Preimplantation Genetic Test (PGT)
The Preimplantation Genetic Test (PGT) is a preimplantation genetic diagnosis procedure that allows for the assessment of the embryonic health status in all couples undergoing in vitro fertilization, even if they are not carriers of genetic diseases.
It also allows for the identification of the presence of monogenic diseases or chromosomal alterations in embryos generated in vitro by couples at high reproductive risk, before their implantation in utero.
Prenatal diagnosis involves the use of techniques such as chorionic villus sampling or amniocentesis, and allows for the identification of genetic abnormalities within the first 10-16 weeks of pregnancy in couples at risk of transmitting a genetic disease to their offspring.
The two procedures involve sampling fetal cells from which DNA will be extracted to analyze mutations of specific genes and/or determine the fetal karyotype.
Having the option of an alternative to prenatal diagnosis is of great utility for couples at genetic risk, preventing them from resorting to therapeutic abortion.
Prenatal diagnosis is not accepted in various populations due to ethical/moral or religious issues associated with pregnancy termination.
The evolution of in vitro fertilization (IVF) techniques, and the ability to obtain gametic and embryonic cells usable for the diagnosis of genetic diseases, has allowed the shift of the diagnosis period from the "post-implantation" phase to the "pre-implantation" phase.
This preimplantation genetic diagnosis procedure requires an in vitro fertilization cycle to be performed.
Subsequently, the generated embryos will undergo biopsy and subsequent genetic analysis.
At the C.M.R, as in the most specialized centers, the material on which the genetic examination is performed consists of multiple cells taken on the fifth/sixth day of in vitro culture (trophoderm) at the blastocyst stage.
This stage of embryonic development ensures greater accuracy of the genetic analysis, as well as greater resilience of the embryo to the stress experienced during the procedure. The collected material will then be sent to the GENOMA molecular genetics laboratory in Rome for analysis. The embryos that are found to be normal in the genetic analysis, previously cryopreserved at the end of the biopsy, can then be transferred into the uterus.
The C.M.R has been performing PGT since 2013.
During fertilization, processes of genetic material recombination occur, which in some cases can generate chromosomal alterations.
Chromosomal alterations can be numerical (when there are more or fewer chromosomes than normal) and structural (when a portion of a specific chromosome is missing, located on another chromosome, or inverted).
Sometimes the alteration can occur in a specific gene (monogenic), leading to a particular pathology that can be transmitted to offspring in various ways.
There are various forms of application for Preimplantation Genetic Testing:
In this case, the selection of embryos to be transferred into the uterus is based not only on their morphological appearance but also on their chromosomal (numerical) makeup, allowing for the transfer of embryos that are chromosomally normal according to genetic analysis and have a high potential for reaching birth.
Examples of pathologies caused by chromosomal aneuploidies identifiable with PGT-A include Down syndrome, which occurs when there are three chromosome 21s (trisomy 21) instead of two, trisomy 18, trisomy 13, 45X (Turner syndrome), 47XXY (Klinefelter syndrome), 47XYY, and 47XXX.
This test allows for the detection, in embryos generated in vitro by couples at high reproductive risk, of the alteration or mutation of a specific gene that would cause a monogenic or Mendelian disease in the offspring.
Currently, there are diagnostic protocols for over 200 monogenic diseases, including autosomal dominant, recessive, or X-linked conditions.
Common genetic disorders in Italy where PGT-M is effectively applied include: Beta-Thalassemia, Sickle Cell Anemia, Hemophilia A and B, Duchenne-Becker Muscular Dystrophy, Myotonic Dystrophy, Marfan Syndrome, Cystic Fibrosis, Spinal Muscular Atrophy (SMA), Huntington's Disease, and Fragile X Syndrome.
This test allows for the detection of structural chromosomal anomalies caused by the incorrect breakage or joining of chromosomal segments, leading to the final result of a disease.
There are many types of structural alterations: translocations, deletions, duplications, insertions, ring chromosomes, or inversions.
These alterations can be balanced or unbalanced.
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