Preimplantation Genetic Diagnosis (PGD)

PGD aim is to enable the transfer of those embryos diagnosed as healthy

What does this consist of?

Preimplantation Genetic Diagnosis (PGD) is a technique that consists of a genetic analysis of embryos in their early stages of development in vitro, the aim of which is to enable the transfer of those embryos diagnosed as healthy.

PGD must be done as an adjunct to assisted reproductive technology. Couples must undergo a cycle of IVF, given that ovulation induction and the subsequent recovery of oocytes by way of vaginal puncture must produce a sufficient number of oocytes, and later embryos, that guarantee the transfer of at least one normal embryo for the genetic diagnosis study.

PGD was seen to be an alternative to a prenatal study, attempting to avoid interruptions to pregnancies in those cases where fetuses were affected, and was directed towards patients with severe hereditary diseases.

When is it recommended?

Patients with severe hereditary diseases

The law 14/2006 of May 26, regarding Techniques of Assisted Human Reproduction, permits authorized centers to perform this type of diagnosis in cases of severe hereditary diseases, of early appearance, and which are not receptive to curative treatment, according to current scientific knowledge; as well as to detect of other alterations that could compromise the viability of the embryo.

Other use

The application of PGD techniques for any other use or when its intent is for therapeutic ends require the express authorization, case by case, of the corresponding health authorities.

PGD types

  1. • Recessive diseases associated with the X chromosome: hemophilia, hemophilia, Duchenne muscular dystrophy, Fragile X Syndrome, etc.

    • Monogenic autosomal recessive diseases: cystic fibrosis, spinal muscular atrophy, severe combined immunodeficiency, sickle cell anemia, etc.

    • Monogenic autosomal dominant diseases: Huntington´s diseases, mytotonic dystrophy, Marfan’s syndrome, etc.

    Monogenic diseases are caused by a single alteration, change, or very small mutation produced in a gene. These changes in the genes are hereditary and can be recessive (for the disease to manifest itself, both the maternal and paternal genes must be affected) or dominant (it is sufficient that only one of the genes, maternal or paternal, be affected). On the other hand, these small changes can be produced in the sex chromosomes (diseases related to gender) or in the autosomal chromosomes (non-sexual chromosomes).

    Depending on whether the genes involved in the illness are dominant or recessive or if the genes are gender-based or autosomal, the couple will have a greater or lesser probability of passing it on.

    PGD for monogenic diseases makes it possible to distinguish between genetically normal and affected embryos. Thanks to this diagnosis, we can greatly reduce the risk of conceiving offspring with severe monogenic diseases.

  2. • Structural chromosomal abnormalities: this refers to an abnormality in the content of the chromosome, which is to say a piece has changed place or is lacking: such as is the case in translocations, inversions, and deletions. The most common example of chromosomal reorganization is translocation. When one member of a couple is the carrier of a translocation, they often have difficulties having offspring, either because they don´t reach gestation or because despite getting pregnant they suffer repeated miscarriages and do not reach the full term of pregnancy. This is due to the fact that the carrier of the said abnormality produces gametes (sperm or oocytes) that are unbalanced and which give rise to abnormal embryos that either don’t implant well or miscarry. One of the options for these couples is to undergo a PGD so as to choose chose embryos which are healthy and balanced, and then place them in the uterus so as to produce a healthy child.

    • Numerical abnormalities: these produce an abnormality that affects the number of chromosomes: Klinefelter’s Syndrome (XXY), Syndrome XYY.

    • An aneuploidy study or preimplantational screening: this attempts to study the highest number of chromosomes possible in accordance with the current and available techniques so as to improve the rate of gestation in IVF patients with a poor prognosis (advanced maternal age, failures of implantations, repeated miscarries, severe masculine factor…) Humans have 23 pairs of chromosomes. Each pair is made up of a paternal and maternal chromosome. Thanks to the latest advances in PGD technology, we can detect the presence or lack of a series of chromosomes or all chromosomes by using Array-Comparative Genomic Hybridization (CGH-ARRAY) from a single cell (a biopsied blastomere). The application of this technique allows us to study the aneuploidy of the embryos and reduce the risk of trisomic pregnancies (for example: Down´s Syndrome) and other numerical abnormalities that would impede implantation of the embryo or produce a miscarriage.

  3. Genetic selection of compatible embryos to cure siblings affected by diseases such as Fanconi anemia, thalassemia, Wiscott-Aldri Syndrome… thereby making available at the moment of birth cells from the umbilical cord so as to perform an hematopoietic stem cell transplantation (HSCT) in the affected sibling.