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Gene chips may speed diagnosis of genetic disease
A team of scientists from Monash University in Melbourne, Australia, have developed a new technique for genetic testing of embryos, based on microarray technology. Microarrays, also known as gene chips, are systems that enable the rapid and simultaneous analysis of thousands of DNA sequences. The researchers have found that they can be used for pre-implantation genetic diagnosis (PGD) of cystic fibrosis. Cystic fibrosis (CF), an inherited disease that affects the lungs and digestive system, is the most common life-shortening genetic disorder in the UK, with an overall birth prevalence of about 1 in 2500. Around 1 in 25 people carry a gene with a cystic fibrosis mutation; if a baby inherits one such gene from each parent then it will have the disease. The identification of embryos affected by and free from cystic fibrosis is one of the current uses of PGD.
The advantage of using microarrays is that multiple different mutations can be screened for at once. Although there is a single very common mutation associated with Cystic Fibrosis (the Delta F508 or ÄF508 mutation), there are many other less common mutations that can cause the disease, some very rare. Presently, parents may have to wait several weeks for embryos to be screened for a selection of the most common mutations. Ms Chelsea Salvado, a member of the Monash research team, is reported as having said: "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” (see BBC news report). Microarrays could also be used in prenatal testing for cystic fibrosis and other genetic disorders.
The technique, presented by the Australian researchers at the Annual Meeting of the European Society of Human Reproduction and Embryology in Berlin this week, requires the use of ten cells removed from embryos of between five and six days old, when the embryos have around 100 cells. At present most PGD tests are performed using single cells taken from three-day old embryos, which have eight cells in all, but the method of DNA amplification was not reliable for a single cell from these younger embryos.