Herlitz junctional epidermolysis bullosa

Junctional epidermolysis bullosa type Herlitz (JEB-H) is the autosomal recessively inherited, more severe variant of "lucidolytic" JEB. Characterized by generalized, extensive mucocutaneous blistering at birth and early lethality, this devastating condition is most often caused by homozygous null mutations in the genes LAMA3, LAMB3, or LAMC2, each encoding for 1 of the 3 chains of the heterotrimer laminin-332. The JEB-H subtype usually presents as a severe and clinically diverse variant of the EB group of mechanobullous genodermatoses. This article outlines the epidemiology, presentation, and diagnosis of JEB-H. Morbidity and mortality are high, necessitating optimized protocols for early (including prenatal) diagnosis and palliative care. Gene therapy remains the most promising perspective.

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.

A homozygous nonsense mutation in type XVII collagen gene (COL17A1) uncovers an alternatively spliced mRNA accounting for an unusually mild form of non-Herlitz junctional epidermolysis bullosa

In this study we describe six Italian patients presenting an unusually mild variant of non-Herlitz junctional epidermolysis bullosa associated with a reduced expression of type XVII collagen. All patients are homozygous for a novel nonsense mutation (R795X) within exon 33 of COL17A1 and show a common haplotype, attesting propagation of an ancestral allele within the Italian population. Analysis of patients' COL17A1 transcripts showed the presence of two mRNA species: a normal-sized mRNA carrying mutation R795X that undergoes rapid decay, and a transcript generated by in-frame skipping of exon 33. Patients keratinocytes were shown to synthesize minute amounts of type XVII collagen, which appeared correctly localized along the cutaneous basement membrane. We therefore suggest that the exon 33-deleted COL17A1 splice variant encodes for type XVII collagen molecules that maintain a functional role and account for the mild phenotype of our patients.

Implications of intragenic marker homozygosity and haplotype sharing in a rare autosomal recessive disorder: the example of the collagen type XVII (COL17A1) locus in generalised atrophic benign epidermolysis bullosa

Generalised atrophic benign epidermolysis bullosa (GABEB) is a form of junctional epidermolysis bullosa with a recessive mode of inheritance. The gene considered likely to be involved in this disease is COL17A1, since in the majority of GABEB patients the product of that gene, the 180-kD bullous pemphigoid antigen (BP180), is undetectable in skin. We have identified an intragenic COL17A1 microsatellite marker for which 83% of randomly selected control individuals are heterozygous. We observed homozygosity for different alleles of this marker in five out of six collagen type XVII-negative GABEB patients of different European descent. Five of the six COL17A1 alleles of three patients originating from the eastern part of the Netherlands were identical, as were the haplotypes including flanking markers. The 2342delG mutation was identified in all these five alleles. This confirms the expectation that due to genetic drift and hidden inbreeding for an autosomal recessive disorder with low gene frequency, such as collagen type XVII-negative GABEB, most disease alleles from a restricted geographical area will be "identical by descent". Our results demonstrate that involvement of a candidate gene can be confirmed by looking for identity by descent of highly informative intragenic markers.

Identification of the LAMB3 hotspot mutation R635X in a Hungarian case of Herlitz junctional epidermolysis bullosa

The Herlitz type of junctional epidermolysis bullosa (H-JEB) is a severe blistering disease affecting the skin and mucous membranes, which is usually lethal within the first year of life. The laminin 5 genes have been implicated as candidate genes for most patients with H-JEB. Recently, two hotspot mutations were delineated in the LAMB3 gene, known as R42X and R635X, and have been noted in over 50% of mutant LAMB3 alleles. Here, we present a case of H-JEB of Hungarian origin with a neonatal lethal outcome. Monoclonal antibody staining showed a lack of expression of the laminin 5 beta 3 chain, as a possible result of a mutation in one of the laminin 5 genes. Screening of the family identified the previously described mutation R635X in exon 14 of LAMB3 in each of the parents and one healthy sibling in the heterozygous form, while proband was homozygous for R635X, and the other sibling proved to be genotypically normal. These results underscore the widespread prevalence of R635X in H-JEB cases from around the world.

