Molecular Testing in Epidermolysis Bullosa

Detection of Novel Biallelic Causative Variants in COL7A1 Gene by Whole-Exome Sequencing, Resulting in Congenital Recessive Dystrophic Epidermolysis Bullosa in Three Unrelated Families

Background: Dystrophic Epidermolysis bullosa (DEB) is a rare, severe subtype of epidermolysis bullosa (EB), characterized by blisters and miliary rashes of the skin. Dystrophic EB (DEB) includes variants inherited both in an autosomal-dominant or autosomal-recessive manner. Recessive dystrophic EB (RDEB) is divided into many subtypes and prevails as a result of biallelic genetic mutations in COL7A1 gene encoding type VII collagen, a major stabilizing molecule of the dermo-epidermal junction. The blister formation is mainly due to the variable structural and functional impairment of anchoring fibrils in VII collagen (COLVII), responsible for the adhesion of the epidermis to the dermis. Method: Three Pakistani families (A, B and C) affected with congenital dystrophic epidermolysis bullosa were recruited in the present study. The whole-exome sequencing (WES) approach was utilized for the detection of the pathogenic sequence variants in probands. The segregation of these variants in other participants was confirmed by Sanger sequencing. Results: This study identified a novel missense variant c.7034G>A, p. Gly2345Asp in exon 91, a novel Frameshift mutation c.385del (p. His129MetfsTer18) in a homozygous form in exon no 3, and a previously known nonsense variation (c.1573 C>T; p. Arg525Ter) in exon 12 of COL7A1 gene in families A, B, and C, respectively, as causative mutations responsible for dystrophic epidermolysis bullosa in these families. Conclusion: Our study validates the involvement of the COL7A1 gene in the etiology of dystrophic epidermolysis bullosa. It further expands the COL7A1 gene mutation database and provides an additional scientific basis for diagnosis, genetic counseling, and prognosis purposes for EB patients.

A retrospective analysis of diagnostic testing in a large North American cohort of patients with epidermolysis bullosa

BACKGROUND

Accurate diagnosis of epidermolysis bullosa (EB) has significant implications for prognosis, management, and genetic counseling.

OBJECTIVE

To describe diagnostic testing patterns and assess diagnostic concordance of transmission electron microscopy (TEM), immunofluorescence mapping (IFM), and genetic analysis for EB.

METHODS

A retrospective cohort included patients enrolled in the Epidermolysis Bullosa Clinical Characterization and Outcomes Database from January 1, 2004, to July 8, 2019. Tests concluding the same EB type (EB simplex, junctional EB, dominant dystrophic EB, and recessive dystrophic EB) were considered concordant; those concluding different EB types were considered discordant; and those with nonspecific/nondefinitive results were equivocal.

RESULTS

A total of 970 diagnostic tests were conducted from 1984 to 2018 in 771 patients. Genetic analyses were performed chronologically later than IFM or TEM (P < .001). The likelihood of undergoing genetic analysis was greater for junctional EB and recessive dystrophic EB, and the same for dominant dystrophic EB as compared with EB simplex. TEM results in 163 patients were equivocal (55%), concordant (42%), and discordant (3%). IFM results in 185 patients were equivocal (54%), concordant (42%), and discordant (4%).

LIMITATIONS

Retrospective design.

CONCLUSIONS

Diagnostic testing has shifted in favor of genetic analysis. TEM and IFM frequently offer equivocal findings when compared to the specificity afforded by genetic analysis.

A unique LAMB3 splice-site mutation with founder effect from the Balkans causes lethal epidermolysis bullosa in several European countries

BACKGROUND

We have encountered repeated cases of recessive lethal generalized severe (Herlitz-type) junctional epidermolysis bullosa (JEB gen sev) in infants born to Hungarian Roma parents residing in a small region of Hungary.

OBJECTIVES

To identify the disease-causing mutation and to investigate the genetic background of its unique carrier group.

METHODS

The LAMB3 gene was analysed in peripheral-blood genomic DNA samples, and the pathological consequences of the lethal defect were confirmed by cutaneous LAMB3cDNA sequencing. A median joining haplotype network within the Y chromosome H1a-M82 haplogroup of individuals from the community was constructed, and LAMB3 single-nucleotide polymorphism (SNP) patterns were also determined.

RESULTS

An unconventional intronic splice-site mutation (LAMB3, c.1133-22G>A) was identified. Thirty of 64 voluntarily screened Roma from the closed community carried the mutation, but none of the 306 Roma from other regions of the country did. The age of the mutation was estimated to be 548 ± 222 years. Within the last year, more patients with JEB gen sev carrying the same unusual mutation have been identified in three unrelated families, all immigrants from the Balkans. Two were compound heterozygous newborns, in Germany and Italy, and one homozygous newborn died in France. Only the French family recognized their Roma background. LAMB3SNP haplotyping confirmed the link between the apparently unrelated Hungarian, German and Italian male cases, but could not verify the same background in the female newborn from France.

CONCLUSIONS

The estimated age of the mutation corresponds to the time period when Roma were wandering in the Balkans.

