Medical researchers have identified an array of gene mutations linked to autism spectrum disorder (ASD), but they don’t know what actually goes wrong in the brains of those who have the condition.
Researchers from the McGovern Institute for Brain Research at the Massachusetts Institute of Technology have made what they hope is a leap from hypotheticals to observed problems.
Using brain imaging, the researchers showed that the neurotransmitter gamma-aminobutyric acid, or GABA, malfunctions in those with ASD.
“I think it’s a really compelling, provocative study,” Karen J. Parker, Ph.D., the director of the social neurosciences research program at Stanford University School of Medicine, told Healthline. “This is exactly the kind of really forward thinking we need to get traction on this poorly understood disease.”
Parker was not involved in the study, which was published today in the journal Current Biology.
Narrowing the Field of Suspects
GABA is one of several neurotransmitters that researchers have long suspected plays a part in autism.
GABA quiets some neurons’ signals so that the brain can focus on those that seem more relevant at the moment. When we look at an object, for example, the brain receives two images, one from each eye. GABA allows the brain to alternate between seeing one and the other dominantly.
Robertson and her colleagues isolated visual processing to see how GABA worked in study participants with ASD and those without it. They measured neurotransmitters at work in the visual cortex of the brain, where the images from the two eyes first come together.
In the 20 participants with ASD, the GABA was present but didn’t perform its normal function of subduing selective neurons. Glutamate, another neurotransmitter on the list of suspects for autism researchers, worked normally.
“GABA isn’t able to drive vision,” Robertson said. “What it suggests is a dysfunction in the pathway.”
A familiar example of a malfunctioning pathway in the brain is depression. Selective serotonin reuptake inhibitors (SSRIs) allow neurons to use more serotonin as they communicate. The hope is that a drug that changes how neurons use GABA could quiet many, or all, of the symptoms of autism.
The findings are especially promising because GABA is involved in processing other sensory information as well.
“It’s a very important neurotransmitter in the brain,” Caroline Robertson, Ph.D., one of the study’s authors, told Healthline. “It affects almost every piece of information that we process.”
The research participants with more pronounced failures in the GABA pathway were those with more severe forms of autism.
Paving the Way for Autism Drugs
Could drugs that boost GABA functioning in the brain treat the symptoms of autism, the way SSRIs treat depression? This research begins to suggest that they could. Some of the drugs tested for autism target the glutamate pathway, which Robertson’s findings suggest is misguided.
“It’s a very early study, but it suggests that increasing GABAergic signaling would be the lowest hanging fruit to go after,” Parker said.
And there are already a handful of drugs, including arbaclofen, that boost GABA.
Because autism patients are so diverse, researchers are likelier to find a drug that treats some, rather than all, of them, Parker said.
“One of the problems we’ve had with treatment trials is that it’s such a heterogeneous disorder,” she said.
The research was funded with academic grants.