeted gene integration. Skin equivalents derived from unselected keratinocyte cultures coinfected with a GFP-IDLV and a ZFN-Ad vector were grafted onto immunodeficient mice. GFP-positive clones were observed in all grafts up to 18 weeks post-transplantation. By histological and molecular analysis, we were able to demonstrate highly efficient targeting of the AAVS1 locus in human repopulating EpSCs.

Eosinophil infiltration in three patients with generalized atrophic benign epidermolysis bullosa from a Japanese family: molecular genetic and immunohistochemical studies

Generalized atrophic benign epidermolysis bullosa (GABEB), a subtype of epidermolysis bullosa (EB), is an autosomal recessive skin disease characterized by derm-epidermal separation leading to skin fragility and atrophy and other associated abnormalities. Although a few reports demonstrated that eosinophils are infiltrating beneath bullas in infants with some types of EB, no such condition in adult GABEB patients has been known. Here we report on three adult patients with GABEB from a Japanese family, whose bullous skin lesions showed massive eosinophil infiltration. One of the three patients showed amyloid deposition at the intestine, kidney, and skin. Linkage analysis revealed that GABEB in the family was linked to COL17A1 with a maximum LOD score of 3.08. Mutation analysis identified in the three patients a homozygous insertional mutation, 209-210insCA, in exon 5 of COL17A1. The expression of mutated COL17A1 was confirmed by semiquantitative RT-PCR, but no signals for truncated COL17A1 protein were detected by the immunohistochemical studies using antibodies against BP180. Furthermore, no autoantibody against the mutant protein was detected by western blot analysis. It is thus less likely that autoantibody and/or a local immune reaction in their skin has a primary role in eosinophil infiltration in these patients.

A novel homozygous point mutation in the COL17A1 gene in a Chinese family with generalized atrophic benign epidermolysis bullosa

We describe a Chinese family with generalized atrophic benign epidermolysis bullosa (GABEB), a non-lethal variant of junctional epidermolysis bullosa. The proband was an offspring of consanguineous parents, had generalized blisters since birth and developed severe alopecia during early childhood. Ultrastructural examination of the proband's skin revealed fissures in the lamina lucida. Immunofluorescence assays using a monoclonal antibody recognizing the extracellular domain of the 180 kDa bullous pemphigoid antigen (BPAG2) showed loss of fluorescent signal in the basal membrane zone of the skin. DNA sequencing revealed a homozygous C-to-G transversion at nucleotide position 899 in exon 11 of the COL17A1 gene, which encodes BPAG2. This mutation results in serine to cysteine at position 265, which is located in a highly conserved region of the intracellular domain of BPAG2. We showed that the proband's father was heterozygous for this mutation. In addition, we found a novel polymorphic substitution of C-to-G at nucleotide position 798 in exon 10 of the COL17A1 gene, which results in an I233M change in BPAG2 and is a common polymorphic allele in a limited Chinese population.

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.

Role of the Bullous Pemphigoid Antigen 180 (BP180) in the Assembly of Hemidesmosomes and Cell Adhesion—Reexpression of BP180 in Generalized Atrophic Benign Epidermolysis Bullosa Keratinocytes

Bullous pemphigoid antigen 180 (BP180) is a transmembrane component of hemidesmosomes (HD), cell–substrate attachment complexes in stratified and complex epithelia. To determine the role of BP180 in the assembly of HD and cell adhesion, using SV40 virions we have immortalized BP180-deficient keratinocytes derived from a patient with the inherited skin blistering disorder generalized atrophic benign epidermolysis bullosa (GABEB). The GABEB keratinocytes form HD-like structures, which contain α6β4 integrin and HD1/plectin, but not the bullous pemphigoid antigen 230 (BP230). The expression of integrin subunits by GABEB keratinocytes was comparable to that of an immortalized normal human keratinocyte cell line (NHK), except for α6 and β4, which were less strongly expressed in GABEB cells. In short-term adhesion assays, both GABEB keratinocytes and NHK bound strongly and to a similar extent to laminin-1, laminin-5, fibronectin, and type IV and V collagens, which suggests that BP180 is not involved in promoting the initial adhesion to these ligands. Transfection of GABEB keratinocytes with cDNAs for wild-type or a mutant of BP180 lacking the collagenous extracellular domain resulted in the expression of recombinant BP180 proteins that were correctly polarized at the basal cell surface together with α6β4. In addition, restored synthesis of BP180 affected the subcellular localization of BP230, which was no longer diffusely distributed in the cytoplasm, but was found in HD-like structures. In contrast, a BP180 mutant with a 36-amino-acid deletion from the amino terminus of the cytoplasmic domain failed to localize to HD-like structures. These results demonstrate that a region within the cytoplasmic domain of BP180 is essential for its localization into HD and that BP180 may play a critical role in coordinating the subcellular distribution of BP230.

