By Steve Phillips
I have said this before (see post on 12/5/18), but since otherwise intelligent people continue to say that we should pursue human germline gene editing because it can be used as a means of eliminating the transmission of genetic diseases to future generations, I need to say it one more time. There is no reason to expect that editing the genes of human embryos will ever be a practical and effective way to eliminate the transmission of genetic diseases to future generations.
There are several reasons for this. One is that the elimination of genetic diseases in future generations would require the widespread screening of all potential parents to identify everyone who would need to use this technique for it to actually eliminate a genetic disease. There is no reason to think that that will ever be practically possible and if it were possible it would require an extreme limitation on personal liberty (think Brave New World). If genetic diseases cannot be eliminated using this technique, then what those who take this position must be advocating using it as a means for a particular couple to avoid passing on a genetic disease when they know that they are carriers of that disease. There are additional reasons why gene editing will not be practical and effective for that.
If the couple’s sole priority is to eliminate the possibility of passing on the genetic disorder that they carry to a child, the simplest and most effective way to accomplish that is to choose not to conceive children. That means that their desire to have and raise children would need to be fulfilled through adoption, but it is the most effective way of achieving the goal of not passing on the genetic disorder that they carry. If this method is not chosen, the couple must recognize that they are trying to accomplish two goals, both having their own biological child and not transmitting the inherited disease.
For the large majority of couples trying to accomplish both of those goals the method with the least risk and highest likelihood of success would be creating a child through IVF and using preimplantation genetic diagnosis (PGD) to choose an unaffected embryo to be implanted in born. However, this method carries significant moral concerns related to the creation and elimination of embryos who have the genetic disorder. Some might think that this moral concern would be a reason to choose gene editing instead, but it is not that simple. The development of the technique of human embryonic gene editing will require using human embryos as research subjects who will be destroyed as an essential step in the research to establish the effectiveness of this technique. This means that it is not a morally superior technique for those who are concerned about the value of the life of a human embryo.
If a couple would choose to pursue embryonic gene editing for the purpose of having a biological child who did not suffer from a genetic disorder that the couple carries, there are still other problems. If gene editing is being used to transform an embryo with a genetic disorder to an embryo without that genetic disorder, it would be necessary to be able to determine that the embryo actually has the disorder before doing the gene editing. Except for the case of two potential parents homozygous for a recessive disorder, some diagnostic test would be needed. We can currently diagnose many genetic disorders in a multi-cell embryo produced by IVF by using PGD. However, for embryonic gene editing to be effective in completely removing the genes for a genetic disorder and replacing them with normal genes the best time to do the gene editing is at the single cell stage. Even if it is established that gene editing can be done effectively and safely, it is hard to see how we would be able to establish that a single cell human zygote has the genetic disorder prior to treating that single cell.
For all of these reasons, the situations in which human embryonic gene editing would possibly be the preferred means of creating a child without a genetic disorder would be quite rare. It is much more likely that the technique would be used for enhancement.