New genetic diagnosis technique discovered
A team at Guy's Hospital has discovered a new technique which will revolutionise Pre-Implantation Genetic Diagnosis (PGD). The new procedure was presented at the annual conference of the European Society of Human Reproduction and Embryology in Prague.
PGD is used mostly by fertile couples at a high risk of passing on a severe genetic disorder. The couples involved undergo IVF and then the embryos are checked to see whether they contain the genetic fault or not. In this way couples can avoid passing on genetic diseases which could severely affect the quality of life of any child they bore.
The current procedure for PGD does not allow for much scope for testing different mutations of genetic disorders. The reason for this is that the mutation for each genetic disorder would have to be known and then a sample of DNA from one of the cells in the embryo tested to see if it contained the mutation. This means that embryos can only be tested for common mutations of genetic disorders (e.g. the delta F mutation for Cystic Fibrosis). There are however thousands of family specific mutations of different genetic disorders. It would take an enormous amount of time to catalogue all these mutations.
The new technique, called Pre-Implantation Genetic Haplotyping (PGH), changes all this. Without using any new techniques the team from Guy's has found a way to test for any mutation of a genetic disorder, completely changing how PGD is performed.
The procedure relies on there being a known carrier of the genetic disorder you wish to test for, which would generally be the case as only couples who are at high risk of passing on a specific genetic disorder would ever undergo PGD. A blood sample is taking from the family member and then a normal genetic test is carried out. Looking at each chromosome the genetic mutation can then be identified. If the mutation has link markers (parts of the gene which are passed on together and not separated in cell splitting) then the mutation can then be tracked. This is done by taking a single cell from the embryo, amplifying its DNA and then testing the DNA for the markers to see if the mutation has been inherited.
PGD is generally used by a small group of people due to the risks involved and the low success rate so this new leap forward will not hugely increase the amount of people using PGD. It does mean that thousands more mutations can be tested for without the need to know anything about the specific mutation and a larger amount of disorders in general can be tested. The procedure is much more accurate than current ones and also gives a lot more embryos for implantation as male embryos do not have to be discarded for X-related mutations.
PGH will dramatically change how the face of genetic diagnosis and will help many more families have healthy children. There have already been several pregnancies from the technique but we must wait to see how these turn out. If successful the technique is likely to be widely adopted.
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