LAD-1 Is Absent in a Subset of Junctional Epidermolysis Bullosa Patients

The anchoring filament protein LAD-1 has been recently identified as the target of autoantibodies in the acquired blistering disorder linear IgA bullous dermatosis. Because this protein appears to be involved in the process of dermal-epidermal cohesion, this study sought to determine the involvement of LAD-1 in the pathology of junctional epidermolysis bullosa (JEB). To this end, 44 patients with a variety of subtypes of JEB were analyzed by indirect immunofluorescence microscopy with antibodies to LAD-1, BP180, and laminin-5. We found that only patients with generalized atrophic benign epidermolysis bullosa (GABEB) contained LAD-1 defects. Of the 16 GABEB patients studied, 13 showed absent or greatly reduced expression of LAD-1 (including 2 patients with a peculiar interrupted staining pattern) and 3 patients showed defects of laminin-5 expression with normal LAD-1 expression. Patients who showed LAD-1 defects also showed abnormal expression of BP180. Keratinocytes were cultured from the skin of two GABEB patients and analyzed by indirect immunofluorescent microscopy. One culture demonstrated defects of BP180 and LAD-1 expression (which was also verified by radioimmunoprecipitation assay), and one culture showed decreased laminin-5 expression but normal BP180 and LAD-1 expression. Thus, these studies demonstrate that: (i) LAD-1 and BP180 are normally expressed in all subtypes of JEB except GABEB, (ii) the majority of GABEB patients show absent or near absent expression of both LAD-1 and BP180 but normal expression of laminin-5, and (iii) a smaller subset of GABEB patients show normal LAD-1 and BP180 expression but express persistent but reduced levels of laminin-5.

A Homozygous In-Frame Deletion in the Collagenous Domain of Bullous Pemphigoid Antigen BP180 (Type XVII Collagen) Causes Generalized Atrophic Benign Epidermolysis Bullosa

We report a missplicing event affecting the expression of bullous pemphigoid antigen BP180 (type XVII collagen) in a patient with generalized atrophic benign epidermolysis bullosa (GABEB). The segregation of the mutated allele in the family is consistent with the pathogenic role of the mutation. The homozygous mutation 2441-2A --> G disrupts a splice-site sequence in gene (BPAG2) for BP180 and results in an in-frame exon skipping within the collagenous ectodomain of the protein. The consequent deletion of 9 amino acids in the mutant BP180 is predicted to alter the structure of the homotrimer and is expected to exert a deleterious effect on stability of the protein that would account for the complete absence of immunoreactivity of the proband's skin to antibodies directed against BP180. These findings underscore the importance of structural integrity of the extracellular domain of BP180 for the stability of the protein.

Three Novel Homozygous Point Mutations and a New Polymorphism in the COL17A1 Gene: Relation to Biological and Clinical Phenotypes of Junctional Epidermolysis Bullosa

Junctional epidermolysis bullosa (JEB) is a clinically and biologically heterogeneous genodermatosis, characterized by trauma-induced blistering and healing without scarring but sometimes with skin atrophy. We investigated three unrelated patients with different JEB phenotypes. Patients 1 and 2 had generalized atrophic benign epidermolysis bullosa (GABEB), with features including skin atrophy and alopecia. Patient 3 had the localisata variant of JEB, with predominantly acral blistering and normal hair. All patients carried novel homozygous point mutations (Q1016X, R1226X, and R1303Q) in the COL17A1 gene encoding collagen XVII, a hemidesmosomal transmembrane component; and, therefore, not only GABEB but also the localisata JEB can be a collagen XVII disorder. The nonsense mutations led to drastically reduced collagen XVII mRNA and protein levels. In contrast, the missense mutation allowed expression of abnormal collagen XVII, and epidermal extracts from that patient contained polypeptides of normal size, as well as larger aggregates. The homozygous nonsense mutations in the COL17A1 gene were consistent with the absence of the collagen from the skin and with the GABEB phenotype, whereas homozygosity for the missense mutation resulted in expression of aberrant collagen XVII and, clinically, in localisata JEB.

