The Pre-implantational genetic diagnosis (PGD) is a technique which permits to identify genetic and chromosomal anomalies in the obtained embryos by means of an In Vitro Fertilisation treatment through ICSI, before these are transferred to the maternal uterus. The procedure consists of obtaining genetic material of each embryo, analyse it and determine the healthy embryos that can be transferred.
Why is it done?
There is a wide host of genetic alterations which increase the risk of suffering a disease; others although not being compatible with a disease can hinder pregnancy.
This wide variety of genetic alterations can be classified taking into account if they affect large chromosomal regions or just the function of one gene:
- Numeric anomalies (aneuploidies) are those which affect the number of repetition of the whole chromosome or just part of it. Down syndrome which presents an extra chromosome in the normal pair 21 is one of the most common.
- The structural anomalies implicate a change in the normal order in the sequence throughout one or various chromosomes. Within this group situations could arise when some chromosome regions are interchanged between different chromosomes.
- Monogenic diseases and rare illnesses of genetic origin are those conditions which molecular pathology alters the normal function of one or various genes. The origin of these alterations can be associated to mutation and variations in the number of times they should appear or should be present in tiny regions of the genome related to the genes which are affected.
¿Cómo se realiza?
The complexity of these techniques consists in the design of the necessary tools for the analysis. It is a therapeutic work within what is known as personalized medicine. For the chromosomal analysis the same tools can be used for all individuals. For monogenic illnesses which cover smaller regions it is necessary to carry out a previous study to get information about the gene damage points in the affected progenitor and direct family members.
The genetic analysis of the embryos is carried out from cells extracted on day 3 or day 5 of embryonic development, in this way, we have time to make the analysis and select the healthy embryos that can be transferred to the uterus.