Genetic studies of 20 Japanese families of dystrophic epidermolysis bullosa

Molecular genetic basis of epidermolysis bullosa

Epidermolysis bullosa (EB) is an inherited disorder of skin fragility, caused by mutations in a large number of genes associated with skin integrity and dermal-epidermal adhesion. Skin fragility is manifested by a decrease in resistance to external mechanical influences, the clinical signs of which are the formation of blisters, erosions and wounds on the skin and mucous membranes. EB is a multisystemic disease and characterized by a wide phenotypic spectrum with extracutaneous complications in severe types, besides the skin and mucous membranes, with high mortality. More than 30 clinical subtypes have been identified, which are grouped into four main types: simplex EB, junctional EB, dystrophic EB and Kindler syndrome. To date, pathogenic variants in 16 different genes are associated with EB and encode proteins that are part of the skin anchoring structures or are signaling proteins. Genetic mutations cause dysfunction of cellular structures, differentiation, proliferation and apoptosis of cells, leading to mechanical instability of the skin. The formation of reduced proteins or decrease in their level leads mainly to functional disorders, forming mild or intermediate severe phenotypes. Absent protein expression is a result of null genetic variants and leads to structural abnormalities, causing a severe clinical phenotype. For most of the genes involved in the pathogenesis of EB, certain relationships have been established between the type and position of genetic variant and the severity of the clinical manifestations of the disease. Establishing an accurate diagnosis depends on the correlation of clinical, genealogical and immunohistological data in combination with molecular genetic testing. In general, the study of clinical, genetic and ultrastructural changes in EB has significantly expanded the understanding of the natural history of the disease and supplemented the data on genotype-phenotype correlations, promotes the search and study of epigenetic and non-genetic disease modifier factors, and also allows developing approaches to radical treatment of the disease. New advances of sequencing technologies have made it possible to describe new phenotypes and study their genetic and molecular mechanisms. This article describes the pathogenetic aspects and genes that cause main and rare syndromic subtypes of EB.

Generation of a recessive dystrophic epidermolysis bullosa mouse model with patient-derived compound heterozygous mutations

Recessive dystrophic epidermolysis bullosa (RDEB) is an intractable genetic disease of the skin caused by mutations in the COL7A1 gene. The majority of patients with RDEB harbor compound heterozygous mutations-two distinct mutations on each chromosome-without any apparent hotspots in the COL7A1 mutation pattern. This situation has made it challenging to establish a reliable RDEB mouse model with mutations that accurately mimic the genomic background of patients. Here, we established an RDEB mouse model harboring patient-type mutations in a compound heterozygous manner, using the CRISPR-based genome-editing technology i-GONAD. We selected two mutations, c.5818delC and E2857X, that have frequently been identified in cohorts of Japanese patients with RDEB. These mutations were introduced into the mouse genome at locations corresponding to those identified in patients. Mice homozygous for the 5818delC mutation developed severe RDEB-like phenotypes and died immediately after birth, whereas E2857X homozygous mice did not have a shortened lifespan compared to wild-type mice. Adult E2857X homozygous mice showed hair abnormalities, syndactyly, and nail dystrophy; these findings indicate that E2857X is indeed pathogenic in mice. Mice with the c.5818delC/E2857X compound heterozygous mutation presented an intermediate phenotype between the c.5818delC and E2857X homozygous mice. Single-cell RNA sequencing further clarified that the intrafollicular keratinocytes in c.5818delC/E2857X compound heterozygous mice exhibited abnormalities in cell cycle regulation. The proposed strategy to produce compound heterozygous mice, in addition to the established mouse line, will facilitate research on RDEB pathogenesis to develop a cure for this devastating disease.

Novel pathogenic variants in an Indian cohort with epidermolysis bullosa: Expanding the genotypic spectrum

BACKGROUND

Epidermolysis bullosa (EB) is a genodermatosis characterized by skin fragility and blisters with variable severity. Patients with Dystrophic EB (DEB) or Junctional EB (JEB) mainly present to clinic due to greater functional impairment. Pathogenic sequence variations in COL7A1 are implicated in DEB.

OBJECTIVE

We have tried to decipher the molecular spectrum and genotype phenotype correlation of 21 Indian patients with EB.

