Our Tests

PGD for Translocations and Chromosomal Rearrangements

What are translocations/chromosome rearrangements?

Chromosomes are the structures in our cells that carry our genetic information (genes). Typically, we have 46 chromosomes in each of our cells that are arranged in 23 pairs. Different types of chromosomal rearrangements include:

  • Translocations: in which segments of two chromosomes break off and change places
  • Inversions: in which a segment of a chromosome has reversed orientation
  • Deletions: in which a segment of a chromosome is missing
  • Duplication: in which there is an extra segment of a chromosome
  • Insertion: where a segment of a chromosome has been inserted into the incorrect location
diagrams

Individuals who carry a balanced translocation or inversion have all the correct genetic information; however sections of genetic material are found in a different position than expected. These individuals are typically healthy; however, they are at increased risk for infertility, miscarriage, stillbirth, and/or having a child with a chromosome abnormality as a results of an unbalanced form of their rearrangement.

What is PGD for translocations/chromosome rearrangements?

Preimplantation genetic diagnosis (PGD) for translocation/chromosome rearrangements is a method used to identify embryos that have the correct amount of genetic material (balanced/normal) and embryos that have extra or missing genetic material as a result of the translocation or rearrangement (unbalanced). PGD can reduce the likelihood of a failed implantation or an early miscarriage, or of having a child with a chromosome abnormality (which can lead to birth defects and intellectual disabilities), and increases the chances of a healthy pregnancy after an IVF cycle.

How does RGI test for chromosomal rearrangements?

PGD is performed on embryo biopsy samples. Following an egg retrieval and fertilization, one or more cells are removed from a blastomere (day 3 embryo) or blastocyst (day 5/6 embryo). These biopsied cells are shipped to our lab for PGD analysis.

PGD for translocations typically does not require the submission of any parental blood samples or work-up prior to testing. This is determined on a case-by-case basis, upon review of the translocation report.

PGD can be performed by three possible methods:

  • Next-Generation Sequencing (NGS)

    Next-Generation Sequencing (NGS) is a state-of-the-art technology which analyzes the number of all 24 chromosomes (pairs 1-22, X and Y). NGS is a method in which the DNA sequence of the embryo biopsies is directly analyzed. This can detect chromosomal imbalances related to a previously identified translocation. In addition to testing for the translocation, this technology also provides information about other spontaneous chromosomal abnormalities that are associated with failed implantation, miscarriage, or live births with multiple anomalies.

    The optimal accuracy for this testing is 95%, when performed on a blastocyst (day 5/6) embryo biopsy.

  • Array Comparative Genomic Hybridization (aCGH)

    Array Comparative Genomic Hybridization (aCGH) is a technology which analyzes the number of all 24 chromosomes (pairs 1-22, X and Y). aCGH is a method in which the DNA of the embryo biopsies is compared to a normal control sample. This can detect chromosomal imbalances related to a previously identified translocation. In addition to testing for the translocation, this technology also provides information about other spontaneous chromosomal abnormalities that are associated with failed implantation, miscarriage, or live births with multiple anomalies.

    The optimal accuracy for this testing is 95%, when performed on a blastocyst (day 5/6) embryo biopsy.

  • Fluorescence in situ Hybridization (FISH)

    With recent advances in next generation technologies (NGS), FISH-based testing for chromosomal rearrangements (PGT-SR) will be replaced with NGS. This is applicable for rearranged translocated fragments for larger than 4 - 5 Mbp.

    Prior to the patient initiating ovulation stimulation, the translocation case should be re-reviewed by RGI to determine feasibility.