PGT-SR
Specialized testing for chromosomal structural rearrangements.
What is PGT-SR?
PGT-SR, or preimplantation genetic testing for structural rearrangements, is a specialized type of genetic testing used in the field of reproductive medicine. It's designed for individuals or couples who are known carriers of chromosomal structural rearrangements, such as translocations or inversions. These structural changes in chromosomes can lead to fertility issues, recurrent miscarriages, or the birth of a child with a genetic disorder. In PGT-SR, embryos created through in vitro fertilization (IVF) are tested for these specific chromosomal rearrangements before being transferred to the uterus.
What is a Translocation?
A translocation is a type of abnormality in the structure of a chromosome. There are two main types of translocations: reciprocal (also known as non-Robertsonian) and Robertsonian. Reciprocal translocation is the more common type. In a reciprocal translocation, a small portion of two separate chromosomes have “swapped” positions with each other.
Detecting Translocations with PGT-SR
Couples in which one partner has a translocation usually have a history of recurrent miscarriage. During the evaluation, a chromosome analysis on both partners identifies the translocation abnormality.
At this point, their options are to continue to try to conceive naturally, use a donor (egg or sperm depending on which partner is the carrier), or use PGT-SR. If they decide to try PGT-SR, blood is obtained from the affected partner so that the translocation can be characterized.
Specific fluorescent probes are used that recognize and attach to an entire chromosome. For example, a translocation between chromosomes #4 and #11 would require whole chromosome probes for each of those chromosomes. Each probe would have a different color for easy identification. After an embryo is obtained from IVF, the polar body or blastomere (or sometimes both) are removed from the embryo. These biopsied cells must be at a certain stage in order for the process to work, so they are converted in the lab. The probe is then applied and read. A normal chromosome would appear with a single color. A chromosome with a translocation will show two colors.
In this way, embryos can be identified that do not have translocations and can then be transferred to the uterus.