METHODS

Next generation sequencing (NGS) was performed to determine the pathogenic variants. Sanger sequencing was also done for validation of the variants in eleven individuals.

RESULTS

Pathogenic variants were detected in 20 individuals (diagnostic yield of 95%). Majority of them (90%) had sequence variation in COL7A1 while two had pathogenic variants in ITGB4 and KRT14 respectively. Out of the 18 patients confirmed to have DEB, 3 had Dominant DEB (DDEB) whereas 15 patients had Recessive DEB (RDEB). Amongst 23 sequence variations identified, 12 were found to be novel (3 were missense, 5 were premature termination codon variants while 4 were splice-site changes).

CONCLUSION

Genotype phenotype correlation was noted with milder manifestations in those with dominant inheritance types. Exact molecular diagnosis can be ascertained by NGS in majority of cases.

An overview of the genetic basis of epidermolysis bullosa in Brazil: discovery of novel and recurrent disease-causing variants

Epidermolysis bullosa (EB) is a genodermatosis that encompasses a group of clinically and genetically heterogeneous disorders classified in four major types: EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB) and Kindler syndrome. Our aim was to characterize recurrent and novel mutations associated to EB in a sample of Brazilian patients. Eighty-seven patients (25 EBS, 4 JEB and 58 DEB) were studied. We performed a next-generation sequencing-based multigene panel through ion torrent technology including 11 genes: KRT5, KRT14, PLEC, TGM5, LAMA3, LAMB3, LAMC2, COL17A1, ITGB4, COL7A1, and FERMT1. A total of 72 different pathogenic or likely pathogenic variants were identified, 32 of them are novel. The causal variant was detected in 82 patients (efficiency of 94.3%). Pathogenic variants in the residue 125 of KRT14 were identified in 32% of all EBS patients. In DEB patients, four COL7A1 variants were quite frequent, some of them clustered in specific Brazilian regions. Our study extends the spectrum of known mutations in EB and describes, for the first time, the genetic profile of EB patients from Brazil.

Cultured Epidermal Autografts from Clinically Revertant Skin as a Potential Wound Treatment for Recessive Dystrophic Epidermolysis Bullosa

Inherited skin disorders have been reported recently to have sporadic normal-looking areas, where a portion of the keratinocytes have recovered from causative gene mutations (revertant mosaicism). We observed a case of recessive dystrophic epidermolysis bullosa treated with cultured epidermal autografts (CEAs), whose CEA-grafted site remained epithelized for 16 years. We proved that the CEA product and the grafted area included cells with revertant mosaicism. Based on these findings, we conducted an investigator-initiated clinical trial of CEAs from clinically revertant skin for recessive dystrophic epidermolysis bullosa. The donor sites were analyzed by genetic analysis, immunofluorescence, electron microscopy, and quantification of the reverted mRNA with deep sequencing. The primary endpoint was the ulcer epithelization rate per patient at 4 weeks after the last CEA application. Three patients with recessive dystrophic epidermolysis bullosa with 8 ulcers were enrolled, and the epithelization rate for each patient at the primary endpoint was 87.7%, 100%, and 57.0%, respectively. The clinical effects were found to persist for at least 76 weeks after CEA transplantation. One of the three patients had apparent revertant mosaicism in the donor skin and in the post-transplanted area. CEAs from clinically normal skin are a potentially well-tolerated treatment for recessive dystrophic epidermolysis bullosa.

The development of induced pluripotent stem cell-derived mesenchymal stem/stromal cells from normal human and RDEB epidermal keratinocytes

BACKGROUND

Epidermolysis bullosa (EB) is a group of hereditary disorders caused by mutations in the genes encoding structural molecules of the dermal-epidermal junction (DEJ). Cell-based therapies such as allogeneic mesenchymal stem/stromal cell (MSC) transplantation have recently been explored for severe EB types, such as recessive dystrophic EB (RDEB). However, hurdles exist in current MSC-based therapies, such as limited proliferation from a single cell source and limited cell survival due to potential allogenic rejection.

OBJECTIVES

We aimed to develop MSCs from keratinocyte-derived induced pluripotent stem cells (iPSCs).

