Denaturing HPLC-based approach for detection of COL7A1 gene mutations causing dystrophic epidermolysis bullosa

Dominant pretibial dystrophic epidermolysis bullosa in an Italian family

We describe a case of pretibial dystrophic epidermolysis bullosa in a 5-year-old girl, her mother, and maternal great aunt. All subjects had trauma-induced blisters and erosions, with scarring, on the knees and lower legs, and nail dystrophy of variable severity. Genetic analysis in all three patients showed a 6849del18 mutation in the COL7A1 gene, causing the production of shortened collagen VII polypeptides and resulting in a mild phenotype, with localized acral blisters and nail involvement.

Recessive bullous dermolysis of the newborn in preterm siblings with a missense mutation in type VII collagen

Bullous dermolysis of the newborn is a dominant or recessive inherited subtype of dystrophic epidermolysis bullosa characterized by the tendency to spontaneously stop blistering within the first months of life. Here we report two siblings with bullous dermolysis of the newborn who were born prematurely and have a novel recessive mutation, p.Pro2259Leu, in the triple helix domain of type VII collagen. We discuss the possible relationship between genotype and prematurity and clinical manifestations in these patients.

Epidermolysis bullosa care in Italy

Epidermolysis bullosa (EB) has officially been recognized as a rare disease in Italy. Regional reference centers for EB have been created during the past years. This article discusses the clinical services and coordinated multidisciplinary management of EB in Italy.

Design and validation of a conformation-sensitive capillary electrophoresis system for mutation identification of the COL7A1 gene with automated peak comparison

Dystrophic epidermolysis bullosa is a heritable skin disease in which blisters occur because of a defect in type VII collagen resulting from mutations in the COL7A1 gene that is composed of 118 exons. Although a few mutations are specific to certain populations owing to founder effects, and although a few mutational hotspots exist, most mutations are unique to families and can be found scattered throughout the entire COL7A1 gene. This emphasizes the need for a sensitive, reliable, and efficient mutation scanning technique. Therefore, we developed a conformation-sensitive capillary electrophoresis (CSCE) system for COL7A1 mutation scanning. Here we report on the design and validation of this system. The CSCE technique is based on the principle of heteroduplex formation when polymerase chain reaction-amplified DNA fragments containing heterozygous sequence changes are slowly reannealed. These fluorescently labeled fragments have different migration characteristics and can be detected on a multi-capillary automated sequencer. Validation was performed by analysis of 29 known COL7A1 sequence changes, covering 33% of amplicons. After optimization of the conditions, all 29 sequence changes were detected by the CSCE system, irrespective of length or CG-content of amplicons and position of sequence changes, reflecting an analytical sensitivity of 90.2-100% (95% confidence interval). We conclude that this CSCE system is a rapid, reliable, cost-effective, and highly sensitive way of mutation scanning for COL7A1 in a molecular genetics service laboratory.

Dystrophic epidermolysis bullosa phenotypes in a large consanguineous Tunisian family

BACKGROUND

Dystrophic epidermolysis bullosa (DEB) is a clinically heterogeneous blistering disorder of the skin and mucous membranes. DEB is caused by mutations in the COL7A1 gene encoding type VII collagen, the major component of anchoring fibrils. On the basis of the mode of inheritance and the clinical manifestations, DEB is classified into two major subtypes: one dominant (DDEB) and one recessive (RDEB).

OBJECTIVE

We report, here, clinical, histological and genetic investigation of a large Tunisian family presenting with a wide range of clinical manifestations of DEB and a pedigree suggestive for a pseudodominant pattern of inheritance of a recessive mutation.

METHODS

Indirect immunofluorescence (IF) with the antibody LH7:2 against collagen VII and electron microscopy (EM) analyses were performed. The members of the family were genotyped with five markers flanking COL7A1, and screening for the deleterious mutation by DHPLC and direct sequencing.

RESULTS

The family presented four pretibial DEB patients and one generalized RDEB. Molecular investigation showed that all family members, unaffected and affected by the pretibial form, were heterozygous for the c.7178delT mutation, except for the member with the generalized form who was homozygous. IF showed that heterozygous individuals, independently of their clinical status, have a slightly reduced staining, and the homozygous individual with generalized DEB has markedly reduced staining at the dermal-epidermal junction.

CONCLUSION

These results are suggestive for an autosomal semidominant model of inheritance with incomplete penetrance and variable expression for the identified mutation. No genotype phenotype correlation was observed suggesting the existence of other genetic determinants influencing dermo-epidermal junction cohesion.

