Preimplanting Genetic Diagnosis
Techniques of Preimplanting Genetic Diagnosis (PGD) allow studying the genetic characteristics of the embryo before its implantation in the uterus takes place. They are thought for those couples that have high risk of transmitting a certain genetic disease to their descendants, whether they are autosomic diseases, linked to sex, or chromosomic alterations.
PGD-FISH technique involves the following steps:
Embryo Biopsy: consists of the retrieval of one or two cells from every embryo to be analysed. A very precise micromanipulator is used, which allows performing the biopsy without harming the embryo.
Fixation of retrieved cells: In order to be able to carry out the test, it is necessary to “fix” the cell nucleus to perform the technique of fluorescence in situ (FISH) later and analyse the chosen chromosomes to be evaluated.
FISH: nucleus incubations with coloured “markers” are carried out. They will allow us to detect the analysed chromosomes later, by using a fluorescence microscope.
Reading of the chromosomes fluorescent “markers”: presence or absence of selected chromosomes is evaluated.
During the diagnosis process, the embryos are kept in In Vitro culture until the result is available, moment when the healthy embryos will be transferred to the uterus.
With Fluorescence In Situ Hybridization technique (FISH) we can also diagnose some numerical alterations. The improvement of these techniques, as well as the appearance of new markers and better knowledge of the genetic map will allow, in the near future, a wider use of Preimplanting Genetic Diagnosis.
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Retrieving of 1 cell from the embryo to be studied |
Analysis of evaluated chromosomes |
What cases is it indicated for?
Couples with high risk of transmitting a hereditary disease
Couples with risk of transmitting a chromosomic anomaly
Patients with recurrent miscarriages
Women at advanced reproductive age
Very severe male factors
Unexplained recurrent implantation failure
What new advantages does PGD offer?
It improves pregnancy rate
It reduces spontaneous miscarriage rate
It reduces the number of embryos to be transferred and therefore the risk of multiple pregnancy
Are all the embryo chromosomes analysed?
No. Depending on the chromosomes involved in the anomaly, only some chromosomes are analysed.
There are about 200 sex linked diseases, in other words linked to chromosome X, which are transmitted by women and only affect men. The most known are hemophilia and Duchenne’s muscular dystrophia, among others. Through the Preimplanting Genetic Diagnosis technique (PGD) it is possible, in these cases, to avoid the birth of children affected by transferring only female embryos.
Chances of achieving pregnancy with PGD diagnosis
Pregnancy rate per transfer is approximately 35-40%.
Is amniocentesis indicated?
It is always recommendable to carry out a prenatal diagnosis since not ALL the chromosomes are analysed; only some of them are.
What is the screening for aneuploidy?
It is the diagnosis of those chromosomes which are mainly involved in viable chromosomopathy. Chromosomes 13, 16, 18, 21, 22 and both sexual chromosomes X and Y are usually studied.
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Seremas | Medicine for men and women
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