A new study provides clues into how the potential for schizophrenia may have arisen in the human brain and, in doing so, suggests possible treatment targets. It turns out psychosis may be an unfortunate cost of our big brains—of higher, complex cognition.
The study, led by Mount Sinai researcher Dr. Joel Dudley, proposed that since schizophrenia is relatively prevalent in humans despite being so detrimental—the condition affects over 1% of adults—that it perhaps has a complex evolutionary backstory that would explain its persistence and exclusivity to humans. Specifically they were curious about segments of our genome called human accelerated regions (HARs).
HARs are short stretches of DNA that while conserved in other species, underwent rapid evolution in humans following our split with chimpanzees, presumably since they provided some benefit specific to our species. Rather than encoding for proteins themselves, HARs often help regulate neighboring genes. Since both schizophrenia and HARs appear to be for the most part human-specific, the researchers wondered if there might be a connection between the two.
To find out, Dudley and colleagues used data culled from the Psychiatric Genomics Consortium, a massive study identifying genetic variants associated with schizophrenia. They first assessed whether schizophrenia-related genes sit close to HARs along the human genome—closer than would be expected by chance. It turns out they do, suggesting that HARs play a role in regulating genes contributing to schizophrenia. Furthermore, HAR-associated schizophrenia genes were found to be under stronger evolutionary selective pressure compared with other schizophrenia genes, implying that the human variants of these genes are beneficial to us in some way despite harboring schizophrenia risk.
“The ultimate goal of the study was to see if evolution may help provide additional insights into the genetic architecture of schizophrenia so we can better understand and diagnose the disease,” says Dudley.
But the findings also offer a possible explanation for why schizophrenia arose in humans in the first place, and why it doesn’t seem to occur in other animals. “It’s been suggested,” Dudley explains, “that the emergence of human speech and language bears a relationship with schizophrenia genetics, and incidentally also autism. Indeed, language dysfunction is a feature of schizophrenia. There seems to be an evolutionary story connecting schizophrenia risk with intelligence.”
This piece of information is an excerpt from Scientific American.
The original publication can be accessed here.