What is Preimplantation Genetic Diagnosis (PGD)?
A testing process for one or more genetic diseases with a risk of family recurrence in the embryo.
The preimplantation genetic diagnosis was used for the first time to select a female fetus by looking for the presence of a Y chromosome in a pair with an X-linked disease. (1991) Afterwards, it started to be used in many diseases such as sickle cell anemia, Tay-Sachs, Duchenne muscular dystrophy, and beta-thalassemia. Today, it can be used successfully for almost all diseases whose molecular diagnosis we know.
During these evaluations;
• Is there a risk of recurrence in new pregnancies of the family?
• Has the cause of the disease been determined?
• Is the mutation specified as determined as the real cause of the disease?
• Is the detected disease suitable for PGD?
• Are there any ethical problems with these tests?
With these evaluations, the appropriateness of the test is determined.
FOR CHROMOSOME DISEASES (PGT-A AND PGT-SR)
PGT-A is used to screen for whole chromosomal aneuploidies or losses and gains of large fragments.
PGT-SR is used to screen for smaller chromosomal losses and gains than PGT-A
Previously, the FISH method was used to investigate chromosomal abnormalities; Today, this method is almost abandoned in most centers because of its low reliability.
Today, next-generation sequencing (NGS)-based methods are used, showing us the numerical changes of all chromosomes in the embryo with very little DNA. Sometimes we need to do this test due to a balanced translocation in one of the partners.
To make this method more reliable, especially if the part of the chromosome displaced at the translocation is small, PGT-SR, in which we increase the resolution and can see smaller changes, and if necessary, other molecular methods are used together. With this method, 4-5 million base part replacements can be diagnosed.
ESHRE recommendations for PGT-A are as follows.
• Advanced female/maternal age
• Recurrent implantation failure
• Repetitive Low. It should be noted that those with a history of recurrent miscarriage have a natural chance of successfully conceiving and PGT-A is not recommended for recurrent miscarriage without a genetic cause.
*The ESHRE Guideline Group on RPL et al., 2018
Recommendation of our center: These patients should undergo genetic evaluation before the procedure and it should be evaluated whether they will benefit from this procedure.
• Severe male factor (SMF)
Please contact our center for the selection of the appropriate method.
FOR SINGLE GENE DISEASES (PGT-M)
The PGT-M method is used for families with or carrying a single-gene disease.
It is possible to test for one or more genetic diseases with a risk of recurrence in the embryo in the family.
The rate of consanguineous marriage is very high in our country. Although statistical studies give a figure of 26% for the frequency of consanguineous marriages, the rate is higher especially when we consider marriages from the same village. The rate of being a carrier for at least one disease in consanguineous couples is approximately 30%, and the rate of sick children per pregnancy is 7.5%.
In such cases, very good clinical information should be obtained from the family and screening should be planned for diseases that exist in the family first. If the family wishes, pre-pregnancy screening packages can be applied. (See Pregnarisk)
In addition, the diseases that both of them are carriers can be determined with large gene panels to be made to spouses in consanguineous marriages, and the selection of embryos that do not carry these diseases can be achieved by the PGT-M method.
For the selection of an appropriate method, please contact our center
Important note: PGT tests, nowhere in the world, can reduce the risk to zero. Follow-up should be continued during pregnancy and the possibility of making test plans according to the features of the disease should be discussed with the geneticist.