Diagnostic dilemma of “sporadic” cases of dystrophic epidermolysis bullosa: a new dominant or mitis recessive mutation?

Abstract: Dystrophic forms of epidermolysis bullosa (DEB), characterized by mutations in the type VII collagen gene (COL7A1), are inherited either in an autosomal dominant or autosomal recessive fashion, and sporadic, de novo cases have also been reported. Clinically, the dominant forms (DDEB) can be indistinguishable from the mild, mitis forms of recessively inherited DEB (M-RDEB). This situation poses a dilemma in case of families with 1 mildly affected individual and clinically normal parents: Is it a new dominant or mitis recessive DEB? In this study we review 2 cases with mild DEB, the parents being clinically normal. One of the cases was shown to be a compound heterozygote for 2 silent missense mutations (R2063W/G2366S), thus being diagnosed as M-RDEB. The second case had a single glycine substitution mutation (G2079E) in COL7A1 and had therefore DDEB. These findings have implications for the genetic counseling of these families concerning the risk of recurrence of the disease in subsequent pregnancies in the present and future generations.     

A de novo glycine substitution mutation in the collagenous domain of COL7A1 in dominant dystrophic epidermolysis bullosa

Abstract Dystrophic epidermolysis bullosa (DEB) is a hereditary mechanobullous disorder characterized by fragility of the skin and mucous membrane due to abnormalities of anchoring fibrils. Both dominant and recessive DEB have been shown to be caused by mutations in COL7A1, the gene encoding type VII collagen which is the major component of anchoring fibrils. De novo mutation in dominant DEB is rare. In this study, we report a novel de novo glycine substitution mutation in COL7A1 in a Chinese female patient presenting with mild DEB. In search of the mutation, we scanned the entire COL7A1 using polymerase chain reaction (PCR) amplification of all exons of COL7A1, followed by heteroduplex analysis and direct sequencing of the PCR products that exhibited heteroduplex pattern. A G-to-A transition at nucleotide position 6082 within exon 73 of COL7A1was detected. The mutation converted a glycine to an arginine (G2028R) within the triple-helical domain of type VII collagen. It was confirmed that the mutation was present only in the proband. Haplotype analyses suggested that the case arose as a de novo occurrence of autosomal dominant DEB. Received: 1 September 1998 / Revised: 23 November 1999 / Accepted: 26 November 1999     

Three cases of de novo dominant dystrophic epidermolysis bullosa associated with the mutation G2043R in COL7A1

In the absence of a positive family history, it is often difficult to determine whether a single case of mild-to-moderately severe dystrophic epidermolysis bullosa (DEB) represents autosomal recessive or de novo dominant disease. Recent molecular analyses of the type VII collagen gene, COL7A1, have established that the vast majority of such cases are recessive in nature. Nevertheless, a small number of de novo dominant patients have been documented. In this report, we describe three further examples of de novo dominant disease. In each case the COL7A1 mutation comprised the same glycine substitution, G2043R. This mutation has previously been reported in both dominant DEB pedigrees and as a de novo phenomenon and is the most common COL7A1 mutation in dominant DEB throughout the world. These cases emphasize the importance of molecular analysis in providing accurate genetic counselling in this genodermatosis.     

COL7A1 Recessive mutations in two siblings with distinct subtypes of dystrophic epidermolysis bullosa: pruriginosa versus nails only

Dystrophic epidermolysis bullosa (DEB) is a rare, clinically heterogeneous, blistering genodermatosis inherited as either autosomal dominant or recessive trait. All DEB forms are caused by mutations in the COL7A1 gene, which encodes for type VII collagen, the major component of the anchoring fibrils ensuring epithelial-mesenchymal adhesion. Major determinants of clinical heterogeneity in DEB are COL7A1 mutation types and their consequences at mRNA and protein levels; nevertheless, siblings with the same genetic alterations can manifest highly variable clinical signs. Here, we report novel compound heterozygous recessive COL7A1 missense mutations in 2 siblings presenting different DEB clinical subtypes. Our findings document the rare occurrence of recessive inheritance for the nails only DEB variant and emphasize the role of acquired phenotype-modifying factors in DEB pruriginosa pathogenesis.     

