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  10. Diagnosis of genetic defects (Preimplantation Diagnosis)

Preimplantation Diagnosis
IVF & GENETICS is undoubtedly a world class unit and a leader in both clinical treatment and research. One of the most remarkable advances has been in the field of the diagnosis of genetic diseases in embryos.

Preimplantation diagnosis, to give it its proper title, has already helped some of our couples who are at risk of having a baby with the so-called sex linked disorders. These severe illnesses, often fatal, usually only affect children of one sex (commonly boys) and include haemophilia, certain types of severe mental and physical retardation and Duchenne muscular dystrophy. We are progressing rapidly and are now able to screen for several defects which are not sex-linked, including thalassaemia - a disease which causes the death of over 250,000 babies each year around the world. We are extending this work to help women at risk of having a baby with a chromosomal disorder, such as Down's syndrome, or those who have chromosomal abnormalities causing risks of recurrent miscarriages, and the future looks very promising. The work is also being extended to reduce the genetic risks of cancer in certain families, where there is a 90% probability of a given child in that family developing such cancers as breast, bowel or brain cancer in young adulthood.

The preimplantation diagnosis technique involves stimulating the woman's ovaries to produce many eggs, just as we do for IVF. The nature of genetic disease usually means that some eggs will carry the defect, but others will be normal. The eggs are collected just as they are during IVF and approximately 48 - 72 hours after fertilization, one cell is removed from each embryo, under a microscope. At this stage of development, the embryo is quite invisible and the piece we remove even smaller. You can imagine that the surgery to remove one cell without damaging the rest of the embryo is quite delicate and needs very sophisticated equipment. The cell that is removed is then examined at molecular level. In the case of gene disorders, DNA (which is the basic genetic code) is extracted from the cell and tests are run to see if the defective gene is present. If the embryo is free of the specific disease from which the family are at the risk, it may then be suitable for transfer. Currently, this extremely difficult technology is at the cutting edge of the latest medical research.

If you are a patient attending the clinic for preimplantation diagnosis, a very thorough explanation of all that is involved will certainly be given to you and there will be plenty of time to discuss the implications of this treatment with various members of our team. It is now clear that changes in hormonal stimulation in some cases, or altering culture conditions in many others, can make a major difference in the way embryos develop. Preimplantation diagnosis provides one of the biggest hopes for improving routine IVF treatment at the present time.

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