PGT-SR: structural chromosome defects

Pre-implantation genetic testing of structural chromosomal defects (PGT-SR), previously pre-implantation genetic diagnosis (PGD), is suitable for couples in which one or both partners carry a balanced translocation or other structural chromosome rearrangement. At present, most translocations can be investigated using the Next Generation Sequencing (NGS) method.

What are translocations?

Translocations are the most common structural abnormalities of chromosomes, which occur at a frequency of about 1:625. There are no signs of developmental defects or other disabilities or diseases in subjects who are carriers of a balanced translocation. The problem lies in reproduction where sperm or eggs may be produced which do not contain the right amount of genetic material, i.e. a certain part is missing or doubled. If such sperm and eggs are involved in fertilization, a genetically abnormal individual with multiple developmental defects and severe organ disabilities will develop. In the vast majority of cases, the situation will lead to miscarriage or the developmental defect is detected in prenatal diagnosis.

How is PGT of translocations performed?

At present, embryonic translocation testing may also be performed using microchip technology, using special chips with higher resolution, which can detect even very minor defects at the level of chromosome parts. The advantage of using NGS is that the detection of translocations may be performed together with pre-implantation testing of aneuploidies.