Research that is not quite what it seems

Fertility researchers have traditionally focused on the impact of the mother\’s age on children\’s health, because sons and daughters of older women are known to be at higher risk of Down\’s syndrome and other, rare disorders.

But a landmark study in the Nature journal has shown that most genetic mutations which arise in children are passed down by the father\’s sperm rather than the mother\’s eggs.

Hmm.

Kari Stefansson, senior author of the study by DECODE Genetics, an Icelandic company, said: \”All areas of the human genome were a mutation once upon a time, so all human variety is down to a mutation.

\”But one interesting aspect of this work is it shows us that the classic focus on the age of the mother and the health of the child is not sufficient.

\”The increasing age of the father has a much bigger impact on a child\’s health in a general way. Women are off the hook and we men are on it.\”

Perfectly happy with the idea of the basic research: mutations increase with the age of the man. But I\’m not entirely convinced by the conclusion as it is being presented.

This might be just because I\’m being a pendant but I do think there\’s a point here. As ever, correct me where I err.

As far as I\’m aware, the rate at which conception leads to say, Down\’s syndrome, doesn\’t change over the ageing of a woman. It\’s the rate (umm, chances of?) implantation, the non-rejection by the womb of this flawed foetus, which does change. One description put it in game theoretic terms almost. When young there will be many more chances to conceive a better foetus so rejection of flawed ones is a good use of the huge resources required to bring a pregnancy to term. The older the woman gets the fewer such chances there will be so loosening the standards of rejection makes sense. Worth taking the risk of bring imperfection to term despite the use of those resources as they\’ll not find an alternative foetus to be used on (replace foetus with blastocyst whatever to make sense here).

It is, if you like, analagous to the whole sex thing itself: men continually proffer and women decide whether it happens or not. Conception happens a great deal more than live birth and it\’s the woman (not consciously of course) who decides. And the standards by which that decision gets made alter with age.

Which means that sure, there could well be a rise in mutation rate in sperm as the man ages. But that isn\’t the determinant of a rise in the mutation rate of live births……

11 thoughts on “Research that is not quite what it seems”

  1. “This might be just because I’m being a __pendant__ but I do think there’s a point here. As ever, __correct me where I err__.”

    Did I miss some subtle joke there?

  2. ” there could well be a rise in mutation rate in sperm as the man ages”: there is, and it’s ancient knowledge.

    “But that isn’t the determinant of a rise in the mutation rate of live births……”: I thought it was ancient knowledge that it’s A determinant, but I’m open to correction. Which is more than the poor wee mites are.

  3. Most of the mutations will be straightforward, point mutations, frameshifts and the like, single base-pair stuff. Also most will be effectively recessive and have no direct effect on the child (but potentially on offspring, generations down the line if the mutation ever meets itself).

    Most of these will not be subject to any kind of intrauterine mutation detection and rejection mechanism, even in young, lithe, healthy mothers.

    Down syndrome however is a drastic genetic abberation and indeed is subject to such detection and rejection.

  4. Is it possible that there might be a tendency for males that already carry the appropriate genetic variations (from previous generations) for these disorders to also breed later in life?

    Separately, these mutations will be inherited – so even allowing for natural selection ‘whittling away’ at the deleterious mutations (thanks for the link, dearieme) then a run of late male breeding over a few generations should show some powerfully tragic effects on the kids. Has this ever been noticed?

    Tim adds: The most obvious result of male late breeding is the extension of the human lifespan. For mammals of our sort of size/heart rate etc we’re amazingly long lived. And this has indeed been put down to late male breeders: the genes which allow one to survive to be a late male breeder flowing into subsequent generations.

  5. Doug Young & Tim: My partner breeds pet rats, and is attempting the same thing (breeding older males) to extend their lifespan. The biggest difficulty is that the older males tend to be fat and lazy, and consider their role in breeding to be far too much work to even consider. Draw what conclusions you will from that.

  6. @Tim, so for the sake of posterity the oldest (still capable) males should get the youngest fertile females. Good incentive to get old.

  7. JamesV // Aug 23, 2012 at 11:34 am

    @Tim, so for the sake of posterity the oldest (still capable) males should get the youngest fertile females. Good incentive to get old.
    ———————————————-
    Logic error! ‘should’ doesn’t mean ‘will’.
    As we wrinklies can confirm.

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