We recently published an article in Autism Research reporting that autism genes are extremely ancient compared to other genes in the human genome.
Illustration by Alexander Glandien. Courtesy of Spectrum News.
What do I mean by “ancient”? To give a little perspective, the average gene arose during the early chordates, which are organisms that have a notochord. (Chordates also have other defining features but the notochord is most characteristic of this large group.) Chordates include vertebrates such as ourselves, tunicates like sea squirts, and cephalochordates such as the simple fish-like creatures known as lancelets. Chordates first appeared about 530 million years ago. To us as humans who evolved only the last several million years that may seem like a long time ago.
But the average autism gene is even older. Most autism genes evolved during the early bilaterians or even before the development of single-celled fungi like yeast. Bilaterians are animals that have bilaterial symmetry, which is symmetry that occurs along the midline of the body running from head to toe. Bilaterians evolved at least 555 million years ago (mya), if not earlier, and fungi evolved at least 700 mya.
Why is this finding important? Different genes with different functions arose at different periods of evolution. While we don’t currently know the broader evolutionary implication of all of these autism genes, the significant difference in age suggests that they have similar functions and are probably interacting together in an ancient foundational network that’s not just important in brain function but in development of the entire human body. It also suggests that even though the autism spectrum is very genetically and behaviorally heterogeneous, it does have some common roots.
We also found that autism genes are highly conserved (i.e., very sensitive to any kind of mutation), are extremely long, produce very long proteins, these proteins have a larger network of other proteins with which they interact, and the genes contain lots of regulatory elements that help to control gene expression in nuanced ways.
So to recap, this is an ancient group of genes that arose a very long time ago, are conserved across many many organisms suggesting they control very important processes during development, and they’re regulated in many subtler ways, allowing them to function in different cells during different times of development in slightly different ways.
We’re continuing this line of research in the hopes we can better define what these genes are doing as a group in both human development and in many other organisms throughout evolution. In this way, we can better understand what autism is from the biological and evolutionary perspectives. Stay tuned!
(See also Spectrum News for more coverage on our discovery.)