Genetic Investigation on Embryos
| | For the difference between diagnosis and screening: For more information regarding saviour babies click on HLA-typing |
|
PGD is only performed to avoid possible hereditary conditions. |
|
|
|
|
In IVF these days, it is possible to detect abnormalities very early on. After fertilization, embryos can be examined and tested before they are 'implanted' or placed in the uterus, hence the name of the procedure: 'Pre-implantation Genetic Screening' (PGS) or 'Pre-implantation Genetic diagnosis' (PGD).
The very first PGD was carried out in the UK in 1990. Since then, it has been implemented worldwide in specialist centres.
Since 1993 it has been performed in our centre, for which we work very closely together with the CMG. The technique is offered to couples who run the risk of having genetically impaired embryos due to age or hereditary conditions. Thanks to the existence of PGD, patients who may otherwise miscarry, can have their embryos examined and only healthy ones replaced at transfer.
In the lab
After fertilization via ICSI, the moment is awaited when the embryos consist of eight cells (day three). Then, two cells are carefully removed from each embryo and genetically analysed:
- the cells are screened (PGS) via FISH-analysis if a change in chromosome structure or number is sought;
- a specific diagnosis is made (PGD) if the hereditary cause of the condition is known. In other words, is this gene a carrier of the condition which we are looking for?
- the result is known on day five. The embryos with no abnormalities can be considered for embryo transfer. If there are more than required, the surplus embryos (quality permitting) can be frozen and stored for later use in further treatments. The abnormal embryos will not be used, unless you release them to us for the purposes of scientific research.
For whom is it performed?
A couple comes into consideration for PGS or PGD if there is an increased risk that their child may suffer from a hereditary condition. It is only performed upon embryos which have been created by the ICSI technique, in order to be able to work with as many good quality embryos as possible.
during you treatment, you will be counselled by a clinician and a psychologist from the CMG. The making of an accurate diagnosis from a single embryonic cell is generally only possible if thorough investigations are performed beforehand. Every sickness requires an apart and often individualized test. This is the reason why there is often a long waiting list (up to a year) for this procedure.
A good number of hereditary diseases are detectable by the use of PGS/PGD. We list a few of the most important ones here.
cystic fibrosis (mucoviscidosis)
This condition leads to an abnormally high production of mucus in the lungs, which can cause countless infections. About 1 in 2000 children suffer from this serious, hereditory disease and 1 in 22 people are carriers. If both the man and the woman are carriers, then their child will stand a 25% chance of developing the disease. With PGD, the embryos unaffected can be chosen for transfer.
sex related conditionsWith PGD, the sex of the embryos can be determined, which makes the technique a means to avoid sex related hereditary diseases.
Haemophilia A is a disease in which the blood does not clot properly and tiny wounds can become life threatening injuries. This sickness is inherited by females, but affects only males. If a woman is a carrier and she has a son, there is a 50% chance that he will be affected by the disease.
Thanks to PGD, embryos can be selected by sex and in this case, only female embryos would be replaced in the uterus.
How safe is PGS/PGD?
There are two possibilities when two cells are removed from an embryo: either the embryo survives the procedure, or it dies. The first is the rule, the second the exception to the rule.
It does not appear that embryos which survive the technique are damaged or compromised in any way. Follow-up has shown that children born from PGS/PGD embryos are as healthy and normal as those born of IVF and ICSI. However, further follow-up studies need to be performed in order to obtain a greater picture. For this reason, all couples who become pregnant via ICSI-PGS/PGD treatment are requested that they take part in the follow-up program of children. See
postnatal research.
Additional tests
In an estimated 5% of tests, PGS/PGD gives an incorrect result. That doesn't sound much, but it makes an additional test desirable. Therefore we advise you to allow follow-up tests to be performed in the CMG via prenatal investigations and/or amniocentesis.
How much does it cost
The difference between screening and diagnosis
More information over saviour babies?