Humans with inherited T cell CD28 deficiency are susceptible to skin papillomaviruses but are otherwise healthy.

We study a patient with the human papilloma virus (HPV)-2-driven "tree-man" phenotype and two relatives with unusually severe HPV4-driven warts. The giant horns form an HPV-2-driven multifocal benign epithelial tumor overexpressing viral oncogenes in the epidermis basal layer. The patients are unexpectedly homozygous for a private CD28 variant. They have no detectable CD28 on their T cells, with the exception of a small contingent of revertant memory CD4+ T cells. T cell development is barely affected, and T cells respond to CD3 and CD2, but not CD28, costimulation. Although the patients do not display HPV-2- and HPV-4-reactive CD4+ T cells in vitro, they make antibodies specific for both viruses in vivo. CD28-deficient mice are susceptible to cutaneous infections with the mouse papillomavirus MmuPV1. The control of HPV-2 and HPV-4 in keratinocytes is dependent on the T cell CD28 co-activation pathway. Surprisingly, human CD28-dependent T cell responses are largely redundant for protective immunity.

Splice modulation strategy applied to deep intronic variants in COL7A1 causing recessive dystrophic epidermolysis bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare and most often severe genetic disease characterized by recurrent blistering and erosions of the skin and mucous membranes after minor trauma, leading to major local and systemic complications. The disease is caused by loss-of-function variants in COL7A1 encoding type VII collagen (C7), the main component of anchoring fibrils, which form attachment structures stabilizing the cutaneous basement membrane zone. Alterations in C7 protein structure and/or expression lead to abnormal, rare or absent anchoring fibrils resulting in loss of dermal-epidermal adherence and skin blistering. To date, more than 1,200 distinct COL7A1 deleterious variants have been reported and 19% are splice variants. Here, we describe two RDEB patients for whom we identified two pathogenic deep intronic pathogenic variants in COL7A1. One of these variants (c.7795-97C > G) promotes the inclusion of a pseudoexon between exons 104 and 105 in the COL7A1 transcript, while the other causes partial or complete retention of intron 51. We used antisense oligonucleotide (ASO) mediated exon skipping to correct these aberrant splicing events in vitro. This led to increased normal mRNA splicing above 94% and restoration of C7 protein expression at a level (up to 56%) that should be sufficient to reverse the phenotype. This first report of exon skipping applied to counteract deep intronic variants in COL7A1 represents a promising therapeutic strategy for personalized medicine directed at patients with intronic variants at a distance of consensus splice sites.

Diagnosis of Epidermolysis Bullosa Acquisita: Multicentre Comparison of Different Assays for Serum Anti-type VII Collagen Reactivity.

Epidermolysis bullosa acquisita is a pemphigoid disease characterized by autoantibodies against type VII collagen. This study compared the sensitivity and specificity of 6 diagnostic assays: type VII collagen non-collagenous domains enzyme-linked immunoassay (NC1/2 ELISA) (MBL, Nagoya, Japan); type VII collagen NC1 ELISA (Euroimmun, Lübeck, Germany); indirect immunofluorescence (IF) microscopy test based on the expression of recombinant NC1 in a human cell line (NC1 BIOCHIP®; Euroimmun); full-length recombinant type VII collagen ELISA; immunoblotting with full-length type VII collagen in the extract of human dermis; and immunoblotting with recombinant NC1. Immunoblotting with recombinant NC1 showed a sensitivity of 93.1% and specificity of 100%, follow-ed by NC1 BIOCHIP® (sensitivity, 89.1%; specificity, 100%), immunoblotting with human dermis (sensitivity, 87.1%; specificity 100%), NC1-ELISA (sensitivity 82.2%; specificity 98.6%), NC1/NC2 ELISA (sensitivity 88.1%; specificity 93.3%), and full-length type VII collagen ELISA (sensitivity 80.2%; specificity 93.8%).

Emerging drugs for the treatment of epidermolysis bullosa.