Mosaic expression of uncein and 180-kDa bullous pemphigoid antigen in generalized atrophic benign epidermolysis bullosa

Immunofluorescence microscopy of epidermodermal junction components in serial cryosections from the perilesional skin of a patient with generalized atrophic benign epidermolysis bullosa (GABEB) showed broken line-like staining of both BPAG2 (180-kDa bullous pemphigoid antigen) and uncein (antigen of 19-DEJ-1 monoclonal antibody), whereas integrin alpha 6 and laminin 5 were continuously expressed along the basement membrane zone. Immunoelectron microscopy revealed a mosaic distribution of the BPAG2/uncein positive and negative cells. BPAG2, a candidate protein of GABEB, probably has a close connection with uncein, and anchoring filament component.

Premature Termination Codons Are Present on Both Alleles of the Bullous Pemphigoid Antigen 2/Type XVII Collagen Gene in Five Austrian Families with Generalized Atrophic Benign Epidermolysis Bullosa

Patients with generalized atrophic benign epidermolysis bullosa (GABEB), an inherited subepidermal blistering disease, often have no immunologically detectable bullous pemphigoid antigen 2 (BPAG2) in their epidermal basement membrane. Recently, we analyzed the BPAG2 gene (GenBank no. M91669) in an Austrian family with GABEB and identified a homozygous deletion mutation, 4003delTC, that results in a downstream premature termination codon (PTC). This mutation has now been identified in additional descendants, suggesting transmission of this mutant allele through at least six generations. Screening of four other Austrian GABEB families revealed that affected members were homozygous for 4003delTC in two cases and heterozygous in two others. In the latter, mutational analysis identified two novel nonsense mutations, Q1403X and G803X, that were confirmed by restriction endonuclease digestions. Thus, PTCs on both alleles of BPAG2 are present in all of these GABEB families. Immunoprecipitation and northern blot studies of cultured keratinocytes from homozygous GABEB patients show that 4003delTC results in undetectable levels of BPAG2 protein and mRNA-findings consistent with the process of nonsense-mediated mRNA decay. Incubating keratinocytes with cycloheximide increased BPAG2 mRNA to a level detectable by northern analysis. When the latter was used in reverse transcription-PCR studies, the mutation was demonstrated, suggesting that cycloheximide may allow mutational analysis in cases where low transcript levels have previously thwarted RT-PCR studies. These findings account for the absence of BPAG2 in GABEB patients and attest to the importance of this protein in adhesion of epidermis to epidermal basement membrane.

Generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa (GABEB) is a rare autosomal recessive variant of junctional epidermolysis bullosa. A typical feature in these patients is the cicatricial alopecia resembling male pattern baldness: in this paper we describe a case of GABEB with particular attention to this characteristic.

Generalized atrophic benign epidermolysis bullosa. Either 180-kd bullous pemphigoid antigen or laminin-5 deficiency.

Generalized atrophic benign epidermolysis bullosa (GABEB) is a form of nonlethal junctional epidermolysis bullosa, clinically characterized by generalized blistering after birth, atrophic healing, and incomplete universal atrophic alopecia with onset in childhood. Recently, we discovered a deficiency of the 180-kd bullous pemphigoid antigen (BP180) and a reduced amount of BP180 messenger RNA in three patients with GABEB. It is not yet clear, however, whether GABEB is invariably caused by BP180 deficiency. We examined 18 patients with nonlethal junctional epidermolysis bullosa from unrelated families; nine of these individuals presented with the clinical characteristics of GABEB. Specimens of clinically normal skin obtained from the patients were stained by immunofluorescence with monoclonal antibodies to BP180 and laminin-5. The BP180 epitopes were not expressed in eight patients, all of whom were sharing the typical clinical features of GABEB. In one of the nine patients with GABEB, the BP180 level was sufficient, but the laminin-5 level was reduced. Among the nine patients with junctional epidermolysis bullosa without atrophic alopecia, laminin-5 level was not expressed in one patient, while in the other patients both antigens were normally expressed. Not all patients with GABEB are deficient in BP180, since some individuals with GABEB only exhibit reduction of the laminin-5 expression. The BP180 deficiency in the skin invariably seems to result in GABEB. Immunofluorescence analysis using monoclonal antibodies against BP180 (and laminin-5) may allow early subtyping, which is of prognostic significance, in children born with junctional epidermolysis bullosa.

