Preimplantation Genetic Testing Considerations: New testing is already available
New technology, testing, and concepts are developed quickly in the genetics field. The latest development is a new type of preimplantation genetic test for polygenic conditions (PGT-P). Preimplantation genetic testing is testing performed on embryos usually to determine the number of chromosomes (PGT-A) or if the embryo has a particular, inherited condition (PGT-M). Our information page on preimplantation genetic testing describes the test and the different types in more detail.
PGT-P is assessing the embryo’s chance of developing conditions that are considered polygenic such as diabetes type 1 and 2, schizophrenia, coronary artery disease, heart attack, hypercholesterolemia, hypertension, breast cancer, testicular cancer, prostate cancer, and some skin cancer.
Polygenic means multiple genes. The conditions listed above are found to be caused by multiple genes. Usually, people are taught about monogenic conditions such as cystic fibrosis and sickle cell disease. A monogenic condition is caused by one (or mono) gene that is not working as it is expected to.
Polygenic conditions can be difficult to test for given there are numerous genes involved. There is a different genetic testing approach to learn someone’s chances to develop these conditions. Testing is not focused on looking for the change to the gene that caused it not to work or its mutation (also known as pathogenic variant). Instead, testing looks at single nucleotide polymorphisms (SNPs) located in multiple genes and determine if the person has a higher than average or lower than average chance at developing the condition.
A single nucleotide polymorphism is a change in the gene that is not considered harmful and does not impact the gene’s ability to carry out the function it is supposed to. SNPs are just variations between people. There have been large studies of people with one of the above conditions such as schizophrenia to figure out if people with schizophrenia have more SNPs in common with each other than compared to individuals without schizophrenia.
The point of the studies is to find SNPs that occur more frequently in the population of people with schizophrenia. Testing will look to see if the person has a lot of those SNPs consistently seen in the population of people with schizophrenia, and predict the individual has a higher than average chance to develop schizophrenia.
It is important to know that the above conditions are not solely caused by these SNPs or genetics for that matter. Environment plays a large role in the chance someone develops one of these conditions. Environment is even more difficult to pinpoint. This is why genetic testing for polygenic conditions will not be able to conclusively state the person will have the condition, rather it may predict if there is an increased or decreased likelihood.
For PGT-P, the information that can be received is whether the embryo is more or less likely to develop polygenic conditions. This testing can be used to better decide which embryo to transfer after it has been determined the embryo likely has the typical number of chromosomes. This testing’s goal is to give the intended parent(s) more information on the potential health of the embryo. This is new testing with caveats and limitations, so it is important to discuss the benefits, risks, and limitations with your healthcare provider. Professional organizations do not yet recommend this testing, and there are ethical concerns of its use.
Resources:
Treff NR, Eccles J, Marin D, Messick E, Lello L, Gerber J, Xu J, Tellier LCAM. Preimplantation Genetic Testing for Polygenic Disease Relative Risk Reduction: Evaluation of Genomic Index Performance in 11,883 Adult Sibling Pairs. Genes (Basel). 2020 Jun 12;11(6):648. doi: 10.3390/genes11060648. PMID: 32545548; PMCID: PMC7349610.
https://www.gimjournal.org/article/S1098-3600(22)00678-5/fulltext
* This blog constitutes general information about genetic testing and medical screening. This blog does not offer or provide medical advice or diagnosis, and nothing in this blog should be construed as medical advice or diagnosis. Do not rely on the information in this blog/article to make medical management decisions. Please consult with a medical professional before making those decisions. Do not delay in seeking professional medical advice if you think you have a medical concern. Do not disregard professional medical advice based on any information received in this blog.
