It is possible to genetically profile patients’ embryos who have several hereditary familial disorders. Patients having a history of gender-related illnesses as well as those with single gene disorders (such as cystic fibrosis or sickle cell anemia) are specifically included in this. Furthermore, even families looking for a bone marrow donor can use PGT to conceive a kid whose stem cells will match those of an affected sibling.
What is preimplantation genetic testing?
To reduce the risk of passing down inherited diseases, preimplantation genetic testing (PGT) is a laboratory procedure used in conjunction with IVF treatment in Turkey. Specific single-gene disorders (such as cystic fibrosis or sickle cell anemia) and structural chromosomal alterations in a parent are some of the most frequent causes of PGT. PGT can be used by families to have a child who will be able to supply compatible stem cells in the event that a member of the family requires a bone marrow donor. (1)
What are the different types of preimplantation genetic testing?
Preimplantation genetic testing for monogenic disorders (PGT-M) , as described above, searches for the mutation responsible for the disease and selects the embryos free of this mutation. Preimplantation genetic testing for aneuploidy (PGT-A) is a broader test that monitors for aneuploidy on all chromosomes which include 22 pairs of autosomes and the sex chromosomes X and Y. Pre-implantation genetic testing for structural rearrangements (PGT-SR) is used to assess the risk for chromosome gains and losses linked to parental structural chromosomal abnormalities (such as translocations, inversions, deletions, and insertions). (2)
Who is a candidate forPGT-M?
The majority of couples who require these procedures are not infertile; rather, they have a history of the disease in their family and want to lessen the possibility of having another child who will have serious health issues or die before their due date. However, PGT may be an option for couples who are seeking reproductive therapy and are occasionally discovered through widely accessible genetic screening to be at risk of passing on an inherited condition.
Almost all genetic diseases for which the precise mutation is known can be treated with PGT. But every pair needs a different test, which must be developed. Before the IVF cycle begins, this test design may take several months to complete. (3)
The technique used is polymerase chain reaction (PCR), an amplification procedure creating numerous copies of the target gene. The identification of extremely minute amounts of DNA for diagnosis is made possible by this amplification technique.
When is PGT-A used?
PGT-A by Next Generation Sequencing (NGS) quantifies the number of chromosomes in each embryo biopsy to differentiate between chromosomally normal (euploid) embryos with 46 chromosomes which can implant and generate a pregnancy and chromosomally abnormal (aneuploid) embryos which cannot implant or will ultimately end with a miscarriage.
PGT-A is classically proposed for patients with advanced maternal age or for younger women to decrease the time to pregnancy.
How does PGT work?
Multiple eggs are developed and harvested during IVF for PGT. Oocytes, or primitive egg cells, are fertilized by intracytoplasmic sperm injection using a single sperm.
The resultant embryos are maintained up to the third or fifth day of embryo development.. At this moment, one or two embryonic cells or five to six blastocyst cells are taken out for a biopsy. The embryo’s surviving cells are not harmed by this process.
The presence of particular genetic conditions is assessed in isolated cells. On the fifth day of embryo growth, embryos that are found to be unaffected are returned to the woman’s uterus if the biopsy was taken on day 3 and frozen thawed if the biopsy was taken on day 5.
Finally, the right thing to do is to consult a fertility clinic with embryology laboratory staff, and extensive experience in embryo micromanipulation and biopsy. Your genetic counselor will coordinate your cycle with the IVF team and PGT lab to make the process as smooth as possible.
What percentage of IVF embryos are genetically abnormal?
PGT-A test cannot fix genetic issues in embryos, but it can detect any underlying genetic abnormalities that make them unsuitable for transfer, even if they have developed to the blastocyst stage and look normal. Research has shown that depending on the woman’s age when the eggs were retrieved, roughly half of human embryos that have developed to the blastocyst stage and appear normal are genetically abnormal. As a result, transferring an embryo that has undergone PGT-A testing reduces the likelihood of miscarriage and improves pregnancy success rates per embryo transferred.
In the laboratory setting, certain genetically abnormal embryos may develop into the blastocyst stage. It has been observed that around 40-50% of blastocysts in humans are genetically normal, but this percentage decreases to 10-15% when the eggs are collected from a woman aged 42.
PGT-A is particularly beneficial for couples who have a genetic predisposition to abnormality due to a rearrangement of their chromosomes, called translocation. This rearrangement affects around 1% of the population, resulting in an increased risk of aneuploidy in their embryos. Individuals with balanced translocations often experience repeated miscarriages and can greatly benefit from PGT-A.
Baruch, S., Kaufman, D., & Hudson, K. L. (2008). Genetic testing of embryos: practices and perspectives of US in vitro fertilization clinics. Fertility and sterility, 89(5), 1053-1058.