Map of life expectancy at birth from Global Education Project.

Monday, August 07, 2017

CRISPR critters

I suppose I should say something about the recently announced work of Shoukhrat Mitalipov of Oregon Health and Science University, who claims to have successfully edited the genome of human embryos, in this case to eliminate a disease causing mutation. This work is as yet unpublished and not peer reviewed, but let's assume it is sound.

The technique, which has been much in the news, is called CRISPR/Cas9. I'm not going to go into the technical details here but you can certainly look it up if you are interested, the Wikipedia article is actually reasonably accessible if you have some basic understanding of genetics. But getting under the hood doesn't really matter. This is a genetic system that evolved in prokaryotic cells to combat viral phages. It turns out that it provides a method for precise editing of DNA. Previously, the best they could do was shoot DNA into a nucleus and hope that it would be incorporated somewhere; or they could selectively eliminate genes. This provides a method for editing specific genes.

Before Mitalipov's work, however, attempts to edit genes in human embryos weren't very successful, mostly because the editing didn't work in every cell. The Mitalipov team got in early, however, and they claim to have had potentially clinically useful results. This sounds like good news for people who carry genetic disorders and who want to have children, and it may well be. But it's setting off all sorts of ethical alarm bells.

Obviously you have to make a bunch of embryos and you'll end up destroying most of them. That already happens with in vitro fertilization, however, and the anti-abortion ideologues seem to have pretty much gotten used to it. As I have said many times, they do not really believe that blastocysts are human beings or that zygotes have the moral status of persons. That's just an excuse.

Once we've gotten past that, the obvious question is whether the technique could be used, not only to fix hereditary diseases, but to make designer babies -- with enhanced intelligence, physical capacities, specific talents, whatever their wealthy parents want.

I have a two-part answer to this. The first part is that the border between fixing disease and enhancement is very fuzzy. The boundary between say, just being short and dwarfism, or not being the brightest bulb on the tree and cognitive disability, is essentially arbitrary. So if you don't think enhancement is ethical, you need to decide where to draw the line -- and that's always going to be open to dispute.

Part two is that phenotypes are not generally highly determined by genotypes. While a single mutation can definitively cause certain diseases such as Huntington's or Sickle Cell, for the most part our genetic heritage interacts with our environment to create us. For example, people might be at risk for developing Type 2 diabetes if they consume a particular diet; while many people with the same genetic profile will never get Type 2 diabetes. Do we blame it on their genes or the culinary culture?

Intelligence, musical ability, athletic ability -- all of these are also products of genetic heritage unfolding within a particular environment and personal history. You might have John Coltrane's genes, but if you don't practice, or you could never afford a saxophone in the first place, you won't be John Coltrane. Furthermore, these proclivities for some outcome to occur within some given environment are determined by a whole suite of interacting genes. Scientists have so far found only very small influences on outcomes such as heart disease or IQ from any given gene variant, and even these often turn out to be spurious on further investigation, or might not occur at all in a different environment.

If you tried to maximize the genetic profile for intelligence, it might well be at the cost of some other characteristic, such as longevity or sociability or something else people would be loathe to damage. Or it might only work if the child could be guaranteed some specific form of nurture, and otherwise be affirmatively harmful.

So this is a bridge we won't have to cross for a long time, if we ever get there. Nonetheless I can't say it's impossible that nobody will ever try it. People should probably try to be educated about this issue and we should be talking about it, but there's no need to panic.

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