PGS and PGT-A: Why You Should Be Cautious About Genetic Testing
Dr. Gleicher explains the importance of understanding the different kinds of genetic testing and how they can affect your fertility chances. Despite the frequency of genetic testing available today, we should all be careful about how we use our genetic material.Want to Consult Dr. Gleicher?
Hello, I’m Norbert Gleicher, MD and I’m the Medical Director and Chief Scientist here at CHR. We have decided that this month it’s important to try to educate our public a little better about genetic testing and the reason for that is that genetic testing seems to be exploding. It’s everywhere. You can’t turn on your TV without seeing advertisements that are trying to entice you to send in your blood or your buccal smears to get your “genetic testing”– whether it is for the detection of risk for certain diseases or whether it is simply for ancestry testing.
What is important for everybody to understand is that when you send in your blood or when you send in your buccal smear you’re sending in your DNA and you’re making your DNA available to whatever company is providing you with those test results. And you indeed reveal yourself through your DNA and you reveal yourself to such an intimate degree that there’s simply no comparison with anything else. As we have noted in our videos before, that obviously creates significant risk, requires obviously a high degree of confidentiality and trust on your part if you are willing to share your DNA for these purposes with various entities.
In infertility, genetic testing has also in recent years greatly expanded and that also applies to us here at CHR. We have been testing for chromosomal abnormalities for many decades( like most fertility centers) and we have been doing that because certain chromosomal abnormalities can be a very rare cause for repeated pregnancy loss. And therefore, especially in couples who come to our center because they have had repeated miscarriages, chromosomal testing (the verification that the number and makeup of your chromosomes are normal) has been an essential part of diagnosis in couples with repeated miscarriages.
Chromosomal testing has also been important in cases of repeated miscarriages in testing the products of conception because when a couple has repeated miscarriages, you obviously want to know the cause. And therefore, testing the products of conception for chromosomal abnormalities can help you in determining whether a miscarriage is an unimportant random event (unimportant in the sense that it has no predictive value for future pregnancies) or whether there is a chromosomal abnormality present in one of the two parents that indeed increases the risk for chromosomal abnormalities in the offspring and therefore the risk for increased chances of having a spontaneous miscarriage.
But, genetic testing does not only involve chromosomal testing in infertility practice. Increasingly, we are also testing patients for their DNA. And we are not doing it to test your ancestry or even to test your alleged talents, but we do it with the idea of trying to prevent the birth of babies with genetic diseases. There is a large number of inherited diseases, which are inherited because one little area of DNA in either mom and/or father are mutated. And we have talked elsewhere in our video series on genetics about the fact that there are recessively inherited single gene diseases and there are dominantly inherited and sex linked inherited diseases.
All of these diseases are now very easily and cheaply tested. And indeed the reason that it is so cheap to test large numbers of these genetic diseases, more and more of these tests are done for single gene diseases that are so rare that it almost doesn’t make any sense to test for them. Yet, they’re still being tested because they are now packaged. And so, whenever we test our patients, or for that matter even egg donors, there’s hardly a case where a patient isn’t found to be a carrier for one, two, or three mutations and then the partner needs to be tested and usually what we find is that both may be carrying certain mutations for recessive diseases, but since they’re not the same there’s really no risk for offspring. But then there are those rare cases where indeed both parents are carriers for the same recessive mutation and that creates a one-in-four (25%) risk of having an affected child.
And that’s the principal purpose why we do testing in infertility because we obviously want to help our patients have healthy children. If such a case arises, in other words if there is a case, where there is a significant risk that a pregnancy that we are creating through fertility treatment may carry a genetic disease (a mutation that causes a genetic disease), we now have the tools to usually test embryos for that mutation. And this testing is called pre-implantation genetic testing for mutations. This is a very important testing opportunity because it really allows us with high accuracy to determine whether embryos that are considered especially high risk (and again that means usually either 25 or 50 percent), whether these embryos are affected or are not affected. And then that obviously gives us the option of not transferring those embryos that are affected.
This is really the only, and I repeat, the only form of pre-implantation genetic testing of embryos that we here at CHR strongly support because this really offers a very dramatic potential health benefit. All other forms of embryonic testing (for so-called “genetic testing”) we are quite skeptical about– especially what is called or what was called PGS (pre-implantation genetic screening) and is now called a PGTA (pre-implantation genetic testing for aneuploidy). In contrast to the testing that I’ve just mentioned where we are looking whether embryos are genetically affected by a disease, PGTA tests for chromosomal abnormalities. Again, the difference I referred to earlier, the other form of genetic testing.
This testing for chromosomal abnormalities in embryos, in our opinion here at CHR, is highly inaccurate and we therefore do not recommend it. So, there is more and more genetic testing going on in fertility centers but you better understand what the advantages and disadvantages are for the various forms of genetic testing before you entrust anybody with your own genetic bodily materials. Be careful. Thank you very much.