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.

Herlitz junctional epidermolysis bullosa: laminin-5 mutational profile and carrier frequency in the Italian population

BACKGROUND

Herlitz junctional epidermolysis bullosa (HJEB; MIM 226700) is a rare epithelial adhesion disorder caused by null mutations in any of the three genes encoding the alpha3, beta3 and gamma2 chains of laminin-5, and is mainly characterized by extensive mucocutaneous blistering, recurrent infections and early lethality.

OBJECTIVES

To perform immunoepitope mapping, electron microscopy and molecular analysis of five Italian patients with HJEB in order to complete the clinical and molecular characterization of patients with HJEB collected in the Italian Registry of hereditary epidermolysis bullosa (IRHEB) and to calculate the HJEB carrier frequency in this population.

METHODS

Skin biopsies from perilesional skin of all patients were employed for immunoepitope mapping and electron microscopy examination. Blood genomic DNA was used for mutation analysis in the LAMA3, LAMB3 and LAMC2 genes by heteroduplex scanning, preceded by a search for Italian recurrent mutations. Carrier frequency calculation was performed assuming Hardy-Weinberg equilibrium.

RESULTS

Two novel mutations in the LAMA3 (p.R782X) and LAMC2 (c.3235delA) genes, as well as three known and recurrent mutations in the LAMB3 (c.31insC and p.R81X) and LAMC2 (p.Y355X) genes were identified. Based on disease incidence reported in the IRHEB and the prevalence of mutations in each laminin-5 gene, the population carrier risk for HJEB was calculated to be one in 375.

CONCLUSIONS

Our delineation of a laminin-5 mutational spectrum in the general Italian population provides a solid basis for expedited diagnosis, accurate genetic counselling and DNA-based prenatal testing for Italian families at risk for recurrence of HJEB.

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.

Dystrophic epidermolysis bullosa pruriginosa in Italy: clinical and molecular characterization

Dystrophic epidermolysis bullosa (DEB) pruriginosa (DEB-Pr) is a rare variant of DEB due to COL7A1 dominant and recessive mutations, which is characterized by severe itching and lichenoid or nodular prurigo-like lesions, mainly involving the extremities. Less than 30 patients have been described showing variable disease expression, and frequently, delayed age of onset. We report the clinical and molecular characterization of seven Italian DEB patients, three affected with recessive DEB-Pr and four with dominant DEB-Pr. In all the patients, the signs were typical of a mild DEB phenotype, until the onset of pruritus, which was followed by worsening of the clinical picture, with appearance of the distinctive lichenified lesions of DEB-Pr. Nine mutations were found in the COL7A1 gene, three of which were novel and one was de novo. DEB-Pr patients with either dominant or recessive mutations were shown to synthesize a normal or variably reduced amount of type VII collagen, which was correctly deposited at the dermal-epidermal junction. Since six of these mutations have been reported in DEB patients in the absence of intense pruritus, these data implicate a role of yet unidentified phenotype-modifying factors in the pathogenesis of DEB-Pr.

Genetics of HUS: the impact of MCP, CFH, and IF mutations on clinical presentation, response to treatment, and outcome

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy with manifestations of hemolytic anemia, thrombocytopenia, and renal impairment. Genetic studies have shown that mutations in complement regulatory proteins predispose to non-Shiga toxin-associated HUS (non-Stx-HUS). We undertook genetic analysis on membrane cofactor protein (MCP), complement factor H (CFH), and factor I (IF) in 156 patients with non-Stx-HUS. Fourteen, 11, and 5 new mutational events were found in MCP, CFH, and IF, respectively. Mutation frequencies were 12.8%, 30.1%, and 4.5% for MCP, CFH, and IF, respectively. MCP mutations resulted in either reduced protein expression or impaired C3b binding capability. MCP-mutated patients had a better prognosis than CFH-mutated and nonmutated patients. In MCP-mutated patients, plasma treatment did not impact the outcome significantly: remission was achieved in around 90% of both plasma-treated and plasma-untreated acute episodes. Kidney transplantation outcome was favorable in patients with MCP mutations, whereas the outcome was poor in patients with CFH and IF mutations due to disease recurrence. This study documents that the presentation, the response to therapy, and the outcome of the disease are influenced by the genotype. Hopefully this will translate into improved management and therapy of patients and will provide the way to design tailored treatments.