Older fathers linked to autism and schizophrenia in children
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, 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.”
Dr Stefansson said that it made sense that de novo mutations would play a significant role in brain disorders. At least 50 per cent of active genes play a role in neural development, so random glitches are more likely to affect the brain than other organs, which have less exposure.
These kinds of mutations may account for between 15 and 30 per cent of cases of autism, and perhaps schizophrenia, some experts said. The remainder is likely a result of inherited genetic mutations and environmental factors.
Dr Stefansson and other experts said an increase in the average age of fathers has most likely led to more cases of autism. Unlike other theories proposed to explain the increase, such as vaccination, it is backed by evidence scientists agree is solid.
But this by itself does not explain the overall increase in diagnoses. In the US, the birth rate of fathers aged 40 and older has increased by more than 30 per cent since 1980 but the diagnosis rate has jumped tenfold, to one in 88 eight-year-olds. And it is not clear whetherif the rate of schizophrenia diagnosis has increased at all in that time.
“You are going to have guys who look at this and say, ‘Oh no, you mean I have to have all my kids when I’m 20 and stupid?’ ” said Evan E Eichler, professor of genome sciences at the University of Washington. “Well, of course not. You have to understand that the vast majority of these mutations have no consequences, and that there are tons of guys in their 50s who have healthy children.”
– (New York Times)