METHODS

Keratinocyte-derived iPSCs (KC-iPSCs) of a healthy human and an RDEB patient were cultured with activin A, 6-bromoindirubin-3'-oxime and bone morphogenetic protein 4 to induce mesodermal lineage formation. These induced cells were subjected to immunohistochemical analysis, flow cytometric analysis and RNA microarray analysis in vitro, and were injected subcutaneously and intravenously to wounded immunodeficient mice to assess their wound-healing efficacy.

RESULTS

After their induction, KC-iPSC-induced cells were found to be compatible with MSCs. Furthermore, with the subcutaneous and intravenous injection of the KC-iPSC-induced cells into wounded immunodeficient mice, human type VII collagen was detected at the DEJ of epithelized areas.

CONCLUSIONS

We successfully established iPSC-derived MSCs from keratinocytes (KC-iPSC-MSCs) of a normal human and an RDEB patient. KC-iPSC-MSCs may have potential in therapies for RDEB.

A comprehensive next-generation sequencing assay for the diagnosis of epidermolysis bullosa

BACKGROUND

Historically, diagnosis of epidermolysis bullosa has required skin biopsies for electron microscopy, direct immunofluorescence to determine which gene(s) to choose for genetic testing, or both.

METHODS

To avoid these invasive tests, we developed a high-throughput next-generation sequencing (NGS)-based diagnostic assay called EBSEQ that allows simultaneous detection of mutations in 21 genes with known roles in epidermolysis bullosa pathogenicity. Mutations are confirmed with traditional Sanger sequencing.

RESULTS

We present our EBSEQ assay and preliminary studies on the first 43 subjects tested. We identified 11 cases of epidermolysis bullosa simplex, five cases of junctional epidermolysis bullosa, 11 cases of dominant dystrophic epidermolysis bullosa, 15 cases of recessive dystrophic epidermolysis bullosa, and one case that remains without diagnosis. We also found an additional 52 variants of uncertain clinical significance in 17 of the 21 epidermolysis bullosa-associated genes tested. Three of the variants of uncertain clinical significance were also found in three other patients, for a total of 49 unique variants of uncertain clinical significance. We found the clinical sensitivity of the assay to be 75% to 98% and the analytical sensitivity to be 99% in identifying base substitutions and small deletions and duplications. Turnaround time was 3 to 6 weeks.

CONCLUSIONS

EBSEQ is a sensitive, relatively rapid, minimally invasive, comprehensive genetic assay for the diagnosis of epidermolysis bullosa.

Establishment of integration-free induced pluripotent stem cells from human recessive dystrophic epidermolysis bullosa keratinocytes

BACKGROUND

Induced pluripotent stem cell (iPSC) technology enables patient-specific pluripotent stem cells to be derived from adult somatic cells without the use of an embryonic cell source. To date, recessive dystrophic epidermolysis bullosa (RDEB)-specific iPSCs have been generated from patients using integrating retroviral vectors. However, vector integration into the host genome can endanger the biosafety and differentiation propensities of iPSCs. Although various integration-free reprogramming systems have been reported, their utility in reprogramming somatic cells from patients remains largely undetermined.

OBJECTIVE

Our study aims to establish safe iPSCs from keratinocytes of RDEB patients using non-integration vector.

METHOD

We optimized and infected non-integrating Sendai viral vectors to reprogram keratinocytes from healthy volunteers and RDEB patients.

RESULTS

Sendai vector infection led to the reproducible generation of genomic modification-free iPSCs from these keratinocytes, which was proved by immunohistochemistry, reverse transcription polymerase chain reaction, methylation assay, teratoma assay and embryoid body formation assay. Furthermore, we confirmed that these iPSCs have the potential to differentiate into dermal fibroblasts and epidermal keratinocytes.

CONCLUSION

This is the first report to prove that the Sendai vector system facilitates the reliable reprogramming of patient keratinocytes into transgene-free iPSCs, providing another pluripotent platform for personalized diagnostic and therapeutic approaches to RDEB.