Localised de novo dominant dystrophic epidermolysis bullosa

INTRODUCTION: Dystrophic epidermolysis bullosa is a hereditary heterogeneous blistering disease. Clinical examination and additional tests are not always sufficient to identify the subtype or mode of transmission. We describe a case of de novo dominant inherited dystrophic epidermolysis bullosa localised strictly to the knees. CASE REPORT: A 3-year-old boy presented symmetrical lesions on the anterior aspect of the knees since starting to walk. No nail, dental or mucous dystrophy was observed and the parents presented no clinical abnormalities. Optical microscopy, electron microscopy and immunofluorescence analysis suggested dystrophic epidermolysis bullosa. The genealogical tree allowed no distinction between the dominant de novo and mitis recessive forms. Genetic analysis identified a missense G 1776W mutation at exon 61 of gene COL 7A1 in the child's DNA but not the parents'. DISCUSSION: Dystrophic epidermolysis bullosa may present in generalized or localized forms and the disease may be inherited in either autosomal dominant or recessive mode. Genetic analysis shows mutations in COL 7A1. While the clinical features often allow different types to be distinguished when the parents do not have the disease (with the recessive forms being more severe), genetic analysis is essential to confirm the mode of inheritance. In the dominant forms, and more recently in recessive cases, glycine substitutions have been implicated, although the precise role of glycine substitution has yet to be clarified. Localised involvement of the skin alone, as seen in our case report, is very rare. CONCLUSION: Genetic analysis is important for genetic counselling and determination of risk of recurrence.     

Mutation analysis and characterization of COL7A1 mutations in dystrophic epidermolysis bullosa

Abstract:  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.     

A recurrent glycine substitution mutation, G2043R, in the type VII collagen gene (COL7A1) in dominant dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the type VII collagen gene (COL7A1). Nearly all cases of dominant DEB are caused by glycine substitution mutations occurring within the triple helical region of type VII collagen, and most of the mutations are unique to individual families. In this study, we identified a patient of Hispanic-Mexican origin with a mild form of DEB, which resulted from a de novo dominant glycine substitution, G2043R, in exon 73 of COL7A1. We also investigated a Scottish family with a three-generation pedigree of dominant DEB, in whom the same glycine to arginine substitution mutation was demonstrated. This particular mutation has also been detected previously in three other families with dominant DEB: one Italian, one Hungarian and one Norwegian. Given the widespread geographical distribution of this mutation and the demonstration of its occurrence as a de novo event, G2043R therefore represents the first example of a mutational hotspot in dominant DEB. Interestingly, although both the Mexican and Scottish families we studied had some clinical features in keeping with the Pasini form of the disorder, there was considerable interfamilial variability as well as intrafamilial diversity in the affected individuals.     

Identical glycine substitution mutations in type VII collagen may underlie both dominant and recessive forms of dystrophic epidermolysis bullosa

Autosomal dominant and recessive forms of dystrophic epidermolysis bullosa (DEB) result from mutations in the type VII collagen gene (COL7A1). Although paradigms have emerged for genotype/phenotype correlation in DEB, some pathogenic mutations in COL7A1, notably glycine substitutions within the type VII collagen triple helix, may lead to diagnostic difficulties, since certain glycine substitutions can result in either dominant or recessive mutant alleles. Delineation of glycine substitution mutations into two discrete groups, however, is made difficult by observations that, for some particular glycine substitutions in type VII collagen, the same mutation can result in both dominant and recessive disease. In this report we describe four further glycine missense mutations: p.Gly1483Asp, p.Gly1770Ser, p.Gly2213Arg and p.Gly2369Ser, which can lead to either dominant or recessive DEB, and which result in a spectrum of clinical abnormalities. We also identify a further 30 new glycine substitution mutations that cause either dominant or recessive DEB, but not both. In screening the COL7A1 gene for mutations in individuals with DEB our data highlight that delineation of glycine substitutions in type VII collagen has important implications for genetic counselling.     

