Genes that increase or reduce the risk of certain mental illnesses and Alzheimer's disease have been identified by an international team of scientists. The researchers said they also pinpointed a number of genes that may explain individual differences in brain size and intelligence.

 

"We searched for two things in this study," senior author Paul Thompson, a professor of neurology at the University of California, Los Angeles David Geffen School of Medicine and a member of UCLA's Laboratory of Neuro Imaging, said in a university news release.

 

"We hunted for genes that increase your risk for a single disease that your children can inherit. We also looked for factors that cause tissue atrophy and reduce brain size, which is a biological marker for hereditary disorders like schizophrenia, bipolar disorder, depression, Alzheimer's disease and dementia," he explained. The researchers said this was the largest-ever brain study to date, according to the release.

 

The team of more than 200 scientists at 100 institutions worldwide measured the size of the brain and its memory centers in thousands of MRI images from more than 21,100 healthy people and screened the participants' DNA at the same time.

 

In people with smaller brains, the researchers found a consistent relationship between subtle differences in the genetic code and smaller memory centers. They also found that the same genes affected the brain in the same ways in people in different populations. The findings may provide new potential targets for drug development.

 

"Millions of people carry variations in their DNA that help boost or lower their brains' susceptibility to a vast range of diseases," Thompson said. "Once we identify the gene, we can target it with a drug to reduce the risk of disease. People also can take preventive steps through exercise, diet and mental stimulation to erase the effects of a bad gene." The researchers also found that a variant in a gene called HMGA2 may affect brain size and intelligence.

 

"We found fairly unequivocal proof supporting a genetic link to brain function and intelligence. For the first time, we have watertight evidence of how these genes affect the brain. This supplies us with new leads on how to mediate their impact,"  

Thompson said.

 

Searching for clues to disorders such as autism and schizophrenia, the researchers also plan to look for genes that influence brain wiring. For that task, Thompson said they will use diffusion imaging, a new type of brain scan that tracks communication pathways among brain cells.   

 

The study was published online April 15 in the journal Nature Genetics.