LAMB3 mutations in generalized atrophic benign epidermolysis bullosa: Consequences at the mRNA and protein levels

Junctional epidermolysis bullosa: genotype-phenotype correlations

Junctional epidermolysis bullosa most commonly results from mutations in theLAMA3, LAMB3, LAMC2, COL17A1, ITGA6 and ITGB4genes. Junctional epidermolysis bullosa is characterized by clinical heterogeneity. To date, scientific findings allow to evaluate correlations between the severity of clinical manifestations and genetic defects underlying in the development of the disease. A systematic literature search was performed using PubMed and RSCI, and keywords including junctional epidermolysis bullosa, laminin 332, collagen XVII, 64 integrin. The review includes description of clinical findings of junctional epidermolysis bullosa, mutation location and types, its impact on protein production and functions. To evaluate the impact of gene mutation on protein functions, this review explores the structure and functions of lamina lucida components, including laminin 332, collagen XVII and 64 integrin, which are frequently associated with the development of junctional epidermolysis bullosa. The correlation between severe types of junctional epidermolysis bullosa and mutations resulting in premature stop codon generation and complete absence of protein expression has been described. Although, genotype-phenotype correlations should be analyzed carefully due to mechanisms which enable to improve protein expression.

A novel homozygous point mutation in the COL17A1 gene in a Chinese family with generalized atrophic benign epidermolysis bullosa

We describe a Chinese family with generalized atrophic benign epidermolysis bullosa (GABEB), a non-lethal variant of junctional epidermolysis bullosa. The proband was an offspring of consanguineous parents, had generalized blisters since birth and developed severe alopecia during early childhood. Ultrastructural examination of the proband's skin revealed fissures in the lamina lucida. Immunofluorescence assays using a monoclonal antibody recognizing the extracellular domain of the 180 kDa bullous pemphigoid antigen (BPAG2) showed loss of fluorescent signal in the basal membrane zone of the skin. DNA sequencing revealed a homozygous C-to-G transversion at nucleotide position 899 in exon 11 of the COL17A1 gene, which encodes BPAG2. This mutation results in serine to cysteine at position 265, which is located in a highly conserved region of the intracellular domain of BPAG2. We showed that the proband's father was heterozygous for this mutation. In addition, we found a novel polymorphic substitution of C-to-G at nucleotide position 798 in exon 10 of the COL17A1 gene, which results in an I233M change in BPAG2 and is a common polymorphic allele in a limited Chinese population.

E210K mutation in the gene encoding the beta3 chain of laminin-5 (LAMB3) is predictive of a phenotype of generalized atrophic benign epidermolysis bullosa

Pathogenetic mutations in the genes encoding the hemidesmosome-anchoring filament complex proteins, laminin-5 and the 180 kDa bullous pemphigoid antigen, have been identified in patients with the inherited mechanobullous disease, junctional epidermolysis bullosa (EB). Furthermore, there is some evidence to suggest that precise definition of the nature of mutations in these genes may correlate to specific phenotypes of disease. We report three junctional EB patients who carry an identical missense mutation, E210K, on one allele of the gene encoding the beta3 subunit chain of laminin-5 (LAMB3) in addition to different nonsense mutations on the second allele. Two of the patients are adults and display a specific phenotype of non-lethal junctional EB known as generalized atrophic benign EB, which is associated with trauma-induced blisters, nail dystrophy and alopecia. As the third patient is a young child with fewer features of this subtype to date, identification of E210K in combination with a nonsense LAMB3 mutation may be predictive of the subsequent development of a generalized atrophic benign EB phenotype both in this child and in other junctional EB patients with the E210K mutation. Identification of this particular mutation has important implications for clinical management and counselling.