February 15, 2017
I have a question about this. Why? It seems uneconomical to me. I think there is a far better, more economical way. Correct me if I get anything wrong, because I've been scratching my head about something I read on this.
I assume we are talking about using CRISPR, to "help prevent a baby from inheriting genes known to cause series medical conditions,"
So, consider this process... loosely speaking, (1) harvest eggs from the mother, (2) fertilize them, (3) sequence them to analyze the genetic state, (4) develop/use a CRISPR molecule that can change that problem allele/sequence, (5) do the CRISPR process, (6) sequence them again to make sure it worked right, (7) then implant the zygote. Sounds good to me... except for a two things.
First off, why not instead (1) harvest eggs from the mother, (2) fertilize them, (3) sequence them to analyze the genetic state, (4) select a zygote that is not carrying that gene for cystic fibrosis/Huntington’s/Broka/etc., (7) then implant the zygote. Isn't that much simpler and cheaper?
You have two cases - a medical problem that occurs in the heterozygous condition and in the homozygous condition. One that occurs in the heterozygous case, could be removed by simple selection in one generation, because of only one parent had it, only half of the zygotes would have it and only one quarter of the zygotes if both parents carried it. If it is a condition that occurs only in the homozygous state, then it would take two generations to remove it, but it could be neutralized (made heterozygous) in the first generation.
There is far more reason for this approach... I'm quoting a book here called Genetics For A New Human Ecology - https://www.amazon.com/Genetics-Human.../dp/B01MYCC25Q
The author's perspective is two fold on this. First, CRISPR is not likely to help with larger copy errors such as caused by de novo mutations. Really though he has a far more compelling reason. He makes the point that older parents (mainly the mother) means there will be far more de novo mutations. At the same time there has been a huge reduction in natural selection due to a number of factors including medicine, vaccines and especially reduced family size. He argues for promoting large scale pre-natal artificial selection to replace the natural selection that has been removed. CRISPR could never compensate for the genetic problems that natural selection handles in a normal state... at least not economically practically.
The genetic considerations are very complete, even though he says he carefully wrote it to not be technical, because he points out that this is going to effect everyone. He calls it a change in ecology, which puts it an interesting perspective of adaptation as well. He frames the discussion in moral terms too, which is unusual, but seems like a good idea in this day and age. The book is well laid out and very very short, but quite original and compelling. It's something like an hour read. I think it a very original view and well worth a read.