Generalized atrophic benign epidermolysis bullosa

Abstract

Junctional EB was once considered a uniformly fetal autosomal recessive skin disease. One of the first and best characterized forms of generalized JEB that has a more favorable prognosis was GABEB. Since its initial description in 1976, many additional cases have been compiled, all sharing the features of chronic blistering from birth, nail dystrophy, hair loss, and abnormal teeth. In addition, some patients have large melanocytic nevi that form at sites of prior blisters. The first clues as to the protein defective in these patients was provided by immunofluorescence microscopy studies, which showed absent or decreased expression of type XVII collagen in these patient's epidermal BM. This protein was a promising candidate because it is located in the ultrastructural plane where blisters from in patients with GABEB. It is also the same hemidesmosomal protein against which antibodies are directed in patients with autoimmune blistering diseases: bullous, gestational, and cicatricial pemphigoid. The demonstration of decreased expression of type XVII collagen in patients with GABEB pointed the way to a crucial distinction that could not be based on clinical and histologic findings--that of discriminating infants with GABEB from those with the lethal Herlitz variant of JEB. These two diseases may be differentiated because decreased expression of type XVII collagen is found exclusively in GABEB, whereas decreased expression of laminin 5 is most likely associated with Herlitz JEB. The molecular basis of GABEB has been determined. The immunofluorescence microscopy studies mentioned above directed mutation studies to the COL17A1 gene. Several mutations in COL17A1 have been described in patients with GABEB, almost all of which result in a PTC. As a consequence of the PTC, mutant COL17A1 transcripts are rapidly degraded by nonsense-mediated mRNA decay, blocking production of type XVII collagen from the mutant allele. Heterozygous carriers of the mutation are thus rendered untouched by the mutation. In the homozygous state, however, this results in the absence of this vital adhesion protein, leading to chronic blistering and skin fragility observed in these patients. These studies also significantly increase our knowledge about the normal functions of type XVII collagen. The fact that patients deficient in type XVII collagen have fragile skin attests to the role of this protein in the adhesion of basal keratinocytes to epidermal BM. The severity of GABEB, however, is much less than that observed in patients with a complete deficiency of laminin 5, suggesting that type XVII collagen functions cooperatively with other hemidesmosomal proteins in promoting adhesion. Studies using GABEB keratinocytes will help characterize these kinds of interactions. The ultimate prospect of mutation analysis in these patients is the hope of correcting their genetic defect and curing their disease. Until then, the physician plays an important role in making the diagnosis, providing general supportive skin care, advising avoidance of trauma, treating infections, and supporting the patient's psychosocial development. Further studies of patients with GABEB will lead to new therapeutic approaches, as well as reveal additional complex functions of type XVII collagen not only in skin, but also in hair, teeth, and nails.