INTRODUCTION: Epidermolysis Bullosa (EB) form a heterogeneous group of rare, sometimes life-threatening inherited skin diseases characterized by skin and mucosal blistering after mild trauma from birth. They display a wide range of disease severity, with multiple local and systemic complications with no satisfactory treatment. AREAS COVERED: Approaches aiming to restore the functional expression of the defective protein such as ex vivo and in vivo gene therapy, cell therapies, protein replacement and pharmacological approaches have shown promising results. In addition, improved knowledge of EB pathogenesis has open the way to symptom-relief therapies using repurposed drugs in some forms of EB. EXPERT OPINION: A cure for all forms of EB will remain challenging, but it is anticipated that treatments for EB will rely on precision medicine, involving a combination of complementary approaches. Treatments aiming to restore the function of the defective genes will be combined with symptom-relief therapies to address the specific features of the different forms of EB and each patient complications. A growing number of biotech and pharmaceutical companies have shown an increasing interest in the treatment of EB and as a result, have implemented numerous clinical trials. Therefore, we anticipate the emergence of effective treatments in the near future.

Epidermolysis bullosa simplex-generalized severe type due to keratin 5 p.Glu477Lys mutation: Genotype-phenotype correlation and in silico modeling analysis.

BACKGROUND/OBJECTIVES: Epidermolysis bullosa is a group of diseases caused by mutations in skin structural proteins. Availability of genetic sequencing makes identification of causative mutations easier, and genotype-phenotype description and correlation are important. We describe six patients with a keratin 5 mutation resulting in a glutamic acid to lysine substitution at position 477 (p.Glu477Lys) who have a distinctive, severe and sometimes fatal phenotype. We also perform in silico modeling to show protein structural changes resulting in instability. METHODS: In this case series, we collected clinical data from six patients with this mutation identified from their national or local epidermolysis bullosa databases. We performed in silico modeling of the keratin 5-keratin 14 coil 2B complex using CCBuilder and rendered with Pymol (Schrodinger, LLC, New York, NY). RESULTS: Features include aplasia cutis congenita, generalized blistering, palmoplantar keratoderma, onychodystrophy, airway and developmental abnormalities, and a distinctive reticulated skin pattern. Our in silico model of the keratin 5 p.Glu477Lys mutation predicts conformational change and modification of the surface charge of the keratin heterodimer, severely impairing filament stability. CONCLUSIONS: Early recognition of the features of this genotype will improve care. In silico analysis of mutated keratin structures provides useful insights into structural instability.

Comparison of 3 type VII collagen (C7) assays for serologic diagnosis of epidermolysis bullosa acquisita (EBA).

BACKGROUND: Serologic diagnosis of epidermolysis bullosa acquisita (EBA) relies on the detection of circulating autoantibodies to type VII collagen (C7). OBJECTIVE: We sought to compare the diagnostic performances of a commercialized enzyme-linked immunosorbent assay (ELISA) using C7 noncollagenous (NC) domains (C7-NC1/NC2 ELISA) and indirect immunofluorescence (IIF) biochip test on NC1-C7-expressing transfected cells (IIFT), with a full-length-C7 ELISA developed in our laboratory. METHODS: C7-NC1/NC2 ELISA, IIFT, and full-length-C7 ELISA were run on 77 nonselected consecutive EBA sera. RESULTS: C7-NC1/NC2 ELISA, IIFT, and full-length-C7 ELISA were positive, respectively, for: 30%, 27%, and 65% of the 77 sera; 43%, 32%, and 80% of 44 sera labeling the salt-split-skin (SSS) floor (F) by IIF (SSS/F(+)); 9%, 22%, and 47% of 32 SSS/F(-) sera; 28%, 28%, and 58% of classic EBA; 41%, 41%, and 82% of inflammatory EBA; and 18%, 0%, and 55% of mucous-membrane-predominant EBA. Significant differences for all sera were found between: the 2 ELISAs for the 77 sera, SSS/F(+) and SSS/F(-) sera, and IIFT versus full-length-C7 ELISA. LIMITATIONS: The retrospective design was a limitation. CONCLUSION: C7-NC1/NC2 ELISA and IIFT sensitivities for serologic diagnoses of EBA were low. Full-length-C7 ELISA was significantly more sensitive and could serve as a reference test.

