Genotyping of unusual phenotypes of epidermolysis bullosa

This thesis aims to genotype unusual phenotypes of patients with the genetic blistering disorder epidermolysis bullosa (EB). The disease is accompanied by blisters and erosions of the skin and mucous membranes mostly starting at birth. Nowadays 10 genes coding for proteins important in epidermal-dermal adhesion have been described of which mutations lead to skin fragility. Besides, sequencing has led to a growing mutation-database. Despite extensive research, a part of the EB phenotypes is still not understood, especially the unexpected mild phenotypes. The goal of this thesis was to unravel the genetic background of these unusual phenotypes as they might harbour clues for future gene therapy. For instance, in revertant mosaicism of EB healthy skin areas are present where the deficient protein is re-expressed. This phenomenon is also sometimes referred to as ‘natural gene therapy’, a term immediately suggesting that understanding the reversion process could be useful in defining a good approach to EB therapy. In chapters 2 and 3 four patients in total are described who had such a mosaic pattern in their skin. All had distinct affected and unaffected skin patches without blistering tendency. A second interesting group of patients are those with a milder phenotype characterized by more localized blister formation than the phenotype usually observed in type XVII collagen-deficient patients. Chapters 4, 5 and 6 reveal that the presence of such a localized phenotype can be distinguished from the generalized variant on basis of immunofluorescence microscopy. Moreover, in the last experimental chapter, chapter 7, a completely new phenotype which we named lethal acantholytic EB is delineated. The genotyping of these phenotypes combined with subsequent RNA- and protein-analysis will deepen our knowledge and understanding of the functioning of wild-type and mutated protein.