A father's high intelligence increases the risk of having a child with autism by a third. In addition, this risk depends on the activity of genes associated with microglia, which are more active in men.
Men with high intelligence are 31% more likely to have children with autism, scientists have found. The results were presented at the International Meeting of Autism Research Specialists in San Francisco.
The new findings are consistent with observations from the 1940s, when psychiatrists Leo Kanner and Hans Asperger noted that fathers of children with autism tend to be very smart, and some of them work in technical industries.
A 2012 study in the Netherlands found that more children with autism are found in regions dominated by high-tech manufacturing.
In a new work, assistant professor at the Karolinska Institute Rene Gardner decided to test how reliable the assumptions of Kanner and Asperger are. With colleagues, she collected medical records of 309,803 children whose fathers were drafted into the Swedish army, gaining high scores in the technical part of the Swedish IQ test.
It turned out that in men with IQ of 111 and above, children with autism were born one third more often than those whose IQ was about 100. The study took into account factors such as education level, socioeconomic status of the family, age of parents, etc. …
At the same time, the relationship between the father's IQ and the risk of mental retardation or the development of attention deficit hyperactivity disorder (ADHD) in children was inverse. Thus, for men with an IQ of 75 and below, the risk of developing ADHD in their children was 65% higher than average.
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“Seeing this connection between autism and high paternal intelligence is very interesting,” says Gardner. However, she notes that the overall risk is quite low, and the data still cannot explain what the cause of autism is.
In addition, the work did not include data on mothers. This information was not available: if the researchers received information about the fathers from the army archives, then there was no place to get information about the mothers.
And another study presented at the same conference found that more frequent autism in boys is caused by higher activity of genes associated with microglia, cells that play an important role in brain formation and maintaining contacts between synapses.
The relationship between autism and the number of microglia cells has already been known. In addition, autism is 2–5 times more likely to be diagnosed in boys. And while psychiatrists see the reason for this difference in underdiagnosis of girls, they acknowledge that numerical differences between the sexes do exist.
Neurogeneticist Donna Verling, in search of the biological cause of autism, investigated how gene expression in brain tissue differs in men and women. Her team suggested that the expression of genes associated with autism should be higher in men. The results of the study showed that genes associated with microglia are more active in men.
Grouping the results by age groups showed that the greatest difference in the expression of microglia genes is observed several months before the birth of a child.
According to Verling, it is possible that the higher microglia activity makes boys more sensitive to genes associated with autism. At the same time, girls' less active microglia protect them from the effects of these genes.
These findings are consistent with other studies showing that changes in the brain leading to autism occur before birth. In addition, there are other studies supporting the link between autism and microglia.
For example, in 2010, scientists found that out of 13 brain samples from people with autism, nine had unusually dense, large, or active microglia cells. And in 2014, another team found that mice that had small amounts of microglia early in life displayed behaviors similar to autism, such as unwillingness to interact with other mice.
Alla Salkova