Type VII collagen deficiency causes defective tooth enamel formation due to poor differentiation of ameloblasts

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by mutations in the gene encoding type VII collagen (COL7), a major component of anchoring fibrils in the epidermal basement membrane zone. Patients with RDEB present a low oral hygiene index and prevalent tooth abnormalities with caries. We examined the tooth enamel structure of an RDEB patient by scanning electron microscopy. It showed irregular enamel prisms, indicating structural enamel defects. To elucidate the pathomechanisms of enamel defects due to COL7 deficiency, we investigated tooth formation in Col7a1(-/-) and COL7-rescued humanized mice that we have established. The enamel from Col7a1(-/-) mice had normal surface structure. The enamel calcification and chemical composition of Col7a1(-/-) mice were similar to those of the wild type. However, transverse sections of teeth from the Col7a1(-/-) mice showed irregular enamel prisms, which were also observed in the RDEB patient. Furthermore, the Col7a1(-/-) mice teeth had poorly differentiated ameloblasts, lacking normal enamel protein-secreting Tomes' processes, and showed reduced mRNA expression of amelogenin and other enamel-related molecules. These enamel abnormalities were corrected in the COL7-rescued humanized mice expressing a human COL7A1 transgene. These findings suggest that COL7 regulates ameloblast differentiation and is essential for the formation of Tomes' processes. Collectively, COL7 deficiency is thought to disrupt epithelial-mesenchymal interactions, leading to defective ameloblast differentiation and enamel malformation in RDEB patients.

The international dystrophic epidermolysis bullosa patient registry: an online database of dystrophic epidermolysis bullosa patients and their COL7A1 mutations

Dystrophic epidermolysis bullosa (DEB) is a heritable blistering disorder that can be inherited autosomal dominantly (DDEB) or recessively (RDEB) and covers a group of several distinctive phenotypes. A large number of unique COL7A1 mutations have been shown to underlie DEB. Although general genotype-phenotype correlation rules have emerged, many exceptions to these rules exist, compromising disease diagnosing and genetic counseling. We therefore constructed the International DEB Patient Registry (http://www.deb-central.org), aimed at worldwide collection and sharing of phenotypic and genotypic information on DEB. As of May 2011, this MOLGENIS-based registry contains detailed information on 508 published and 71 unpublished patients and their 388 unique COL7A1 mutations, and includes all combinations of mutations. The current registry RDEB versus DDEB ratio of 4:1, if compared to prevalence figures, suggests underreporting of DDEB in the literature. Thirty-eight percent of mutations stored introduce a premature termination codon (PTC) and 43% an amino acid change. Submission wizards allow users to quickly and easily share novel information. This registry will be of great help in disease diagnosing and genetic counseling and will lead to novel insights, especially in the rare phenotypes of which there is often lack of understanding. Altogether, this registry will greatly benefit the DEB patients.

Two cases of recessive dystrophic epidermolysis bullosa diagnosed as severe generalized

Recessive dystrophic epidermolysis bullosa (RDEB) is a congenital bullous disease resulting from defective anchoring fibrils at the dermal-epidermal junction and mutations in the type VII collagen gene. In this report, we describe two patients with severe generalized RDEB. Patient 1 was a 24-day-old male infant, and patient 2 was a 1-day-old female infant. Immunofluorescence microscopy demonstrated absence of type VII collagen labeling in a skin sample of patient 1, and reduced staining in patient 2. Electron microscopy revealed absence of anchoring fibrils below the lamina densa in patient 1, and reduced or rudimentary anchoring fibrils in patient 2. Mutation analyses of COL7A1 in these patients revealed heteroallelic recessive mutations which resulted in premature termination codons (PTC): 6573+1G>C in intron81 and 886del6ins14 in exon 7 in patient 1, and 6573+1G>C in intron81 and 4535insC in exon 44 in patient 2. Heteroallelic combinations of PTC mutation generally result in the severe generalized type. Patient 2 has developed a digital fusion at age 2, which is a typical manifestation of severe generalized RDEB. The RDEB subtype is considered to be determined based on comprehensive information, including analysis of alleles, protein expression, ultrastructure and clinical symptoms after growth. However, mutation analyses of COL7A1 can provide valuable information estimating a diagnosis in early infancy.

Epidermolysis bullosa in Japan

Epidermolysis bullosa (EB) is a group of hereditary disorders characterized by mechanical stress-induced blistering of the skin and mucous membranes. This article discusses the prevalence among and genetic studies of Japanese patients with EB.