Citrullinated Histone H3, a Marker for Neutrophil Extracellular Traps, Is Associated with Poor Prognosis in Cutaneous Squamous Cell Carcinoma Developing in Patients with Recessive Dystrophic Epidermolysis Bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare severe hereditary skin disease characterized by skin and mucosa fragility, resulting in blister formation. The most severe complication in RDEB patients is the development of cutaneous squamous cell carcinoma (SCC), leading to premature death. There is a great deal of evidence suggesting a permissive tumor microenvironment (TME) as a driver of SCC development in RDEB patients. In a cohort of RDEB patients, we characterized the immune profiles of RDEB-SCCs and compared them with clinical, histopathological, and prognostic features. RDEB-SCCs were subdivided into four groups based on their occurrence (first onset or recurrences) and grading according to clinical, histopathological parameters of aggressiveness. Thirty-eight SCCs from 20 RDEB patients were analyzed. Five RDEB patients experienced an unfavorable course after the diagnosis of the first SCC, with early recurrence or metastasis, whereas 15 patients developed multiple SCCs without metastasis. High-risk primary RDEB-SCCs showed a higher neutrophil-to-lymphocyte ratio in the tumor microenvironment and an increased proportion of neutrophil extracellular traps (NETs). Additionally, citrullinated histone H3, a marker of NETs, was increased in the serum of RDEB patients with high-risk primary SCC, suggesting that this modified form of histone H3 may serve as a potential blood marker of unfavorable prognosis in RDEB-SCCs.

Pachyonychia Congenita: A Research Agenda Leading to New Therapeutic Approaches.

Pachyonychia congenita (PC) is a dominantly inherited genetic disorder of cornification. PC stands out among other genodermatoses because despite its rarity, it has been the focus of a very large number of pioneering translational research efforts over the past 2 decades, mostly driven by a patient support organization, the Pachyonychia Congenita Project. These efforts have laid the ground for innovative strategies that may broadly impact approaches to the management of other inherited cutaneous and noncutaneous diseases. This article outlines current avenues of research in PC, expected outcomes, and potential hurdles.

Highly Efficient Ex Vivo Correction of COL7A1 through Ribonucleoprotein-Based CRISPR/Cas9 and Homology-Directed Repair to Treat Recessive Dystrophic Epidermolysis Bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare and severe genetic skin disease responsible for blistering of the skin and mucosa after minor trauma. RDEB is caused by a wide variety of variants in COL7A1 encoding type VII Collagen, the major component of anchoring fibrils that form key attachment structures for dermal-epidermal adherence. In this study, we achieved highly efficient COL7A1 editing in primary RDEB keratinocytes and fibroblasts from 2 patients homozygous for the c.6508C>T (p.Gln2170∗) variant through CRISPR/Cas9-mediated homology-directed repair. Three guide RNAs targeting the c.6508C>T variant or harboring sequences were delivered together with high-fidelity Cas9 as a ribonucleoprotein complex. Among them, one achieved 73% cleavage activity in primary RDEB keratinocytes and RDEB fibroblasts. Then, we treated RDEB keratinocytes and RDEB fibroblasts with this specific ribonucleoprotein complex and the corresponding donor template delivered as single-stranded oligodeoxynucleotide and achieved up to 58% of genetic correction as well as type VII Collagen rescue. Finally, grafting of corrected 3-dimensional skin onto nude mice induced re-expression and normal localization of type VII Collagen as well as anchoring fibril formation at the dermal-epidermal junction 5 and 10 weeks after grafting. With this promising nonviral approach, we achieved therapeutically relevant specific gene editing that could be applicable to all variants in exon 80 of COL7A1 in primary RDEB cells.

SIN retroviral vectors expressing COL7A1 under human promoters for ex vivo gene therapy of recessive dystrophic epidermolysis bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by loss-of-function mutations in COL7A1 encoding type VII collagen which forms key structures (anchoring fibrils) for dermal-epidermal adherence. Patients suffer since birth from skin blistering, and develop severe local and systemic complications resulting in poor prognosis. We lack a specific treatment for RDEB, but ex vivo gene transfer to epidermal stem cells shows a therapeutic potential. To minimize the risk of oncogenic events, we have developed new minimal self-inactivating (SIN) retroviral vectors in which the COL7A1 complementary DNA (cDNA) is under the control of the human elongation factor 1alpha (EF1alpha) or COL7A1 promoters. We show efficient ex vivo genetic correction of primary RDEB keratinocytes and fibroblasts without antibiotic selection, and use either of these genetically corrected cells to generate human skin equivalents (SEs) which were grafted onto immunodeficient mice. We achieved long-term expression of recombinant type VII collagen with restored dermal-epidermal adherence and anchoring fibril formation, demonstrating in vivo functional correction. In few cases, rearranged proviruses were detected, which were probably generated during the retrotranscription process. Despite this observation which should be taken under consideration for clinical application, this preclinical study paves the way for a therapy based on grafting the most severely affected skin areas of patients with fully autologous SEs genetically corrected using a SIN COL7A1 retroviral vector.

