Genetic Testing 101

What must you know about preimplantation genetic testing when going through IVF and should you consider it? We talk with Rachael Cabey, a Licensed Certified Genetic Counselor and a lead laboratory genetic counselor for Cooper Genomics and Jenna Miller, a Licensed Certified Genetic Counselor and a clinical science liaison for Cooper Genomics. Jenna travels around the US educating clinicians about genomics and genomic testing.

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Understanding the terms.
- Pre-2019
  - Preimplantation Genetic Testing (PGT)
  - Preimplantation Genetic Screening (PGS)
  - Preimplantation Genetic Diagnosis (PGD).
  - Current Terminology
    - PGS is now Preimplantation Genetic Testing for Aneuploidies (PGT-A).
    - PGD is now Preimplantation Genetic Testing for Monogenic/Single-Gene Disorders (PGT-M)
    - Preimplantation Genetic Testing for Chromosomal Structural Rearrangements (PGT-SR)
PGT-A
- What is PGT-A?
- Aneuploidy can cause what adverse outcomes?
- How many chromosomes can be screened for?
- Who should consider having this testing?
- What can PGT-A show us?
  1. Whole Chromosomal that are extra or missing.
  2. Difficult to detect a balanced translocation.
  3. What is a Polyploidy?
  4. Segmental aneuploidy? Smaller deletions or duplications
Because the missing or extra piece of chromosome is less severe than a whole extra or missing chromosome, segmental aneuploidies have a higher chance or resulting in a child born with physical or intellectual disabilities.
What do we mean by the resolution of the testing?
Is it possible to determine from which parent (the egg or sperm) the chromosome abnormality originated? Why might this be important?
What are the different testing platforms that can be used with PGT-A?
- Next Generation Sequencing (NGS)
- Single NucleotidePolymorphisms (SNPs)
Mosaicism
- What is mosaicism? (the presence of a mixture of chromosomally normal and abnormal cells)
- Not related to maternal age. Occurs after fertilization.
- Are there different degrees of mosaicism?
- Does the presence of mosaicism impact the implantation rate, miscarriage rate, and birth defect rate?
What does the research show on how PGT-A impacts the success rate of IVF?
- How is the test performed?
- How accurate is PGT-A testing? What is the risk of false negatives and false positives?
Preimplantation Genetic Testing for Monogenic/Single-Gene Disorders (PGT-M)
- What is PGT-M? (looks for specific inherited conditions controlled by a single gene)
- Alternative options
- Who should consider having this testing?
- Does PGT-M impact the success rate of IVF?
- Does this testing process differ from PGT-A?
- How accurate is PGT-M testing?
Preimplantation Genetic Testing for Chromosomal Structural Rearrangements (PGT-SR)
- What is PGT-SR?
- Who should consider having this testing?
- Does this testing process differ from PGT-A or PGT-M?
- How accurate is PGT-SR testing? Same range mid to high 90%
Important Additional Information
Patients and health care providers should be aware that a “normal” or negative preimplantation genetic test result is not a guarantee of a newborn without genetic abnormalities.
Importance of genetic counseling.