Genetics. PGD and PGS
Preimplantation Genetics Diagnostic (PGD) and Preimplantation Genetics Screening (PGS) help reduce the risk of genetics disease (e.g. Beta-Thalassemia and sickle cell anemia) and chromosomal abnormalities responsible for implantation failure, miscarriage or syndromes (such as Trisomy 21 or Down’s Syndrome). AAFC Genetic provides a wide range of genetic services to help couples achieve a healthy pregnancy and improve the success of IVF. PGD and PGS are offered seven days a week with rapid turnaround time allowing next day embryo transfer.
PREIMPLANTATION GENETIC DIAGNOSIS & IVF RELATED GENETIC TESTS
- Pre-PGD genetic investigations.
- Known mutation analysis for parents, affected child and relatives.
- HLA-typing - HLA- A+B+C or A+B+DR
- Carrier Screening for >2000 mutations causing > 250 disorders.
- Sperm DNA Fragmentation Testing.
- Y-Chromosome microdeletions Testing.
- Sperm Aneuploidy Testing (FISH for 5 chromosomes in> 2000 sperm).
- Genetic Counseling for PGD, PGS or before considering genetic testing.
- PGD for Single Gene Disorders - Standard method.
- PGD for Single Gene Disorders - Karyomapping method.
- HLA-Matching with or without Mutation Detection -Karyomapping method.
- 24-Chromosome Aneuploidy Screening- aCGH method.
- PGD for translocation carriers - aCGH method.
- Products of Conception (POCs) analysis - aCGH method.
- Non-Invasive Prenatal Testing (NIPT).
Genetic testing in embryos
Human embryos are usually cultured for three days (cleavage stage) to five days (blastocyst stage) following in vitro fertilization (IVF). Biopsy for genetic analysis can be performed on days 3 or 5 of embryonic development. More than 50% of cleavage-stage embryos produced in vitro are chromosomally abnormal, increasing to up to 80% in women over 42 years of age. These abnormalities result in low implantation and pregnancy rates in embryos transferred during in vitro fertilization procedures. Although some abnormal embryos arrest between day 3 and 5, most do not, and even at the blastocyst stage more than 40% of embryos are abnormal increasing with advanced maternal age.
Morphological assessment of embryos cannot identify the majority of lethal aneuploidies. The use of preimplantation genetic testing to identify and preferential transfer chromosomally normal embryos improves implantation rates, reduces miscarriages and trisomic offspring, and ultimately leads to an increase in live birth rates
Preimplantation Genetic Screening and Diagnosis (PGS/PGD) are types of genetic tests to determine if an embryo carries extra or missing chromosomes or an inherited disease. These tests greatly reduce the risk of having a child with an aneuploidy or a genetic disease of concern.
Who benefits from preimplantation genetic testing?
IVF patients can improve their chances of a healthy pregnancy with PGS/PGD, especially in the following situations:
- Advanced reproductive age.
- Previous or recurrent pregnancy loss.
- Repeated implantation failure.
- Single embryo transfer.
- Prior child/pregnancy with an inherited disease or chromosomal abnormality.
- Severe male factor infertility.
- Family balancing with gender selection.
Preimplantation Genetic Screening (PGS)
Comprehensive Chromosome Screening: PGS screens for the number of chromosomes in one or a few cells biopsied from embryos produced via IVF. Embryos with the normal number of chromosomes have a better chance of implanting and creating a healthy pregnancy. Following PGS, these embryos can be selected for transfer to the mother's uterus.
Key features of PGS, include:
- Comprehensive chromosome aneuploidy screening (all 23 chromosome pairs, including the sex chromosomes).
- Individual chromosome confidence calls is typically 98% accurate.
- Gender selection is possible.
Preimplantation Genetic Diagnosis (PGD)
Testing for Inherited Diseases: PGD is available for couples identified to be at high risk of having a child with a specific genetic dis¬order. This includes: autosomal recessive diseases, which can be inherited from two unaffected carrier parents (e.g. Thalassemia or Sickle Cell Anemia); autosomal dominant diseases, which can be inherited from an affected parent (e.g. Huntington disease); and X-linked conditions that can be inherited by an affected father or a carrier mother (e.g. Hemophilia and Duchenne Muscular Dystrophy). PGD can test embryos for virtually any specific, single gene mutation, allowing the transfer of unaffected embryos. Most genetic disorders can be tested for, as long as the gene and mutation have been identified in the patient and/or spouse.
Testing for Translocation and Inversion carriers: A carrier of a balanced chromosomal rearrangement has an increased risk of passing on too little or too much genetic material to the embryo, possibly causing infertility, miscarriage, or birth defects and disabilities. Embryos can be tested for any extra or missing chromosome pieces, and those with normal or balanced chromosomal results are selected for transfer to the uterus.
Key features of PGD, include:
- Significantly reduces the risk of miscarriage.
- Available for almost all single gene disorders.
- Tests are tailored to individual patients.
- Corrects for the most common source of PGD misdiagnosis (allele dropout of ADO).
- High accuracy rates (>98%) with rapid results.
- HLA matching is also available.
- Karyomapping is offered to suitable patients, allowing faster time to PGD (shorter work-up time).
- All tests employ DNA fingerprinting for contamination detection.
Benefits of PGS/PGD
PGS/PGD can increase the chance of IVF success by identifying the embryo(s) with best chance to achieve a pregnancy. Using this technology, it is possible to determine chromosome copy number and detect unbalanced chromosome rearrangements as well as inherited diseases in embryos.