Ocular manifestations of genetic skin disorders

Genetic skin diseases, or genodermatoses, often have extracutaneous manifestations. Ocular manifestations in particular can have significant clinical implications, like blindness. Other manifestations, such as the corneal opacities that occur in X-linked ichthyosis, are asymptomatic but characteristic of a particular genodermatosis. Ophthalmologic examination can aid in diagnosis when characteristic findings are seen. The genodermatoses with ocular manifestations will be reviewed, but neurocutaneous, syndromes, genetic pigmentary disorders, and genetic metabolic diseases are not included because they are covered elsewhere in this issue.

Epidermolysis bullosa in animals: a review

Epidermolysis bullosa (EB) is a hereditary mechanobullous disease of animals and humans, characterized by an extreme fragility of the skin and mucous membranes. The main feature of EB in humans and animals is the formation of blisters and erosions in response to minor mechanical trauma. Epidermolysis bullosa is caused by mutations in the genes that code for structural proteins of the cytoskeleton of the basal keratinocytes or of the basement membrane zone. Based on the ultrastructural levels of tissue separation, EB is divided into the following three broad categories: epidermolysis bullosa simplex, junctional epidermolysis bullosa and dystrophic epidermolysis bullosa. Human types of EB are divided into several subtypes based on their ultrastructural changes and the mode of inheritance; subtypes are not fully established in animals. In humans, it is estimated that EB affects one in 17,000 live births; the frequency of EB in different animals species is not known. In all animal species, except in buffalo with epidermolysis bullosa simplex, multifocal ulcers are observed on the gums, hard and soft palates, mucosa of the lips, cheek mucosa and dorsum of the tongue. Dystrophic or absent nails, a frequent sign seen in human patients with EB, corresponds to the deformities and sloughing of the hooves in ungulates and to dystrophy or atrophy of the claws in dogs and cats. This review covers aspects of the molecular biology, diagnosis, classification, clinical signs and pathology of EB reported in animals.

Revisited diagnostics of hereditary epidermolysis bullosa

Hereditary epidermolysis bullosa is a big group of hereditary diseases with the main manifestations in the form of blisters on the skin and mucous coat after slight mechanical injuries. It is not always possible to diagnose this disease based on the clinical picture. The article discusses current laboratory diagnostics methods for hereditary epidermolysis bullosa including immunofluorescence antigen mapping (IFM), transmission electron microscopy (TEM) and genetic analysis (molecular or DNA diagnostics) as well as their advantages and disadvantages. TEM determines the micro splitting level and nature of ultrafine changes in the area of the dermoepidermal junction; at the same time, such tests need special expensive equipment. Substantial experience is also needed to analyze the resulting submicroscopic images. IFM determines whether expression of the affected protein related to the disease development is reduced or absent; however, invalid (false positive or false negative) results can be obtained in patients with the reduced expression of the affected protein. Genetic analysis plays a key role for prenatal diagnostics. Therefore, to make an exact diagnosis of hereditary epidermolysis bullosa, it is expedient to apply IFM, TEM and genetic analysis. The need to set an exact diagnosis of the disease is related to the fact that the promising treatment methods being currently developed are aimed at treating patients with certain forms of the disease.

The genetics of skin fragility

Genetic skin fragility manifests with diminished resistance of the skin and mucous membranes to external mechanical forces and with skin blistering, erosions, and painful wounds as clinical features. Skin fragility disorders, collectively called epidermolysis bullosa, are caused by mutations in 18 distinct genes that encode proteins involved in epidermal integrity and dermal-epidermal adhesion. The genetic spectrum, along with environmental and genetic modifiers, creates a large number of clinical phenotypes, spanning from minor localized lesions to severe generalized blistering, secondary skin cancer, or early demise resulting from extensive loss of the epidermis. Laboratory investigations of skin fragility have greatly augmented our understanding of genotype-phenotype correlations in epidermolysis bullosa and have also advanced skin biology in general. Current translational research concentrates on the development of biologically valid treatments with therapeutic genes, cells, proteins, or small-molecule compounds in preclinical settings or human pilot trials.

Diagnosing epidermolysis bullosa type and subtype in infancy using immunofluorescence microscopy: the Stanford experience

The natural history of inherited epidermolysis bullosa (EB) varies significantly across subtypes. When confronted with an infant suspected to have EB, rapidly determining the type and subtype is critical in counselling families accurately about the infant's diagnosis and prognosis. Although transmission electron microscopy (TEM) has been considered the criterion standard for EB diagnosis, immunofluorescence microscopy (IFM) using monoclonal antibodies (mAbs) to EB-specific basement membrane zone proteins has several advantages, but few studies have evaluated the diagnostic utility of IFM. We sought to evaluate the clinical utility of IFM using an expanded panel of EB-specific mAbs. This was a retrospective review of pathology reports from infants younger < 1 year old with suspected EB primarily analyzed with IFM by the Stanford Dermatopathology service. Seventy-seven cases were identified for analysis, of which 20 were suboptimal for IFM analysis. Fifty-five cases were diagnosed with EB and classified as follows: EB simplex (n = 5), junctional EB (n = 31), dystrophic EB (n = 19). TEM was available in 36 of 55 cases (65%). IFM with an expanded panel of EB-specific mAbs should be considered the first-line diagnostic test to evaluate infants with clinically suspected EB.