Five major mental illnesses — autism, attention deficit-hyperactivity disorder, bipolar disorder, major depressive disorder and schizophrenia — appear to share some common genetic risk factors, according to an examination of genetic data from more than 60,000 people worldwide (The Lancet, online Feb. 28).

Researchers in 19 countries examined the genomes of more than 33,000 individuals with one of the disorders and nearly 28,000 controls. They found four regions of the genetic code where variation was linked to all five disorders.

Of particular interest are disruptions in two specific genes. One, CACNA1C, has previously been linked to bipolar disorder and schizophrenia. The other, CACNB2, regulates the flow of calcium in brain cells and is crucial in helping neurons communicate with each other. The researchers posit that the disruption in calcium channel function could be one early pathway that leaves someone vulnerable to developing any of the five disorders, says Jordan Smoller, MD, the study's lead author.

"While these variations are only a small part of the genetic component of these disorders, these findings still point to a shared biology," says Smoller, a professor of psychiatry at Harvard Medical School and Massachusetts General Hospital.

The hope is that these findings will eventually make it easier to diagnose and treat these disorders, says Bruce Cuthbert, PhD, director of the National Institute of Mental Health's Division of Adult Translational Research and Treatment Development.

"We are finally starting to make inroads where we have actual physiological mechanisms that we can target," Cuthbert says. "We can really start to understand the biology instead of having to guess at it."

—Amy Novotney