A novel COL7A1 gene mutation in an Iranian individual suffering dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa is a heritable skin disorder with dominant and recessive genetic patterns. Numerous studies underline that both forms are caused by mutations of the COL7A1 gene, which encodes collagen type VII. It has been reported that most mutations detected in the recessive disease form are nonsense mutations or small insertions or deletions leading to frameshift and premature translational termination, which tend to produce severe phenotypes. In contrast, missense mutations causing amino acid substitutions, which result in variable phenotypes, predominate in the dominant form of dystrophic epidermolysis bullosa. Genomic DNA from the patient and parents was subjected to PCR amplification of the coding region of the COL7A1 gene. Direct sequencing of the PCR products revealed a homozygous single-base deletion in the patient (c.6269-6270delC). The parents were heterozygous for the same mutation. This deletion is a novel mutation in the human COL7A1 gene based on comparisons with the Human Genome Mutation Database. To our knowledge, this is the first report of dystrophic epidermolysis bullosa in an Iranian patient confirmed by molecular diagnosis.

Keratinocyte-/fibroblast-targeted rescue of Col7a1-disrupted mice and generation of an exact dystrophic epidermolysis bullosa model using a human COL7A1 mutation

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe hereditary bullous disease caused by mutations in COL7A1, which encodes type VII collagen (COL7). Col7a1 knockout mice (COL7(m-/-)) exhibit a severe RDEB phenotype and die within a few days after birth. Toward developing novel approaches for treating patients with RDEB, we attempted to rescue COL7(m-/-) mice by introducing human COL7A1 cDNA. We first generated transgenic mice that express human COL7A1 cDNA specifically in either epidermal keratinocytes or dermal fibroblasts. We then performed transgenic rescue experiments by crossing these transgenic mice with COL7(m+/-) heterozygous mice. Surprisingly, human COL7 expressed by keratinocytes or by fibroblasts was able to rescue all of the abnormal phenotypic manifestations of the COL7(m-/-) mice, indicating that fibroblasts as well as keratinocytes are potential targets for RDEB gene therapy. Furthermore, we generated transgenic mice with a premature termination codon expressing truncated COL7 protein and performed the same rescue experiments. Notably, the COL7(m-/-) mice rescued with the human COL7A1 allele were able to survive despite demonstrating clinical manifestations very similar to those of human RDEB, indicating that we were able to generate surviving animal models of RDEB with a mutated human COL7A1 gene. This model has great potential for future research into the pathomechanisms of dystrophic epidermolysis bullosa and the development of gene therapies for patients with dystrophic epidermolysis bullosa.

Mutation analysis and characterization of COL7A1 mutations in dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is inherited in both an autosomal dominant DEB and autosomal recessive manner RDEB, both of which result from mutations in the type VII collagen gene (COL7A1). To date, 324 pathogenic mutations have been detected within COL7A1 in different variants of DEB; many mutations are clustered in exon 73 (10.74%) which is close to the 39 amino acid interruption region. Dominant dystrophic epidermolysis bullosa usually involves glycine substitutions within the triple helix of COL7A1 although other missense mutations, deletions or splice-site mutations may underlie some cases. In recessive dystrophic epidermolysis bullosa, the mutations include nonsense, splice site, deletions or insertions, 'silent' glycine substitutions within the triple helix and non-glycine missense mutations within the triple helix or non-collagenous NC-2 domain. The nature of mutations in COL7A1 and their positions correlate reasonably logically with the severity of the resulting phenotypes.

Genotype-phenotype correlations in six Japanese patients with recessive dystrophic epidermolysis bullosa with the recurrent p.Glu2857X mutation

BACKGROUND

General genotype-phenotype correlations have been delineated in recessive dystrophic epidermolysis bullosa (RDEB), but these remain complicated and it is still difficult to assess the clinical consequences of individual COL7A1 mutations.

OBJECTIVE

To characterize recurrent p.Glu2857X mutations and show how other COL7A1 mutations influence the phenotype in RDEB patients harboring p.Glu2857X.

METHODS

Genotype-phenotype correlations were studied in six Japanese RDEB patients with the p.Glu2857X mutation.

RESULTS

Besides the common p.Glu2857X mutation, premature termination codon (PTC) mutations were found in three patients, glycine substitution missense mutations in two patients, and a non-glycine substitution missense mutation in one patient. PTC mutations in both alleles generally cause the most severe, mutilating Hallopeau-Siemens (HS) variant of RDEB, whereas none of the PTC mutations resulted in severe phenotypes consistent with the HS subtype when coupled with p.Glu2857X. Missense glycine and non-glycine mutations caused phenotypes of differing severity, suggesting that the extent of destabilization of anchoring fibrils depends on the type of mutation.

