These gene variants exist throughout the population of both neurotypical and neurodivergent people, and the individual contribution of any one of these genes to neurodevelopment is negligible. But in combination, they have a significant effect on the wiring of the brain. Bourgeron says that it is not uncommon for one or both parents, who carry some of these gene variants, to display autistic traits such as a preference for order, difficulties in detecting emotions, and being hyperaware of patterns; but unlike their child, these traits do not manifest to such a significant degree that they themselves could be diagnosed as autistic.
Over the last 20 years, autism researchers have devised some ingenious ways of identifying some of these more subtle variants. In the early 2000s, Simon Baron-Cohen, a professor of psychology and psychiatry at the University of Cambridge, and colleagues, devised a test called Reading the Mind in the Eyes. This is intended to assess a person’s ability to detect emotions such as looking playful, comforting, irritated or bored – based on a photograph which shows only the person’s eyes.
The idea is that poorer performance on the test indicates a higher likelihood of a person being autistic. “Autistic individuals have a different way of looking at the face, and they seem to get more information from a person’s mouth,” says Bourgeron. “Neurotypical individuals get more information from the eyes.”
More recently, in partnership with the DNA testing site 23andMe, which agreed to host the Reading the Mind in the Eyes test on their website, Bourgeron and Baron-Cohen were able to gather data on the abilities of more than 88,000 people to read thoughts and emotions from a person’s eyes, and compare this performance with their genetic information. Through this dataset, they were able to identify large groups of gene variants associated with poorer emotion recognition, many of which are thought to be carried by autistic people.
Other research studies have found that common gene variants associated with autism tend to be negatively correlated with empathy or social communication. But they are positively correlated with the ability to analyse and construct systems as well as rules and routines. Most intriguingly, they are also often linked to higher educational attainment, along with greater spatial or mathematical or artistic abilities. “This perhaps explains why these genetic variants, which come from very distant ancestors, have remained in the population throughout human history,” says Geschwind.Â