Novel and recurrent COL7A1 mutation in a Polish population

Dystrophic Epidermolysis Bullosa (DEB) is a rare bullous genodermatosis caused by mutations in COL7A1, which encodes collagen type VII, the main component of anchoring fibrilis. DEB is inherited in an autosomal recessive and dominant manner, depending on the mutation type and localization. The aim of this study was to update the spectrum and frequency of COL7A1 mutations in a cohort of 42 Polish DEB patients. Using direct sequencing strategy we identified 25 different mutations, which gave us a detection rate of about 88%. In total, thirteen novel variants were identified, including three de novo mutations (p.G2680S, p.G2043R and p.Gly2064_Arg2069del). The panel of recessively inherited DEB causing recurrent mutations comprise of five variants: c.425A>G, c.682+1G>A, p.R2069C, p.W796X and, unreported before, c.7154delC, which accounts for about 59% of all mutated alleles in this group. In the dominant type of DEB, only p.G2043R was found to be recurrent and it was identified in 50% patients. Our results give further insight into the pathogenesis and epidemiology of DEB.     

Review of collagen VII sequence variants found in Australasian patients with dystrophic epidermolysis bullosa reveals nine novel COL7A1 variants

BACKGROUND: Dystrophic epidermolysis bullosa (DEB) is an inherited skin fragility disorder where blistering occurs in the sub-lamina densa zone at the level of anchoring fibrils (AFs) of the dermo-epidermal junction. Both autosomal dominant (DDEB) and recessive (RDEB) result from mutations in the type VII collagen gene (COL7A1). OBJECTIVE: The purpose of this study was to understand the genotype-phenotype correlation in Australian patients with DEB. METHODS: Skin biopsies from patients were processed for immunofluorescence mapping, the COL7A1 gene was screened for sequence variants. RESULTS: We report 14 Australian families with different forms of dystrophic epidermolysis bullosa (DEB) with 23 different COL7A1 allelic variants, nine of which were novel. Four cases of RDEB-HS combined two premature termination codon (PTC) variants and three other cases of RDEB-HS with combined PTC and spice-site or glycine substitution variants. G2043R, a de novo dominant variant, was also identified in this study. Four "silent" glycine substitutions were found in this study, G2775S, G1673R, G1338V and G2719A. EB17, with combined R2791W and G2210V variants, had a DDEB-Pasini phenotype, in contrast to two family members who had severe DDEB pruriginosa, with the same genotype. CONCLUSION: In this study, the RDEB variants included nonsense variants, splice site variants, internal deletions or insertions, "silent" glycine substitutions within the triple helix or N or C terminal ends of the triple helix and non-glycine missense variants within the triple helix domain. DDEB usually involves glycine substitutions within the triple helix of COL7A1 although other missense variants or splice-site alterations may underlie some cases.     

显性营养不良型大疱性表皮松解症COL7A1基因突变分析

Objective: Dystrophic epidermolysis bullosa is an autosomal dominant or recessive disorder caused by mutations in the gene encoding type Ⅶ collagen (COL7A1 gene). To detect the mutation of COL7A1 in a DEB family. Methods: We performed full exon sequencing on DNA of the proband, and verified the COL7A1 mutation site of her sister by Sanger sequencing. Results: The proband and her sister had the same COL7A1 genotype, and the point mutation on exon 86 was c.6761G>A (p.Gly2254Glu). Conclusion: A new mutation locus of DEB family COL7A1 gene is found, which has not been reported in China at present. © 2022 China Journal of Leprosy and Skin Diseases. All rights reserved.     

