"An increased number of synapses creates miscommunication among neurons in the developing brain that correlates with impairments in learning, although we don’t know how,” senior author Azad Bonni, head of the Department of Neuroscience at Washington University School of Medicine in St. Louis, explained in a statement.
Autism spectrum disorder (ASD) is a common neurodevelopmental condition affecting one in 68 people in the United States. It's generally understood that there is a genetic aspect to ASD (it often runs in families), though environmental triggers may also play a role.
Several genes have been linked to people with autism. Six of these are called ubiquitin ligases and they're responsible for attaching molecular tags called ubiquitins to proteins. Think of these genes as managers, telling their employees (the rest of the cell) how to handle the tagged proteins. Should they be discarded? Should they be taken to another part of the cell?
Some experts believe that individuals with autism have a gene mutation preventing one of their ubiquitin ligases from working correctly. To find out how and why this might be, the scientists at Washington University removed RNF8 (a ubiquitin gene) in neurons in the cerebellum (an area of the brain affected by autism) of young mice. The mice missing the gene developed an excess of synapses, which in turn affected their ability to learn.
Those mice had 50 percent more synapses than their peers, who had their RNF8 gene intact. The scientists then measured the electrical signal in the neurons and found that it was twice as strong compared to those with a normal functioning cell.
ASD affects language, attention, and movement; skills the cerebellum plays an essential role in. To see if the test mice had lower motor skills (a common symptom in people with autism), the researchers trained the mice to associate a puff of air to the eye with a blinking light. One week later, the control group avoided the irritation caused by the puff of air by closing their eyes 75 percent of the time. The test group only did so one-third of the time.
The scientists point out that a mouse that doesn’t shut its eyes when trained doesn’t quite equate to a human with autism (after all, the wiring of autistic brains is highly individualized), and more work is needed to verify the hypothesis. But it does reveal an interesting association between synapses and behavior that could one day lead to treatments.