An obvious confound is that older fathers may tend to be geekier than younger fathers, thereby correlating paternal age and autism risk independent of age-related sperm mutation rate.
NYTimes: Older men are more likely than young ones to father a child who develops autism or schizophrenia, because of random mutations that become more numerous with advancing paternal age, scientists reported on Wednesday, in the first study to quantify the effect as it builds each year. The age of mothers had no bearing on the risk for these disorders, the study found.
... The new investigation, led by the Icelandic firm deCODE Genetics, analyzed genetic material taken from blood samples of 78 parent-child trios, focusing on families in which parents with no signs of a mental disorder gave birth to a child who developed autism or schizophrenia. This approach allows scientists to isolate brand-new mutations in the genes of the child that were not present in the parents.
Most people have many of these so-called de novo mutations, which occur spontaneously at or near conception, and a majority of them are harmless. But recent studies suggest that there are several such changes that can sharply increase the risk for autism and possibly schizophrenia — and the more a child has, the more likely he or she is by chance to have one of these rare, disabling ones.
Some difference between the paternal and maternal side is to be expected. Sperm cells divide every 15 days or so, whereas egg cells are relatively stable, and continual copying inevitably leads to errors, in DNA as in life.
Still, when the researchers removed the effect of paternal age, they found no difference in genetic risk between those who had a diagnosis of autism or schizophrenia and a control group of Icelanders who did not. “It is absolutely stunning that the father’s age accounted for all this added risk, given the possibility of environmental factors and the diversity of the population,” said Dr. Kari Stefansson, the chief executive of deCODE and the study’s senior author. “And it’s stunning that so little is contributed by the age of the mother.”
7 comments:
"unresolved causal nexus", indeed.
To play devils advocate on the "old nerd dads" confounder:
1) I would expect geek moms to also be inclined to delay maternity. But“The age of mothers had no bearing on the risk for these disorders, the study found.”
2) We already have a few hits on denovo mutations adding to autism risk. 3) The Icelanders do specify “focusing on families in which parents with no signs of a mental disorder gave birth to a child who developed autism or schizophrenia." 4) The “and Schizophrenia” part seems less confounded by the choice of older paternity. Geeks/borderline autist males probably delay kids, but do sensitive/borderline schizo males as well?
Also, one confounder to the 100k loci calculation:
"Pooling the results of the three studies revealed three genes to be peppered by these de novo mutations."
So, de novo mutations don't hit randomly, and some sites are much more likely than others to be de-novoed.
What if one such site happens to be one of the above genes, and happens to be important for autism and/or schizophrenia?
*
I'm mainly just devils-advocating, though, :-) IMO, it's likely that a ridiculous number of brain-dev loci are vulnerable to autismifying denovo.
I wonder about the robustness of the finding regarding the mother's age. There are only 78 cases in the study; mothers' ages top out in the early forties; wide spousal age spreads nearly always feature older fathers and younger mothers. So this study's failure to falsify age-of-mother effects may not mean as much as the headline suggests.
Another possible confound is the link between father's age and house hold income, and in turn the level of psychiatric care and the diagnosis rate.
What I want to know is why do geeky guys produce more autistic kids when geeks largely come from the high end of the IQ scale and autistics largely come from the low end.
"An obvious confound..."
Obvious only to a moron.
The increase in diagnoses of autism does not reflect any real change.
There is not a real continuum between genuine autism and normal or schizo and normal. Speaking of such a continuum does bring it into existence.
Post a Comment