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Pre-Implantation Genetic Diagnosis (PGD)

What is PGD?

 

Pre-implantation genetic diagnosis is a diagnostic technique that allows us to identify abnormalities in an embryo’s genes or chromosomes before it is transferred to the uterus. This means that children are born healthy and we can eradicate family genetic pathologies.

 

 

What is the process?

 

• The first step is to visit an assisted reproduction centre, where specialists, geneticists, embryologists and gynaecologists can carry out a comprehensive study of the family history and analyse all the tests, so that they can give the most appropriate advice to each patient, and propose the best treatment in each case. All communication with patients during genetic consultation prior to PGD must be clear, concise, and fully comprehensible. We will offer this treatment wherever genetic diagnosis is technically possible, where there is a high and reliable chance of success, and where this method of assisted reproduction is practical.
• Once a patient has decided on treatment, and if a pre-implantation genetic diagnosis is recommended, we go ahead with IVF treatment. When the embryo reaches a development of 6 to 8 cells, on the third day of culture, we carry out a biopsy, which consists of making a small incision in the pellucid area of the embryo (if we compare the embryo with an egg, the pellucid area is like the shell), and a cell is extracted, called the blastomere. The nucleus of this cell holds all the genetic information of the embryo, which we can then analyse to discover what is happening to the embryo. This process in no way damages the condition of the embryo, which is not affected and continues its development as normal.

 

 

If it is necessary to carry out a chromosome study of aneuploidy (number) translocation and inversion (structural abnormalities), we use the fluorescent in situ hybridisation (FISH) method. If we need to analyse a monogenic illness we use the molecular biology technique, polymerase chain reaction (PCR).

 

1st round: MultiVysion PB Panel	2nd round: MultiVysion 4CC Panel

 

 

• 24 to 48 hours after the embryo biopsy, we can transplant the healthy embryo into the uterus, and the embryonic treatment is complete. Once this is done it is just a matter of waiting for the embryo to implant itself in the uterus. Leading to pregnancy and a baby that will neither suffer from the inherited illness nor pass it on to future offspring. The illness is thus eradicated from the family genes.

 

Which patients use PGD?

 

Patients who may benefit from PGD are those who have experienced the following:

 

• Repeated failure of implantation

  Patients who have not become pregnant after several embryonic transplantations with healthy embryos. In these cases we carry out a genetic analysis to determine if a significant number of embryos have an abnormal number of chromosomes. This may be causing the problem.

• Women older than 38 to 40

  The risk of chromosome abnormality increases with age, as older eggs are more likely to reproduce chromosomes incorrectly in cells. This can result in embryos with abnormal chromosomes, which in turn can lead to repeated failure with implantation, problems with the foetus, or miscarriage.

• History of spontaneous miscarriage

  In patients who present no other explanation of the problem, it has been found that chromosome abnormalities account for 50% of miscarriages.

• Men with a very low sperm count

  It has been found that there is a significant increase in chromosome abnormalities in sperm in a high percentage of men with a low sperm count, which can lead to embryos with chromosome defects. Patients with indications of abnormal sperm are advised to undergo a chromosome study before treatment using the FISH technique, and if this shows a high number of cells with an abnormal chromosome count we would recommend PGD.

• Translocation, inversion and other chromosome abnormalities

  Problems relating to chromosome structure or balance will have no clinical manifestation, but can result in gametes, eggs or sperm with an unbalanced number of chromosomes, which may produce abnormal embryos and unsuccessful implantation, miscarriage, or children born with genetic illnesses.

• Monogenetic illnesses

  Monogenetic illnesses are due to genome mutations, which depending on whether they are inherited in the dominant or recessive form, can affect foetuses in different ways. To detect these illnesses in embryos we use highly complex techniques in molecular biology. It is currently possible to diagnose many monogenetic illnesses in the embryo, including cystic fibrosis, Duchenne and Beckett muscular dystrophy, fragile X syndrome, thalassemia, falciform anemia and Marfan syndrome.

 

 

Did you know ...

 

... Karyotype is the metaphysical arrangement of chromosomes in a cell according to its size and morphology . a human cell has 46 chromosomes, in 23 pairs, arranged in 22 autosomal pairs and one sexual pair (men 46XY and women 46XX).

 

... The 2 metres of DNA in a human cell is formed in a double helix of complementary nucleotides, that use proteins to arrange themselves in different structures to form the 46 chromosomes.