Autism may be a disorder of hyper-connectivity in the brain, according to a study that found children with the condition have too many synapses, the points where neurons connect and communicate with each other.
The study, published yesterday in the journal Neuron, suggests that a dysfunction in the brain doesn’t prune the neurons during development, as happens in most people. Researchers from Columbia University Medical Center examined tissue from the brains of children who had died, including those with and without autism.
Autism disorders are characterized by indifference to social engagement, communication difficulties and repetitive behaviors. There is no cure or single known cause, though studies have suggested a range of potential biological and environmental starting points. The finding adds a new pathway that may be targeted by a drug, researchers said.
“This is an important finding that could lead to a novel and much-needed therapeutic strategy for autism,” said Jeffrey Lieberman, chairman of psychiatry at Columbia University Medical Center, in a statement. He wasn’t involved in the study.
The researchers examined brain tissue from 26 children and adolescents ages 2 to 20 who had autism, and from 22 more who didn’t. The tissue was from a region of the brain involved in social and communication processes, and implicated in autism. They counted the number of spines extended from the neurons, each of which connect with another neuron by synapse.
By late childhood, researchers found that spine density decreased by 41 percent in the normal brains, compared with 16 percent in the brains of autistic children.
“This deficit may contribute to abnormalities in cognitive functions that humans acquire in their late childhood, teenage or early adult years, such as the acquisition of executive skill such as reasoning, motivation, judgment, language and abstract thought,” the researchers wrote in the study. “Many children diagnosed with autism spectrum disorders reach adolescence and adulthood with functional disability in these skills.”
In the study, researchers turned to mice engineered with a disease similar to autism to see whether they could interfere with the defects in clearing out old cells. They used a drug that worked against a hyperactive protein called mTOR that prevented the brains ability to weed out synapses.
After treatment, the mice showed improved behaviors.
Rapamycin is a drug used to keep the body from rejecting organ and bone marrow transplants. It also carries severe side effects that would probably discourage its use in autistic children. The protein mTOR controls cell growth.
The results showed a direct link between limiting the mTOR protein and the number of synaptic connections, the researchers concluded.