Shared Genes May Link ADHD, Autism, and Depression
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," said Eva Redei, professor of psychiatry at the Feinberg School of Medicine at Northwestern University in Chicago.
She noted that all five of the conditions tackled in the study can share certain clinical features and symptoms, including variation in mood, mental impairments, and even psychosis.
"Therefore, the question is whether the identified shared genetic risk factors are related to the diseases or to the shared clinical symptoms," Redei said. "Shared genetic contribution can identify some key regulators in the brain, and can also help to find new drug targets," she said.
Simon Rego, director of psychology training at Montefiore Medical Center at the Albert Einstein College of Medicine in New York City, agreed that the findings are "an important next step" in understanding mental illness.