The Preimplantation Genetic Diagnosis (PGD) is a system of analyses that allow detecting chromosomal alterations and/or gene mutations in the embryos before they are implanted in the mother’s uterus. To carry out a PGD, it is necessary to undergo an in vitro fertilization, since this treatment will allow us to obtain embryos in the laboratory and thus have access to your genetic material.

This methodology is especially useful in cases of families who are carriers of  hereditary genetic diseases, caused by the presence of a mutation in the DNA of a gene.

There are three main types of monogenic diseases: dominant, recessive and linked with the X chromosome.

In the first case, the presence of a single mutation in a gene (inherited from the parent who carries it) is enough to cause the disease, while in the second case there has to be a combination of two mutations of the same gene, a carrier on the mother’s side and another on the father’s, to develop the disease. As to X-linked diseases, they can be dominant or recessive, but they are particular in that they are transmited in accordance with the inheritance of sex chromosomes.

Each person has two copies of their genetic material, but only one is transmited to their children; that is, one embryo is made up of one copy of the father’s genetic material and one copy of the mother’s. Therefore, for one specific gene, it is possible to inherit the healthy copy or the mutated copy of each parent.

This diagnostic system also allows selecting healthy embryos in the case of couples in which one of the members is the carrier of a chromosomal translocation, that is, that in their chromosome set there has occurred a chromosome reorganization or fusion. These reorganizations do not cause phenotypic effects in the carrier, but chromosomally unbalanced gametes can be generated.

With PGD we can see which embryos are blanced and which are not and, therefore, choose the ones without any chromosomal alterations.

Finally, PGD also includes what we call “Aneuploidy Screening”.

Preimplantation “screening” consists in conducting a study of all the chromosomes of the embryo and determining whether there is any alteration. With this system we can select the embryo that shows no alteration to transfer it to the mother’s uterus and then attain the correct development of pregnancy and birth of a healthy baby.

This technique can benefit couples that have suffered miscarriages in a recurrent manner, couples that have undergone several IVF cycles unsuccessfully and couples in which the woman is of advanced age or the the man has an alteration of meiosis.

The commun denominators in these cases are aneuploidies or chromosomal alteraciones. Most of these alterations are not present in the cells of the entire body of the parents, rather they originate only in the gametes or the embryos that are derived.

These alterations can consist in the gain or loss of fragments of or entire chromosomes and they can produce viable syndromes such as the Down Syndrome (an extra chromosome 21), Edwards Syndrome (an extra chromosome 18) or the Patau  Syndrome (an extra chromosome 13) in newly-born children, but they can also cause the embryo not to be viable and to fail to become implanted in the mother’s uterus, or to not evolve well after implantation resulting in a miscarriage.

 Dominant Autosomal Diseases

• Huntington
• Renal polycystic disease, AD. Linked to PKD1
• Neurofibromatosis type 1
• Charcot-Marie-Tooth 1A
• Ataxia Espinocerebelar, SCA1, SCA3
• Tuberous sclerosis type 1
• Hereditary multiple exostosis
• Endocrine Multiple Neoplasia 2A
• Hereditary, non-polypsic colon cancer (S. Lynch)
• Familial polypossatomatosis
• Tuberous sclerosis type 2
• Von HippelLindau Syndrome
• Family spastic paraparesis
• Renal polycystic disease, AD. Linked to PKD2
• Pigmentary Retinosis