Preimplantation Genetic Testing for Structural Chromosomal Rearrangements


What is PGT-SR?

PGT-SR, preimplantation genetic testing for structural chromosomal rearrangements, is a genetic test performed on embryos created through IVF to screen for chromosomal structural rearrangements normally caused by balanced translocations and inversions.


Chromosomal rearrangements can be inherited or may occur spontaneously (de novo). It is estimated that 1 in every 500 people carry a balanced reciprocal translocation. Most are unaware of their balanced translocation carrier status and live normal healthy lives. A person typically becomes aware of their carrier status once they try to have children.

Carriers of balanced rearrangements can pass down the same rearrangement or may produce embryos with unbalanced chromosome rearrangements. This usually does not lead to a successful pregnancy or may result in the birth of a child with genetic abnormalities. PGT-SR can increase your chances of a successful pregnancy by examining embryos with chromosomal rearrangements, ensuring only those with the correct amount of chromosomal material are selected for transfer.

What is a chromosomal structural rearrangement?

Chromosomes are the structures that house the genetic material that directs our growth and development. When a structural rearrangement occurs, the chromosomes are altered in such a way that their normal rearrangement or size changes. Your chromosomes can undergo rearrangements that include the following:

  • Duplications: A segment of the chromosome is repeated
  • Deletions: A segment of the chromosome is missing
  • Inversion: A segment of chromosome reverses its orientation
  • Translocation: A segment of the chromosome changes its location. Two different types of translocations are observed.


Inversions occur when a segment of chromosome is flipped and reinserted upside down inside the chromosome. The two types of inversions observed are paricentric and paracentric inversions. Paricentric inversions involve the centromere while paracentric inversions do not. Embryos created by a person with an inversion may have missing or duplicated chromosome material.


Reciprocal Translocations

A reciprocal translocation occurs when two different segments of genetic material break off from their chromosomes and swap places. When this occurs and there is no net gain or loss of genetic material, the translocation is balanced. If this same exchange occurs and there is a net gain or loss in genetic material, the translocation is unbalanced. People that are carriers of a balanced translocation can have children with either the same balanced translocation, an unbalanced translocation, or a normal set of chromosomes.


Robertsonian Translocations

A Robertsonian translocation occurs when two different chromosomes join together to form one large chromosome. This results in an abnormal chromosome count of 45 instead of the normal 46. The most commonly seen Robertsonian translocations are between chromosomes 13/14 and 14/21.

Who is PGT-SR for?

If you are a carrier of a translocation or inversion, PGT-SR is recommended for you.

The PGT-SR Process

Once your physician or genetic counselor determines PGT-SR is appropriate, PacGenomics will conduct a review of your translocation or inversion. Your embryo biopsy samples are then sent to our lab where testing is conducted. PGT-SR screens out embryos that carry unbalanced translocations, ensuring only those with the correct amount of genetic material are selected for transfer.

PGT-SR with PacGenomics

PacGenomics PGT-SR platform has been developed to take on even the most difficult cases. With our high resolution NGS based technology, we are able to detect even the smallest breakpoints. PacGenomics often receives referrals from other PGT labs who are unable to take on these complex cases, striving to ensure every patient has access to testing.