By Razib Khan | January 7, 2012 10:59 pm

Get ready for PGD, the acronym for preimplantation genetic diagnosis. We don’t really talk about “test tube babies” anymore. It’s “IVF,” and as American as apple pie (OK, perhaps as Israeli as falafel). Here’s the Ngrams result:

It’s just not that big of a deal anymore. But take a look at the order articles in The New York Times. There was a day that peopel were very worried about what “test tube babies” entailed. The end of the world as we know it? If that happened I don’t see anymore complaining.

The Globe & Mail in Canada has a very long piece on PGD, Unnatural selection: Is evolving reproductive technology ushering in a new age of eugenics? I do think it is ushering in a new age of eugenics, though it doesn’t go by that name. Many of the issues I’ve brought up on this weblog, such as the incentive for governments which fund national healthcare to take a deep interest in sifting through the range of future taxpayers and consumers of services, are explored. My basic instinct here is much more libertarian than most people. As a practical matter I’m rather close to a maximalist in terms of the amount of latitude I think parents should be given in selecting the nature of their offspring. But, I’m not a libertarian in an absolute philosophical sense, and I think a broader discussion in a society where the state and majority have coercive power over individuals is warranted.

There are two minor technical angles that I do want to bring up though:

– PGD seems to be ideally tailored already for people who marry their cousins. It would be relatively good at screening for the many recessive diseases which are common in the children of cousins. Also, it might even be able to reduce the fraction of runs of homozygosity through judicious selection. So, in the near future Muslim nations might be major consumers of PGD (Muslims as a whole are moderately anti-abortion, but they take a much more pragmatic line on these issues than the Roman Catholic church).

– PGD for trait selection runs into some statistical genetic difficulties. But, I wonder if perhaps PGD for decreased mutational load might be useful? With high coverage full genome scans could not one ascertain with good precision which genes have been subject to inherited or de novo deleterious mutations? It is generally assumed that loci where there is a major deleterious mutation masked by a normal functional copy still induce some fitness drag on the individual. The range in outcomes in siblings may be part of the natural variation in the mutational load. Parents may be tempted to lop off the asymmetrical-faced end of this.

  • Razib Khan

    also, in raw numbers PGD will be much more ubiquitous in 2020 i predict than IVF is today.

  • Finkelstein

    I suspect the Chinese will beat Muslim nations to PGD. 2 reasons: no religious sentiments to “guide” them, and (usually) they only have one chance to get it right. And… I get the impression that they seem to be getting their science in better and better shape.

  • Razib Khan

    I get the impression that they seem to be getting their science in better and better shape.

    #2, i suppose you think the chinese have more advanced cellphones because there is no such thing as exportation of technology? :-) in any case, probably true that religion will make a difference, but note that the gulf states are funding world class institutions to treat diseases of inbreeding (the people staffing may not be gulf arabs themselves).

  • dev

    “also, in raw numbers PGD will be much more ubiquitous in 2020 i predict than IVF is today.” I’m a bit confused here: As the name implies PGD in the strict sense occurs only in the context of IVF. So are you also predicting that IVF itself will be much more ubiquitous in 2020? If so I’m not disputing that prediction with respect to absolute numbers of IVF pregnancies worldwide; however I’ll note that even apart from cost IVF is not the most convenient procedure in the world as far as women are concerned, requiring as it does a course of injected hormones prior to egg extraction and after implantation of the embryo. There may be a natural ceiling on the percentage of women willing to go through the hassle, even with the promised benefits of PGD.

    Or were you were referring more generally to the use of techniques that can provide genetic information on embryos no matter how they were conceived (e.g., the noninvasive test for Downs Syndrome you recently blogged about)? That I can certainly see as being close to ubiquitous, at least for some countries and some sectors of society.

  • Allen

    Muslims as a whole are moderately anti-abortion, but they take a much more pragmatic line on these issues than the Roman Catholic church

    This is a good point. Even in an Islamic theocracy like Iran, abortion is now permitted for certain cases such as if the mother is endangered or if the child is likely to be severely disabled.

    It’s hard to imagine a genuine Catholic theocratic state permitting abortion like this.

  • Finkelstein

    #3, ah… no… I was referring to and and other such things.

    But quite apart from that, especially in the field of medicine, many in China seem to lack rigour ( Let’s hope that “I only get to have ONE kid” spurs them into spending money on what works.

  • Mustapha Mond

    Falafel is an Arab dish imported into Israel by Yemeni Jews.

  • omar

    Mustapha, I suspect that is what Razib meant…

  • Douglas Knight

    Could you elaborate on cousin marriage? Does cousin marriage produce diseases common enough that they can specifically be screened for? I would expect it to produce unique diseases.

    Actually, you can screen for the unique diseases. If the grandparent has 304 recent mutations [or two grandparents each have 152], then the grandchildren each have 76, 24 of which are common, so an embryo has an expected to have 6 homozygosities, which 64 embryos are enough to eliminate. [I think I’m overestimating the selection power needed here.]

    So it does seem like the power is comparable to the effects of a single cousin marriage, though I’m not sure I’m correctly using the figure of 150-300 that I think I got from Leroi.

  • Douglas Knight

    Also, if the shared grandparent comes from a cousin marriage culture, the grandparent will be inbred and have novel homozygosities that one might like to screen for, though these will not be fatal or probably even crippling, since they have already been observed.

  • Douglas Knight

    I did mess up that last step. But first: “24 of which are common” by which I meant “IN common.” Also, I should have 76/4=19, not 24.

    So there are 19 rare variants that the cousins are both carriers for. For each variant, 1/4 of the embryos will be homozygous, so we have to apply -log(3/4) = 0.4 bits of selection pressure to avoid that particular homozygosity. If we have 6 bits of selection pressure, we can avoid 15 homozygosities, leaving 4 uncontrolled, of which we expect 1. We can probably do a little better by not choosing the 15 loci ahead of time.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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