Transient mTOR inhibition rescues 4-1BB CAR-Tregs from tonic signal-induced dysfunction.

The use of chimeric antigen receptor (CAR)-engineered regulatory T cells (Tregs) has emerged as a promising strategy to promote immune tolerance. However, in conventional T cells (Tconvs), CAR expression is often associated with tonic signaling, which can induce CAR-T cell dysfunction. The extent and effects of CAR tonic signaling vary greatly according to the expression intensity and intrinsic properties of the CAR. Here, we show that the 4-1BB CSD-associated tonic signal yields a more dramatic effect in CAR-Tregs than in CAR-Tconvs with respect to activation and proliferation. Compared to CD28 CAR-Tregs, 4-1BB CAR-Tregs exhibit decreased lineage stability and reduced in vivo suppressive capacities. Transient exposure of 4-1BB CAR-Tregs to a Treg stabilizing cocktail, including an mTOR inhibitor and vitamin C, during ex vivo expansion sharply improves their in vivo function and expansion after adoptive transfer. This study demonstrates that the negative effects of 4-1BB tonic signaling in Tregs can be mitigated by transient mTOR inhibition.

Human fibroblasts share immunosuppressive properties with bone marrow mesenchymal stem cells.

INTRODUCTION: Bone marrow mesenchymal stem cells (BM-MSCs) and adipose tissue-derived stem cells share immunosuppressive capacities, suggesting that the latter could be a general property of stromal cells. METHODS: To check this hypothesis, we compared human BM-MSC and fibroblasts for their in vitro multi-potentiality, expandability and their immunomodulatory properties under normalized optimized culture conditions. RESULTS: We report that, unlike BM-MSCs, fibroblasts cannot differentiate in vitro into adipocytes and osteoblasts and differ from BM-MSCs by the expression of membrane CD106, CD10 and CD26 and by the expression of collagen VII mRNA. Like BM-MSCs, fibroblasts are unable to provoke in vitro allogeneic reactions, but strongly suppress lymphocyte proliferation induced by allogeneic mixed lymphocyte culture (MLC) or mitogens. We show that fibroblasts' immunosuppressive capacity is independent from prostaglandin E2, IL-10 and the tryptophan catabolising enzyme indoleamine 2,3-dioxygenase and is not abrogated after the depletion of CD8+ T lymphocytes, NK cells and monocytes. CONCLUSION: Finally, fibroblasts and BM-MSCs act at an early stage through blockage of lymphocyte activation, as demonstrated by down-regulation of GZMB (granzyme B) and IL2RA (CD25) expression.

Safety and early efficacy outcomes for lentiviral fibroblast gene therapy in recessive dystrophic epidermolysis bullosa.

BACKGROUNDRecessive dystrophic epidermolysis bullosa (RDEB) is a severe form of skin fragility disorder due to mutations in COL7A1 encoding basement membrane type VII collagen (C7), the main constituent of anchoring fibrils (AFs) in skin. We developed a self-inactivating lentiviral platform encoding a codon-optimized COL7A1 cDNA under the control of a human phosphoglycerate kinase promoter for phase I evaluation.METHODSIn this single-center, open-label phase I trial, 4 adults with RDEB each received 3 intradermal injections (~1 × 106 cells/cm2 of intact skin) of COL7A1-modified autologous fibroblasts and were followed up for 12 months. The primary outcome was safety, including autoimmune reactions against recombinant C7. Secondary outcomes included C7 expression, AF morphology, and presence of transgene in the injected skin.RESULTSGene-modified fibroblasts were well tolerated, without serious adverse reactions or autoimmune reactions against recombinant C7. Regarding efficacy, there was a significant (P < 0.05) 1.26-fold to 26.10-fold increase in C7 mean fluorescence intensity in the injected skin compared with noninjected skin in 3 of 4 subjects, with a sustained increase up to 12 months in 2 of 4 subjects. The presence of transgene (codon-optimized COL7A1 cDNA) was demonstrated in the injected skin at month 12 in 1 subject, but no new mature AFs were detected.CONCLUSIONTo our knowledge, this is the first human study demonstrating safety and potential efficacy of lentiviral fibroblast gene therapy with the presence of COL7A1 transgene and subsequent C7 restoration in vivo in treated skin at 1 year after gene therapy. These data provide a rationale for phase II studies for further clinical evaluation.TRIAL REGISTRATIONClincalTrials.gov NCT02493816.FUNDINGCure EB, Dystrophic Epidermolysis Bullosa Research Association (UK), UK NIHR Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London, and Fondation René Touraine Short-Exchange Award.

