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Some time deep in our evolutionary past, most likely more than once, a significant amount of Neanderthal DNA became mixed in with our own, influencing everything from how we now fight illness to even our appearance.
A new study by researchers from Clemson University and Loyola University in the US now suggests that some of this stolen DNA could be linked to autism spectrum disorder, with specific polymorphisms (or variations) in DNA passed down from Neanderthals being more common in people with autism compared with the general population.
The team analyzed DNA from 3,442 people in total, with and without autism. The association held across black non-Hispanic, white Hispanic, and white non-Hispanic people, though the balance was different in each of those populations.
“It has been estimated that Eurasian-derived populations have approximately 2 percent Neanderthal DNA, which was acquired during introgression events occurring shortly after anatomically modern humans migrated out of Africa,” the researchers write in their published paper.
“With the recent sequencing of multiple archaic human genomes, there has been growing interest concerning the influence of archaic human-derived alleles on modern health.”
Previous research has found Neanderthal DNA shapes certain structures in the brain. Since people with autism have similar neural patterns to each another, the potential role of Neanderthal genes is a relationship the researchers wanted to look at more closely.
The study was able to identify 25 specific polymorphisms that affect gene expression in the brain and which are more common in people with autism. In some cases epilepsy was also involved, a condition that autism is often accompanied with.
For example, a variant in the SLC37A1 gene was shown to be present in 67 percent of white non-Hispanic autistic people with epilepsy, who also had autistic family members. Compare that to 26 percent of autistic people without epilepsy, and 22 percent of people without autism or epilepsy.
It’s not that people with and without autism differ in the amount of Neanderthal DNA they possess, but rather how common certain specific bits of Neanderthal DNA are. What’s more, this varies between individuals – so we’re talking about a very complex picture here.
However, the evidence outlined here is strong enough to warrant investigation in future studies – we’ve still got a lot to learn, both about Neanderthals and their lasting impact on our own physiology and about how autism changes the way the brain functions.
We’re still not sure exactly how Neanderthals and ancient humans originally interacted, for example, or how autism changes brain connections so that people with the condition see the world in a different way.
“This is the first study to provide strong evidence for the active role of a subset of rare, as well as some common, Neanderthal-derived alleles in autism susceptibility in multiple major American populations,” write the researchers.
“We hope this research will lead to further investigation into the ongoing influences of ancient hybridization between Homo sapiens and Neanderthals in brain development, human intelligence, and overall human health, as well as spur work into additional clinical resources for this complex population.”
The research has been published in Molecular Psychiatry.