Gene chip technology will lead to quick and accurate genetic testing for cystic fibrosis
A single genetic test that is capable of detecting all mutations involved in the development of cystic fibrosis could be just a few years away, the 20th annual conference of the European Society of Human Reproduction and Embryology heard today (Monday 28 June).
Researchers at Monash University in Melbourne, Australia, have discovered that recently developed microarray (or gene chip) technology* can be used successfully to detect one of the commonest cystic fibrosis (CF) genetic mutations with 100% accuracy.
This means that, once the technology has been refined, gene chips could be used to detect all CF mutations in a single, quick and easy test that would produce almost immediate results. The analysis could be carried out on embryos during preimplantation genetic diagnosis (PGD), so that only healthy embryos would be transferred to the woman. The technology could be used during PGD for other genetic diseases too.
Ms Chelsea Salvado, a PhD student working with Professor Alan Trounson and Dr David Cram at the Institute of Reproduction and Development at Monash, explained: Currently there are many CF mutations diagnosed in the PGD laboratory, each requiring the development of a different diagnostic technique. However, the introduction of microarray technology would provide a uniform, single test, enabling PGD to be offered to couples presenting with different mutations without first having to undergo an extensive pre-clinical work-up. At present, this work-up can take anywhere between a week and six months to complete, depending on how easy it is to match the parental mutations with the markers used to prevent misdiagnosis.
Until now, the possibilities of using microarray technology in PGD had been largely unexplored. Ms Salvado set out to discover the diagnostic potential of gene chips by testing them on the ∆F508 mutation, which is the commonest CF mutation, accounting for 80% of all CF mutations worldwide.
She created gene chips that held information on the normal and diseased versions of ∆F508 and then tested them on DNA samples obtained from single cells and from groups of ten cells. Despite some initial problems with amplifying the samples successfully, meaning that an extra step had to be added to the process, the final results showed that the gene chips could diagnose the ∆F508 mutation with 100% accuracy in the 30 samples investigated.
This proved the concept that the ∆F508 mutation can be reliably and accurately diagnosed at the single cell level using microarray technology, said Ms Salvado. Further research is needed to improve the method, although many of the problems associated with the amplification of single cells would be reduced or eliminated if blastocyst biopsy (biopsy of 10 cells) was the method of choice in PGD.
There are over 1,000 mutations known to cause CF and their frequency varies between countries and communities. For example, in Australia 10 mutations are diagnosed routinely, all of which involve a mutation at a single point on the cystic fibrosis gene. Current work within our laboratory has shown that these point mutations may be detected with as much reliability and accuracy as the ?F508 mutation, said Ms Salvado.
It will be at least two to three years before this discovery starts to benefit patients. She said: This research needs to be enhanced by commercial microarray companies who have the capacity and the resources to develop more complex arrays with many different CF mutations. Further development of the method is critical to ensuring reliable microarray-based genetic diagnosis.
However, Ms Salvado believes that her research will have a significant impact in the future on couples carrying CF mutations. Microarray technology will lead to semi-automated genetic testing for both PGD and prenatal diagnosis, providing a rapid diagnosis, thus reducing the stress of couples waiting for a result. The introduction of microarray technology could lead to PGD being offered for all genetic diseases in the future.
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