| SUMMARY OF RESEARCH BEING UNDERTAKEN
Epidermolysis
Bullosa is a set of genetically inherited conditions affecting 1 in at least 17,000 of the
population. A fault in a gene causes the skin to be extremely fragile. The layers of the
skin do not adhere properly and painful widespread blisters occur very easily. Recessive
dystrophic EB (RDEB) is one of the most severe forms with an estimated prevalence of 1 in
35,000.
Patients affected by DEB suffer from loss of adhesion between the epidermis (outer
layer of the skin) and the dermis (inner layer). This results in severe blistering of the
skin and mucosa after mild trauma and is evident from birth. The extreme fragility of the
skin results in traumatic blistering, wounds and scarring. These lead to increasing
disfigurement, deformity and disability.
DEB is caused by abnormalities in the type VII collagen gene (COL7A1) encoding
anchoring fibrils which form attachment structures playing a key role in the adhesion of
the epidermis to the dermis. The majority of patients do not produce type VII collagen
protein because they have inherited a deficient COL7A1 gene from each of their parents.
The identification of COL7A1 as the defective gene in 1991 has allowed searches for
mutations in patients and their family members to be carried out.
Identification of the COL7A1 defect in a given family has important implications for
genetic counselling eg the detection of carriers, assessment of the mode of inheritance
and early prenatal diagnosis (11 weeks of gestation) in affected families. It is also the
first step towards genetic correction of the defect, since it enables the presence of a
normal copy of the gene, following gene transfer, to be distinguished from the mutated
copy.
Summary of Research
COL7A1 is a complex gene comprising 118 exons, the
exhaustive screening of which remains a challenging task for each patient. Dr
Hovnanian’s group have observed that the mutations screening remained negative in a
significant number of patients after complete screening of the COL7A1 gene. This may be
due to the sensitivity of the mutation detection method and/or to the nature and position
of the mutation within the gene. This research seeks to overcome this problem by screening
the shortened version of the gene (COL7A1cDNA) which contains only the genetic information
coding for the type VII collagen protein.
In addition to being 3.7 times smaller (still 9200 letters of the genetic code) than
the COL7A1 gene (32000 letters), the COL7A1cDNA will greatly facilitate the detection of
mutations altering the "splicing" of the
COL7A1 gene. This approach will require growth of epidermal cells (keratinocytes) from
a 5mm skin biopsy taken under local anaesthetic from each patient. This new approach will
provide a powerful mutation screening strategy which is anticipated to result in the rapid
identification of the majority of the defects in DEB patients.
The second part of the project aims to develop genetic correction using the
"shortened" version of the COL7A1 gene (COL7A1cDNA). Indeed, one copy of the
normal COL7A1 gene or cDNA is sufficient to correct the condition, as indicated by the
observation that parents who produce only 50% of the normal amount of the type VII
collagen protein do not have EB. The aim is to initially isolate the entire COL7A1cDNA
molecule from normal skin. This will be a labour intensive work considering the size of
this "shortened" version of COL7A1. The aim then is to check the integrity of
this molecule assembled from smaller fragments. It will then be necessary to verify that
it encodes a normal type V11 collagen protein. Once it has been shown that it produces
normal type VII in epidermal cells, the plan is to use different systems to deliver this
normal copy of the COL7A1cDNA into chromosomes of patient’s cells. Integration of
this molecule into the patients cells genome should allow type VII collagen to be
permanently re-expressed and normal anchoring fibrils to be formed. This will lead to the
development of a completely new approach to treat the condition using patient’s
epidermal skin grafts grown in culture and producing normal type VII collagen. |
