Preimplantation genetic testing offers prospective parents insights into the genetic makeup of their future children. This testing identifies specific genetic conditions in embryos before pregnancy is established, supporting decisions for a healthy outcome.
Understanding PGT-M
Preimplantation Genetic Testing for Monogenic/Single Gene Disorders, or PGT-M, is a specialized genetic test. The “M” signifies its focus on monogenic, or single-gene, disorders, which arise from a mutation in a single gene. PGT-M identifies embryos at risk of inheriting a specific genetic disorder. Conducted with in vitro fertilization (IVF), it helps prevent the transmission of inherited conditions to offspring.
The PGT-M Process
The PGT-M process begins with in vitro fertilization (IVF), where eggs are retrieved and fertilized in a laboratory. Resulting embryos are cultured for several days. Once embryos reach the blastocyst stage (typically day 5 or 6), a small biopsy is performed. This involves carefully removing 5 to 10 cells from the trophectoderm, the outer layer that forms the placenta.
This allows genetic analysis without disturbing the inner cell mass, which develops into the fetus. Biopsied cells are sent to a specialized laboratory for DNA analysis, specifically for the genetic mutation of concern. Based on results, embryos unaffected by the targeted condition can be selected for uterine transfer.
Conditions Addressed by PGT-M
PGT-M detects specific single-gene disorders where the genetic mutation is known. This testing can be customized for nearly any single-gene condition, provided the familial mutation has been identified.
Examples of conditions commonly addressed by PGT-M include:
- Cystic Fibrosis
- Sickle Cell Anemia
- Huntington’s Disease
- Tay-Sachs Disease
- Spinal Muscular Atrophy
- Fragile X Syndrome
- Duchenne Muscular Dystrophy
- Thalassemia
- Hereditary cancer syndromes (e.g., BRCA1 and BRCA2 mutations)
PGT-M in Context
Preimplantation Genetic Testing encompasses several types, each focusing on different genetic aspects of an embryo. PGT-M specifically targets monogenic, or single-gene, disorders, distinguishing it from other forms of PGT.
PGT-A
PGT-A, or Preimplantation Genetic Testing for Aneuploidy, screens embryos for chromosomal abnormalities, meaning an incorrect number of chromosomes. These can include conditions like Down Syndrome, which results from an extra copy of chromosome 21. PGT-A is often used to identify embryos with the correct chromosome count, which can affect implantation and pregnancy success.
PGT-SR
Another type, PGT-SR, or Preimplantation Genetic Testing for Structural Rearrangements, is used when parents carry a chromosomal structural rearrangement, such as a translocation or inversion. These rearrangements can lead to an imbalance of genetic material in the embryo. Each PGT type addresses distinct genetic issues and is applied based on specific clinical indications.
Important Considerations
PGT-M is a highly accurate testing method, typically demonstrating an accuracy rate exceeding 95% and often reported as over 99%. However, it is important to understand that no test is completely without limitations. Occasionally, an embryo biopsy may not yield sufficient cells for analysis, leading to an inconclusive result. There is also a small chance of a false positive or false negative result, although these instances are infrequent.
For this reason, confirmatory prenatal testing, such as amniocentesis or chorionic villus sampling, is often recommended during pregnancy to verify the PGT-M findings. PGT-M screens only for the specific genetic disorder it was designed to detect and does not test for all possible genetic conditions, general birth defects, or future health concerns.