PGT-SR (preimplantation genetic testing for structural rearrangements) is a test developed for carriers of chromosome rearrangements
Chromosome rearrangements are formed when one or more pieces of chromosomes, the structures that contain an individual’s genetic material, find themselves in an altered position. For example, one common type of rearrangement, called a ‘translocation’, occurs when there is an exchange of materials between two chromosomes.
Approximately 1 in 500 people carry a chromosome rearrangement. People who have a balanced chromosome rearrangement in their cells are usually healthy, but they are at increased risk of producing pregnancies where the fetus has pieces of chromosome lost or duplicated. This loss or duplication of parts of a chromosome often leads to miscarriage, or the birth of children with disabilities.
Insertion is when a fragment of a chromosome is detached from its original place and inserted into another chromosome.
When two breaks occur on the same chromosome, and the resulting fragment rotates before inserting back into the chromosome, this leads to ‘inversions’. When eggs or sperm are produced, the normal and inverted copies of the chromosome come together and exchange pieces. The presence of the inversion can result in a proportion of the gametes to lose parts of the affected chromosome, while duplicating other areas.
Juno Genetics’ PGT-SR technology uses next-generation sequencing in order to provide the best possible accuracy rates (exceeding 95%). The highly-validated test assesses thousands of sites on each chromosome, measuring the amount of DNA at each point in order to calculate the number of chromosomes. In many cases, this analysis is supplemented by analyzing variations in the DNA sequence, known as single nucleotide polymorphisms (SNPs), further enhancing the accuracy of the test.
A detailed description of the PGT[SR]Seq method and its requirements is given in the Juno Genetics User Manual. In brief, Juno can undertake a new PGT[SR]Seq case once a genetic report describing the chromosomal rearrangement has been received and a Juno scientist has confirmed that PGT[SR]Seq is technically possible. A completed Requisition Form, formally requesting PGT[SR]Seq and providing relevant information concerning the patients, is also required. Rarely, PGT[SR]Seq is not technically possible. For this reason, patients should not begin a cycle until Juno has reviewed the patient’s genetic report and confirmed that PGT[SR]Seq is feasible.