A recurrent frameshift mutation in exon 19 of the type VII collagen gene (COL7A1) in Mexican patients with recessive dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is an inherited blistering skin disorder caused by mutations in the type VII collagen gene (COL7A1). In this study, we determined the molecular basis of autosomal recessive DEB in a 19-year-old Hispanic Mexican woman by PCR amplification of genomic DNA, heteroduplex analysis, and automated sequencing of heteroduplex bandshifts. This approach revealed a homozygous frameshift mutation, 2470insG, in exon 19 of COL7A1 and resulted in attenuated basement membrane zone expression of type VII collagen, a reduced number of anchoring fibrils at the dermal-epidermal junction, and a sub-lamina densa level of blister formation. Clinically, the patient had widespread trauma-induced skin fragility and complete loss of the nails, but had less pseudosyndactyly of the fingers and toes and milder mucosal involvement compared to most patients with the generalized form of this genodermatosis. We also screened 7 other Hispanic-Mexican patients with recessive DEB, none of whom were known to be related to this individual, for the mutation 2470insG using heteroduplex analysis and direct sequencing and detected this mutation on 7/14 alleles. Haplotype analysis using intragenic COL7A1 and flanking polymorphisms and microsatellite markers revealed that all the mutant alleles had arisen on similar allelic backgrounds, consistent with propagation of a common Hispanic Mexican ancestral haplotype. In view of the high allelic frequency of the mutation 2470insG in the patients studied, we recommend initial screening for this mutation when attempting to identify the molecular pathology of recessive DEB in Hispanic Mexican patients.     

Squamous cell carcinoma in a family with dominant dystrophic epidermolysis bullosa: a molecular genetic study

Squamous cell carcinoma in a family with dominant dystrophic epidermolysis bullosa: a molecular genetic study Squamous cell carcinoma (SCC) is a frequent complication in the severe, recessively inherited forms of dystrophic epidermolysis bullosa (RDEB), however, only rarely reported in dominant DEB. Although the SCCs in RDEB are frequently well-differentiated by histopathology, they often have a poor prognosis due to multicentricity, rapid invasiveness, and development of distant metastases. In this study, we sought to determine the molecular basis of DDEB in a family with the unusual occurrence of SCCs. Specifically, a large DDEB family with 2 individuals being affected with SCC was analyzed for potential mutations in the type VII collagen gene (COL7A1) by heteroduplex scanning and direct nucleotide sequencing of PCR amplified segments of the gene. This mutation detection strategy disclosed a G-->A transition at nucleotide position 6,235 which resulted in substitution of a glycine by arginine within the collagenous region of COL7A1. This study establishes, for the first time, the molecular basis in a family with DDEB/SCC. Clinically, this study reemphasizes the importance of vigilance in surveying DEB patients, not only those with recessive but also with dominant inheritance, for SCC.     

The molecular basis of dystrophic epidermolysis bullosa in Mexico

BACKGROUND: Type VII collagen gene (COL7A1) mutations are the cause of dystrophic epidermolysis bullosa (DEB), but most mutations are specific to individual families, and there are limited data on the nature of COL7A1 mutations in certain ethnic populations. OBJECTIVE: To determine the molecular basis of DEB in Hispanic Mexican patients. METHODS: Patients were recruited through a newly established support group, Fundacion DEBRA Mexico. Molecular analysis was performed by polymerase chain reaction (PCR) of genomic DNA using COL7A1-specific primers, heteroduplex analysis, and direct nucleotide sequencing. RESULTS: Fifty-nine of a possible 67 COL7A1 mutations (88%) were identified in 36 affected individuals (31 recessive, five dominant) in 21 families. Recessive mutations included six frameshift mutations, four silent glycine substitutions, and two splice-site mutations. Dominant mutations comprised a de novo glycine substitution and an internal deletion. Conclusions This study establishes the molecular basis of DEB in a group of Mexican patients. Only two of the mutations have been identified previously in other ethnic groups; the remainder are specific to this population. These new data are helpful in facilitating the accurate diagnosis of DEB subtype, in improving genetic counseling, and in providing further insight into the pathophysiology of this mechanobullous disease.     

