The report was published Feb. 28 in the online edition of The Lancet.
To look for common genetic markers, called nucleotide polymorphisms, that might be risk factors for the five disorders, the Psychiatric Genomics Consortium scanned the genes of more than 33,000 people suffering from these disorders and nearly 28,000 people without such issues. This is the largest study of the genetics of psychiatric illness yet conducted, the researchers said.
Smoller's group found four gene areas that all overlapped with the five disorders, two of which regulate calcium balance in the brain.
These overlapping gene variants appear to increase the risk for bipolar disorder, major depressive disorder and schizophrenia in adults, the researchers said.
Further analysis found that genes governing calcium channel activity in the brain might also be important in the development of all five disorders, autism and ADHD included.
Smoller noted these genetic risk factors may only account for a very small part of the risk driving these disorders, and just how big a share they account for isn't yet known.
So, looking for these genes in an individual now would not be considered a diagnostic tool. "They are not enough to predict any individual's risk. And you might carry all of these variants and never develop a psychiatric disorder," Smoller said.
However, the new findings add to the understanding of these conditions and may help in developing new treatments, he explained.
"It could also change the way we define and diagnose these disorders, based on the biological causes," Smoller said. "Some of the disorders we think of as clinically distinct actually have more of a relationship than we might have thought."
Two experts not connected to the study agreed.
"This is the first genome-wide evidence showing that neuropsychiatric diseases share genetic risk factors,
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