A frequent functional SNP in the MMP1 promoter is associated with higher disease severity in recessive dystrophic epidermolysis bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by mutations in the COL7A1 gene encoding type VII collagen. Variations in severity between the different clinical forms of RDEB likely depend on the nature and location of COL7A1 mutations, but observed intrafamilial phenotypic variations suggest additional genetic and/or environmental factors. Candidate modifier genes include MMP1, encoding matrix metalloproteinase 1, the first gene implicated in RDEB before its primary role in the disease was excluded. Type VII collagen is a substrate of MMP1 and an imbalance between its synthesis and degradation could conceivably worsen the RDEB phenotype. Here, we studied a previously described family with three affected siblings of identical COL7A1 genotype but displaying great sibling-to-sibling variations in disease severity. RDEB severity did not correlate with type VII collagen synthesis levels, but with protein levels at the dermal-epidermal junction, suggesting increased degradation by metalloproteinases. This was supported by the presence of increased transcript and active MMP1 levels in the most severely affected children, who carried a known SNP (1G/2G) in the MMP1 promoter. This SNP creates a functional Ets binding site resulting in transcriptional upregulation. We next studied a French cohort of 31 unrelated RDEB patients harboring at least one in-frame COL7A1 mutation, ranging from mild localized RDEB to the severe Hallopeau-Siemens form. We found a strong genetic association between the 2G variant and the Hallopeau-Siemens disease type (odds ratio: 73.6). This is the first example of a modifier gene in RDEB and has implications for its prognosis and possible new treatments.

Correction to: Antisense-Mediated Splice Modulation to Reframe Transcripts.

The original version of this book was published with the following errors: "2'MOE" have been corrected into "2'MOEPS" in figure.6 - Chapter 35, multiple typo errors in page numbers: 532, 533, 534, 537, 542, 548 and 549. These errors has been updated.

Antisense-Mediated Splice Modulation to Reframe Transcripts.

Numerous genetic disorders are caused by loss-of-function mutations that disrupt the open reading frame of the gene either by nonsense or by frameshift (insertion, deletion, indel, or splicing) mutations. Most of the time, the result is the absence of functional protein synthesis due to mRNA degradation by nonsense-mediated mRNA decay, or rapid degradation of a truncated protein. Antisense-based splicing modulation is a powerful tool that has the potential to treat genetic disorders by restoring the open reading frame through selective removal of the mutated exon, or by restoring correct splicing.We have developed this approach for a severe skin genetic disorder, recessive dystrophic epidermolysis bullosa, caused by mutations in the COL7A1 gene encoding type VII collagen. This gene is particularly suited for exon skipping approaches due to its unique genomic structure. It is composed of 118 exons, 83 of which are in frame. Moreover, these exons encode a single repetitive collagenous domain.Using this gene as an example, we describe general methods that demonstrate the feasibility and efficacy of the antisense-mediated exon skipping strategy to reframe transcripts.

APOBEC mutation drives early-onset squamous cell carcinomas in recessive dystrophic epidermolysis bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare inherited skin and mucous membrane fragility disorder complicated by early-onset, highly malignant cutaneous squamous cell carcinomas (SCCs). The molecular etiology of RDEB SCC, which arises at sites of sustained tissue damage, is unknown. We performed detailed molecular analysis using whole-exome, whole-genome, and RNA sequencing of 27 RDEB SCC tumors, including multiple tumors from the same patient and multiple regions from five individual tumors. We report that driver mutations were shared with spontaneous, ultraviolet (UV) light-induced cutaneous SCC (UV SCC) and head and neck SCC (HNSCC) and did not explain the early presentation or aggressive nature of RDEB SCC. Instead, endogenous mutation processes associated with apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like (APOBEC) deaminases dominated RDEB SCC. APOBEC mutation signatures were enhanced throughout RDEB SCC tumor evolution, relative to spontaneous UV SCC and HNSCC mutation profiles. Sixty-seven percent of RDEB SCC driver mutations was found to emerge as a result of APOBEC and other endogenous mutational processes previously associated with age, potentially explaining a >1000-fold increased incidence and the early onset of these SCCs. Human papillomavirus-negative basal and mesenchymal subtypes of HNSCC harbored enhanced APOBEC mutational signatures and transcriptomes similar to those of RDEB SCC, suggesting that APOBEC deaminases drive other subtypes of SCC. Collectively, these data establish specific mutagenic mechanisms associated with chronic tissue damage. Our findings reveal a cause for cancers arising at sites of persistent inflammation and identify potential therapeutic avenues to treat RDEB SCC.