A glycine substitution in the COL7A1 gene causes mild RDEB in a Pakistani family

Pathogenic glycine substitutions can cause destabilization of the triple helix and a diverse range of heritable connective tissue disorders, dependent on the collagen gene in which the mutation occurs. Mutations in the type VII collagen gene (COL7A1) cause an inherited mechanobullous skin disease known as dystrophic epidermolysis bullosa (DEB). Typically, the dominant forms (DDEB) result from glycine substitutions within COL7A1, whereas other glycine mutations are 'silent' in the heterozygous state and produce disease only when they are homozygous. We studied three affected individuals from a large inbred Pakistani family with a history of skin fragility and scarring indicative of dystrophic EB. We identified a new glycine substitution within the collagenous region in exon 94 of the COL7A1 gene. This mutation, designated G2422V, resulted in a glycine (GGA) to valine (GTA) substitution presumably causing a destabilization of the protein by interrupting the Gly-X-Y repeats. This finding expands the allelic series of COL7A1 mutations underlying mild recessive dystrophic epidermolysis bullosa (RDEB) and sheds further light upon regions of the type VII collagen triple helix that are tolerant of heterozygous glycine substitutions.     

Identification of a glycine substitution and a splice site mutation in the type VII collagen gene in a proband with mitis recessive dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is a genodermatosis characterized by fragility of the skin and mucous membranes. Underlying mutations in the DEB phenotype have been detected in the gene encoding type VII collagen (COL7A1), both in the dominant and recessive forms of DEB. In this study, we searched for mutations in a proband with a mild form of DEB by PCR amplification of segments of COL7A1, followed by heteroduplex analysis. Examination of PCR fragments corresponding to exons 3–4 and exons 51–53 revealed heteroduplexes. Direct sequencing of the PCR fragment containing exon 3 revealed a previously reported A-to-G transition in the 5′ donor splice site of exon 3 in the proband and in the clinically unaffected father, while direct sequencing of the PCR fragment containing exon 53 revealed a novel glycine substitution G1652R in the proband and in the clinically unaffected mother. Patients with relatively mild DEB and no family history are frequently diagnosed as a de novo case of dominant DEB, although a mild case of RDEB cannot be excluded on the basis of clinical and ultrastructural examination. We proved this case to be a recessively inherited disease. This information had a profound impact on the genetic counselling, because if the disease of the patient were to have had a new dominant mutation, he would have been counselled that the risk of his offspring being affected was one in two, but he could be accurately counselled that the risk of this offspring being affected was as low as the general population. Received: 28 April 1997     

Exon 87 skipping of the COL7A1 gene in dominant dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is a rare, inherited, blistering disorder resulting from mutations in the COL7A1 gene, which encodes the anchoring fibrils, type VII collagen. We herein describe a further Japanese girl diagnosed with dominant DEB (DDEB). She had blisters sporadically and erosions healed with mild scarring and milia on the knees and pretibial regions. Severe pruritus was present at this time. Direct nucleotide sequencing of genomic DNA disclosed a heterozygous same splice-site mutation c.6900G>A in the COL7A1, which causes in-frame exon 87 skipping. So far, five different COL7A1 mutations leading to exon 87 skipping have been identified in rare forms of DEB: four DDEB pruriginosa and one pretibial DDEB. Therefore, a recent study suggested that exon 87 skipping in COL7A1 was related to the phenotype of DDEB pruriginosa. When she was 18 years old, however, the blister formation and pruritus markedly decreased. Therefore, her clinical symptoms were consistent to very mild DDEB but not to DDEB pruriginosa. Taken together, in-frame exon 87 skipping through c.6900G>A mutation may account for the mild skin features, rather than DDEB pruriginosa, in the present case.     