The prevalence of epidermolysis bullosa in Scotland

The prevalence of epidermolysis bullosa (EB) in Britain and most other countries is unknown. Patients suffering from the inherited forms of EB and living in Scotland have been traced. Two hundred and fifty-nine affected people from 76 families have been identified, of whom 211 were clinically assessed. One-third of these Scottish EB sufferers had never been seen by a dermatologist. In Lothian, where there appears to be a relatively high prevalence of EB, 75% of patients were unknown to their general practitioners. The point prevalence of all forms of EB at the outset of the study was 49.0 per million, comprising EB simplex 28.6 per million and dystrophic EB 20.4 per million. Extrapolation of accurate data available for the Lothians suggests that the point prevalence of all forms of EB in Scotland is in excess of these figures.

Premature termination codons are present on both alleles of the bullous pemphigoid antigen 2/type XVII collagen gene in five Austrian families with generalized atrophic benign epidermolysis bullosa

Patients with generalized atrophic benign epidermolysis bullosa (GABEB), an inherited subepidermal blistering disease, often have no immunologically detectable bullous pemphigoid antigen 2 (BPAG2) in their epidermal basement membrane. Recently, we analyzed the BPAG2 gene (GenBank no. M91669) in an Austrian family with GABEB and identified a homozygous deletion mutation, 4003delTC, that results in a downstream premature termination codon (PTC). This mutation has now been identified in additional descendants, suggesting transmission of this mutant allele through at least six generations. Screening of four other Austrian GABEB families revealed that affected members were homozygous for 4003delTC in two cases and heterozygous in two others. In the latter, mutational analysis identified two novel nonsense mutations, Q1403X and G803X, that were confirmed by restriction endonuclease digestions. Thus, PTCs on both alleles of BPAG2 are present in all of these GABEB families. Immunoprecipitation and northern blot studies of cultured keratinocytes from homozygous GABEB patients show that 4003delTC results in undetectable levels of BPAG2 protein and mRNA-findings consistent with the process of nonsense-mediated mRNA decay. Incubating keratinocytes with cycloheximide increased BPAG2 mRNA to a level detectable by northern analysis. When the latter was used in reverse transcription-PCR studies, the mutation was demonstrated, suggesting that cycloheximide may allow mutational analysis in cases where low transcript levels have previously thwarted RT-PCR studies. These findings account for the absence of BPAG2 in GABEB patients and attest to the importance of this protein in adhesion of epidermis to epidermal basement membrane.

Dental caries risk in hereditary epidermolysis bullosa

Epidermolysis bullosa (EB) is a clinically diverse group of conditions characterized by skin fragility and, in certain types, marked dental involvement. The purpose of this study was to determine the prevalence of dental caries in EB and control populations. Healthy individuals and participants from the Southern Clinical Center of the National EB Registry were examined with artificial light and a #23 dental explorer. Caries levels were evaluated by chi-square analysis, regression analyses, and ANOVA (P < 0.05 being significant). The study included 252 individuals with EB, aged 2.3-71 years, and 57 similarly aged controls. The prevalence of dental caries, scored as DMFS (decayed, missing, filled surfaces), was significantly higher in the junctional (mean = 58.6) and recessive dystrophic (mean = 37.6) EB types than controls (mean = 23.2). The simplex (mean = 25.6) and dominant dystrophic (mean = 21.6) EB groups had DMFS levels similar to the control group. Individuals with recessive dystrophic EB had the most severe oral blistering and scarring and did not have generalized enamel hypoplasia. In contrast, junctional EB always was associated with generalized enamel hypoplasia yet the intraoral blistering rarely involved scarring. This study shows that dental caries is increased in dystrophic and junctional EB compared with unaffected individuals or other EB types. While rampant caries appears related to the soft tissue and enamel involvement in these two EB types, other as yet unclear cofactors also must be involved.

Epidermolysis bullosa in Northern Ireland

Cases of epidermolysis bullosa (EB) diagnosed in Northern Ireland during a 23-year period (1962-84) were identified from dermatology clinic files, paediatric hospital notes and cases known by general practitioners. A total of 48 confirmed new cases of EB were diagnosed during the screening period. This involved 31 families, with identification of 36 further cases. The distribution of incident EB subtypes was: simplex 31 (65%), junctional 1 (2%), dystrophic 12 (25%) and acquisita 4 (8%). The incidence rate of new cases of EB diagnosed per year is 1.4/million and prevalence of all forms estimated at 32/million. The prevalence of simplex, junctional and dystrophic forms is 28, 0.7 and 3/million, respectively.