CONCLUSION

A p.Glu2857X mutation exhibits mild pathogenic effects compared to other PTC mutations in COL7A1, and its uniqueness enables detailed analysis and comparison of the destabilizing effects of missense mutations in RDEB patients.

Clinical and molecular dilemmas in the diagnosis of familial epidermolysis bullosa pruriginosa

Dystrophic epidermolysis bullosa is a rare and clinically heterogeneous mechanobullous disorder. One unusual clinical variant is epidermolysis bullosa pruriginosa (EBP), in which the combination of pruritus and skin fragility can lead to hypertrophic, lichenified nodules and plaques. This form of inherited epidermolysis bullosa may not develop clinically until adult life, leading to diagnostic confusion with acquired disorders, such as nodular prurigo, lichen simplex, lichen planus, hypertrophic scarring, or dermatitis artefacta. As in all other forms of dystrophic epidermolysis bullosa, the molecular pathology involves mutations in the gene encoding the anchoring fibril protein, type VII collagen (COL7A1), but there is no clear genotype-phenotype correlation in EBP. In this report, we describe a Chinese-Singaporean family with EBP in whom an autosomal dominant glycine substitution mutation, p.G2251E, was identified in exon 86 of the COL7A1 gene. This heterozygous mutation was identified in the genomic DNA of all 4 affected adults tested, as well as 2 clinically unaffected offspring (aged 9-29 years). Based on DNA sequencing, we predict that these individuals may develop EBP later in life, although additional factors leading to disease expression may determine phenotypic expression. Nevertheless, we plan to closely monitor these potentially presymptomatic individuals for symptoms of pruritus and early signs of the genetic disorder.

Targeted skipping of a single exon harboring a premature termination codon mutation: implications and potential for gene correction therapy for selective dystrophic epidermolysis bullosa patients

This study examined the feasibility of antisense oligoribonucleotide (AON) therapy for dystrophic epidermolysis bullosa (DEB). AON was designed to induce skipping of a targeted exon containing a premature termination codon mutation, resulting in restoration of the open reading frame. We targeted exon 70 of COL7A1, as a recurrent mutation 5818delC in Japanese DEB patients was localized to exon 70. We found that one AON induced effective skipping of normal exon 70 containing 16 amino acids. Attachment and migration analyses showed that recombinant collagen without contribution of exon 70 was similar in effect to normal type VII collagen. Next, we synthesized mutation-specific AON by deleting cytosine at 5818. Introduction of this AON into DEB keratinocytes harboring 5818delC showed that the AON induced skipping of exon 70 in the abnormal 5818delC allele. Furthermore, 6.2% of DEB keratinocytes started to express type VII collagen in vitro after application of the mutation-specific AON. Injection of the AON into rat model grafted with DEB keratinocytes and fibroblasts induced a low amount of type VII collagen expression. We conclude that skipping of targeted exons using mutation-specific AON may show potential for future gene therapy for DEB patients.

COL7A1 mutation G2037E causes epidermal retention of type VII collagen

COL7A1 glycine substitution (GS) mutations result in dominant and recessive dystrophic epidermolysis bullosa (DDEB and RDEB). Here, we report a DDEB family in which retention of type VII collagen by epidermal keratinocytes was observed for a female proband. Mutational analysis detected a GS mutation, G2037E, in the proband and her affected father. To demonstrate direct association of G2037E and type VII collagen retention we introduced this mutated COL7A1 gene into cultured keratinocytes using retroviral methods. This mutation was dominant, so we transferred a 1:1 mixture of wild-type (unaffected) and G2037E-mutated COL7A1, together, in addition to the unaffected gene or the mutated gene alone. The increase in type VII collagen cytoplasmic staining in the G2037E/wild transfectant cell samples was compared with that for control/wild-type cells. Intracellular collagen VII staining in the G2037E (alone)-transfected cells was even stronger than for the G2037E/wild transfection sample. These results indicate that the G2037E COL7A1 mutation leads to increased epidermal retention of type VII collagen in vivo, and also suggests that homozygotes carrying this dominant GS mutation may have more severe phenotypes than heterozygotes. This study furthers our understanding of GS COL7A1 mutations in DEB.