A recessive form of hyper-IgE syndrome by disruption of ZNF341-dependent STAT3 transcription and activity.

Heterozygosity for human signal transducer and activator of transcription 3 (STAT3) dominant-negative (DN) mutations underlies an autosomal dominant form of hyper-immunoglobulin E syndrome (HIES). We describe patients with an autosomal recessive form of HIES due to loss-of-function mutations of a previously uncharacterized gene, ZNF341 ZNF341 is a transcription factor that resides in the nucleus, where it binds a specific DNA motif present in various genes, including the STAT3 promoter. The patients' cells have low basal levels of STAT3 mRNA and protein. The autoinduction of STAT3 production, activation, and function by STAT3-activating cytokines is strongly impaired. Like patients with STAT3 DN mutations, ZNF341-deficient patients lack T helper 17 (TH17) cells, have an excess of TH2 cells, and have low memory B cells due to the tight dependence of STAT3 activity on ZNF341 in lymphocytes. Their milder extra-hematopoietic manifestations and stronger inflammatory responses reflect the lower ZNF341 dependence of STAT3 activity in other cell types. Human ZNF341 is essential for the STAT3 transcription-dependent autoinduction and sustained activity of STAT3.

The Molecular Revolution in Cutaneous Biology: Emerging Landscape in Genomic Dermatology: New Mechanistic Ideas, Gene Editing, and Therapeutic Breakthroughs.

Stunning technological advances in genomics have led to spectacular breakthroughs in the understanding of the underlying defects, biological pathways and therapeutic targets of skin diseases leading to new therapeutic interventions. Next-generation sequencing has revolutionized the identification of disease-causing genes and has a profound impact in deciphering gene and protein signatures in rare and frequent skin diseases. Gene addition strategies have shown efficacy in junctional EB and in recessive dystrophic EB (RDEB). TALENs and Cripsr/Cas9 have emerged as highly efficient new tools to edit genomic sequences to creat new models and to correct or disrupt mutated genes to treat human diseases. Therapeutic approaches have not been limited to DNA modification and strategies at the mRNA, protein and cellular levels have also emerged, some of which have already proven clinical efficacy in RDEB. Improved understanding of the pathogenesis of skin disorders has led to the development of specific drugs or repurposing of existing medicines as in basal cell nevus syndrome, alopecia areata, melanoma and EB simplex. These discoveries pave the way for improved targeted personalized medicine for rare and frequent diseases. It is likely that a growing number of orphan skin diseases will benefit from combinatory new therapies in a near future.

Recessive dystrophic epidermolysis bullosa caused by COL7A1 hemizygosity and a missense mutation with complex effects on splicing.

Loss-of-function mutations in the gene encoding type VII collagen, COL7A1, are the molecular basis of the blistering skin disorder, recessive dystrophic epidermolysis bullosa (RDEB). COL7A1 maps to a region of the short arm of chromosome 3 that has been found to be deleted in many types of malignancies. We have characterized the first case of a large genomic deletion in chromosome 3p21.31 that removes COL7A1 entirely in an RDEB patient. This interstitial deletion spans 255 to 520 kb and encompasses 9 to 15 genes, but seems to have no pathological consequences other than RDEB. We show that the second, hemizygous allele of COL7A1 in this patient bears a base substitution within exon 94, c.7245G>A. This translates into an amino acid substitution, p.M2415I, and leads to a complex splicing abnormality that allows marginal levels of functional mRNA and protein to be synthesized. We propose that the leakiness of the splicing defect enables the partial rescue of collagen VII deficiency. This is consistent with the diagnosis of the moderately severe form of RDEB in the proband, at variance with the most severe form, RDEB Hallopeau-Siemens, that would arise from complete collagen VII deficiency.