High frequency of the 425A-->G splice-site mutation and novel mutations of the COL7A1 gene in central Europe: significance for future mutation detection strategies in dystrophic epidermolysis bullosa

BACKGROUND: Mutations in the type VII collagen gene (COL7A1) are responsible for dominant and recessive forms of dystrophic epidermolysis bullosa (DEB). These mutations are usually specific for individual families; only a few cases of recurring mutations have been identified. OBJECTIVES: Forty-three unrelated Hungarian and German patients with different DEB phenotypes were screened for novel and recurrent COL7A1 mutations. METHODS: All patients were classified based on clinical and genetic findings, skin immunofluorescent antigen mapping, and electron microscopic studies. Mutation analysis was performed by amplification of genomic DNA with polymerase chain reaction using COL7A1-specific primers, heteroduplex analysis, and direct nucleotide sequencing. Restriction endonuclease digestion was used for family screening and mutation verification. Results In this group of patients, the splice-site mutation 425A-->G was observed frequently, in 11 of 86 alleles (12.8%), once in homozygous form and in nine cases in heterozygous form. One of 100 control alleles from clinically unaffected individuals also carried the mutation. We also identified three novel mutations: the 976-3C-->A splice-site mutation, and the 4929delT and 8441-15del20 deletions. CONCLUSIONS: High recurrence of the splice-site mutation 425A-->G in central European patients with DEB should be taken into account when designing COL7A1 mutation detection strategies. Reporting of three novel COL7A1 mutations in this study further emphasizes the molecular heterogeneity of DEB and provides more information for studies on genotype-phenotype correlations in different DEB subtypes.     

Expanding the COL7A1 mutation database: novel and recurrent mutations and unusual genotype-phenotype constellations in 41 patients with dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB), a heterogeneous hereditary skin disorder characterized by trauma-induced blistering and scarring, affects thousands of families worldwide. The clinical manifestations extend from minor nail dystrophy to severe life-threatening blistering, making early molecular diagnosis and prognostication of utmost importance for the affected families. DEB is caused by mutations in the COL7A1 gene encoding collagen VII in the skin. Molecular diagnostics and genotype-phenotype correlations in DEB remain complex owing to the gene structure, large variety of mutations, high rate of novel mutations, complex protein structure and assembly, and the heterogeneity of phenotypes. Here, we report an efficient strategy for COL7A1 mutation detection using direct automated DNA sequencing and implementation of software tools. With this approach, COL7A1 mutations of 41 DEB families were disclosed. Twenty-four mutations were novel and two recurrent. Elucidation of biological consequences of the mutations helped define disease mechanisms, but also revealed several unusual genotypic and/or phenotypic constellations, which impeded the diagnostics and prognostication. In addition, the studies disclosed a de novo mutation in recessive DEB and two new polymorphisms in the COL7A1 gene.     

De Novo COL7A1 mutation in a patient with trisomy 21: coexistence of dystrophic epidermolysis bullosa and Down syndrome

Background Down syndrome (DS) is the most common autosomal chromosomal disorder. Epidermolysis bullosa (EB) is a rare genodermatosis characterized by skin and mucous membrane fragility, with formation of blisters and erosions after minor trauma. Dystrophic EB (DEB) is inherited as an autosomal dominant (DDEB) or recessive (RDEB) trait. Both forms are caused by mutations in COL7A1, the gene coding for the type VII collagen. We report a patient affected by both conditions: DS and DDEB. Methods A patient with DS developed generalized blisters at the age of three months. Cytogenetic study was performed to confirm DS. Skin biopsies were examined with immunohistochemical and electron microscopy techniques to determine EB subtype. Genomic DNA was extracted from peripheral blood samples. COL7A1 mutations were screened by heteroduplex analysis using conformation‐sensitive gel electrophoresis and sequencing. Results Karyotype analysis revealed trisomy 21. Histological study agreed with a DEB diagnosis. Mutational analysis showed a heterozygous c.6127G>T mutation in COL7A1, which is compatible with DDEB. Parental study suggests that c.6127G>T arises as a de novo mutation. Conclusions This report demonstrates that EB can be associated with other common conditions and reports the case of a patient who suffered two de novo independent genetic conditions. It also contributes to expanding the knowledge and database of clinical and molecular aspects of DDEB.