Mutations in the 180–kD bullous pemphigoid antigen (BPAG2), a hemidesmosomal transmembrane collagen (COL17A1), in generalized atrophic benign epidermolysis bullosa

Junctional epidermolysis bullosa (JEB) is a heterogeneous autosomal recessively inherited blistering skin disorder associated with fragility at the dermal-epidermal junction. Characteristic ultrastructural findings in JEB are abnormalities in the hemidesmosome-anchoring filament complexes. These focal attachment structures, which extend from the intracellular compartment of the basal keratinocytes to the underlying basement membrane, have been shown to be hypoplastic or rudimentary in different forms of JEB. Previously, in different JEB phenotypes, mutations have been found in the three genes for the anchoring filament component laminin 5 (LAMA3, LAMB3, and LAMC2) and in the gene for the hemidesmosome-associated integrin beta 4 subunit. Here, we describe the first mutations in the gene encoding the 180-kD bullous pemphigoid antigen (BPAG2), a transmembranous hemidesmosomal collagen, also known as type XVII collagen (COL17A1). The patient is affected with generalized atrophic benign epidermolysis bullosa (GABEB), a rare variant of JEB, and is a compound heterozygote for premature termination codons on both alleles. These novel findings emphasize the molecular heterogeneity of this group of genodermatoses, and attest to the importance of BPAG2 in maintaining adhesion between the epidermis and the dermis.

Diminished expression of the extracellular domain of bullous pemphigoid antigen 2 (BPAG2) in the epidermal basement membrane of patients with generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa (GABEB) is a nonlethal form of junctional epidermolysis bullosa characterized by generalized skin and mucosal blisters that heal with atrophy; other features include alopecia, nail dystrophy, large melanocytic nevi, and autosomal recessive inheritance. The specific aim of this study was to identify an abnormality in epidermal basement membrane adhesion molecules in well characterized GABEB patients that would explain why these subjects' epidermis separates from their epidermal basement membrane. Cryostat sections of nonlesional skin from 8 GABEB patients in 5 different families as well as skin from normal volunteers (controls) were studied by indirect immunofluorescence microscopy using rabbit antiserum directed against a BPAG1 fusion protein or monoclonal antibodies directed against the extracellular domain of BPAG2 (HD18 and 233), epiligrin (P1E1), laminin 5 (GB3), types IV and VII collagen, or integrin subunits alpha 2, alpha 3, beta 1, alpha 6, or beta 4. In these studies, monoclonal antibodies HD18 and 233 showed no reactivity and diminished reactivity, respectively, to the epidermal BM of all GABEB patients. Interestingly, in one patient, the absent or diminished reactivities of monoclonal anti-BPAG2 antibodies were limited to well demarcated portions of an otherwise intact epidermal basement membrane. Moreover, BPAG1, epiligrin, laminin 5, types IV and VII collagen, and all integrin subunits under study were expressed in the same manner in both GABEB and normal human skin. These findings identify an abnormality in the extracellular domain of BPAG2 in the skin of GABEB patients. BPAG2 (type XVII collagen) is a transmembrane, hemidesmosome-associated molecule whose extracellular domain resides at the exact level where blisters develop in the skin of patients with GABEB.(ABSTRACT TRUNCATED AT 250 WORDS)

180-kD bullous pemphigoid antigen (BP180) is deficient in generalized atrophic benign epidermolysis bullosa.

Generalized atrophic benign epidermolysis bullosa (GABEB) is a form of nonlethal junctional epidermolysis bullosa characterized by universal alopecia and atrophy of the skin. We report a deficiency of the 180-kD bullous pemphigoid antigen in three patients with GABEB from unrelated families. We screened specimens of clinically normal skin from nine junctional epidermolysis bullosa patients (3 GABEB, 4 lethal, 1 cicatricial, 1 pretibial) by immunofluorescence using monoclonal antibodies to the 180-kD and 230-kD bullous pemphigoid antigens (BP180 and BP230). In the skin of the three GABEB patients there was no reactivity with antibodies to BP180, whereas staining for BP230 was normal. In the skin of the other six, non-GABEB patients, included in this study the expression of BP180 and BP230 was normal. Immunoblot analysis of cultured keratinocytes from one of the GABEB patients also failed to detect BP180 antigen, whereas BP230 was present in normal amounts. The deficient expression of BP180 is reflected in the RNA message, as in Northern blot analysis a reduced amount of BP180 transcripts, although of normal length, were detected. Interestingly, in another GABEB patient there were not-involved areas of skin, in which blistering could not be induced by rubbing. Biopsy material from these areas showed interrupted staining for BP180. There was no staining for BP180 in areas of clinically normal but involved skin of this patient. In conclusion, this study reveals that the BP180 antigen is deficient and the BP180 mRNA is reduced in generalized atrophic benign epidermolysis bullosa.