PRE-IMPLANTATION GENETIC DIAGNOSIS

Pre-implantation Genetic Diagnosis (PGD) consists of a diagnosis of embryos resulting from IVF and discovering which ones are genetically normal. Following PGD those which have passed the test are transferred to the uterus to bring about a pregnancy.

This technique can be applied in a vast number of situations. Its most common use is for couples who have already had a child who is afflicted with an illness for which we know the gene which causes it. To prevent a new child from suffering from the same illness, this technique can be applied. It is also used for couples in which one or both of the parents has a genetic anomaly which can be transmitted to their children. We can also establish whether the embryos resulting from IVF carry the irregularity so that only genetically healthy embryos are used. Another use is for couples who have no difficulty in getting pregnant but for whom the pregnancy repeatedly ends in a miscarriage. In such cases, if following the appropriate tests no explanation for the miscarriages has been found, PGD may be used, given that the majority of this type of miscarriage has a genetic cause. Embryos with genetic problems and those which do not are diagnosed, thus minimising the risk of another miscarriage.

Finally, a more controversial use from the ethical point of view is for couples with a child who is afflicted with an illness which requires a transplant but one for which the donor can only be a sibling with an identical antigenic signature. In such cases IVF may be used for the couple in such a way that after the embryos undergo PGD we only transfer embryos with the desired antigenic signature. In this way the sibling who is born will be the ideal donor. As we have already said, the application of this technique has provoked a considerable ethical debate which continues to this day. There are detractors of this technique who appeal against the role of the child who is born with the "only" purpose of being a donor for his or her sibling, or who speak about degradation in the treatment of the embryo. But there are also those who defend the treatment who, in addition to putting themselves in the position of the parents, ask what better purpose there can be than to save the life of your sibling no sooner than you are born. On the other hand, in accordance with the new and recently passed Law on Assisted Reproduction this technique is perfectly regulated and is perfectly legal.

In theory Pre-implantation Genetic Diagnosis may also be used to diagnose the sex of the embryo so that only embryos of the desired sex are transferred. However, the selection of sex is forbidden in Spain, and may only be applied in cases of genetic illnesses which are transmitted in a specific sex and in which the gene which causes the illness cannot be diagnosed. It is only in such cases that we may carry out Pre-implantation Genetic Diagnosis to select the child’s sex.

PGD requires IVF beforehand in order to create several embryos which may then be handled in a laboratory. Three days after they are fertilised, when the embryo usually has around eight cells, a small hole is made in the surface of the embryo and one or two cells are extracted. These cells are genetically analysed after they have been extracted, just as might be done with white blood cells, the technique usually used to make a genetic diagnosis in an adult. Once we know which embryos are free of the genetic irregularity we are looking into, these are transferred to the uterus. It is important to point out that the child which will be born has no greater risk of any other irregularity because it has undergone this process in its embryonic phase.

The number of illnesses for which we know the genetic cause is constantly increasing. This is why Pre-implantation Genetic Diagnosis techniques are constantly increasing in importance in the clinic. For this reason, of the whole arsenal available to reproduction clinics, this technique is probably the one with the greatest scope for the future.