Autism and Synapses Pruning

   Autism refers to a range of conditions characterized by challenges regarding social skills, repetitive behaviors, and difficulties in speech and nonverbal communication. There are many types, caused by different combinations of genetic and environmental influences. For decades scientists have tried to identify the cause of autism, and it seems that we are getting closer to understanding the origin of this disorder.

   Recently, a group of researchers from Columbia University made an extraordinary discovery. They examined the brain tissues of children with autism, and they found an excess of synapses in their connections. A synapse is the structure that permits a neuron to pass an electrical or chemical signal to another neuron. Due to this finding, researchers concluded that it is possible that children with autism may not undergo the regular synapse pruning process during early brain development.


   Throughout childhood neuronal development regular cellular processes get rid of about half of the synapses the child was born with. Having an excessive number of synapses in our brain would prevent it from functioning correctly, since its connections would not be efficient. The impairments seen in children with autism look as if the different parts of the brain were “talking too much”. There had not been any studies on the matter until now,  although for years some speculated that excess synapses could be a sign of autism.

   Dr. Tang, leader of the researcher team,  inspected the number of synapses found in a small section of the cortical tissue. It was evident that children with autism had more synaptic “spines” compared to the control group. This means that these synapses were damaged and they had not been wiped off by a process called autophagy. Autophagy is a natural, regulated, and destructive mechanism of the cell that disassembles dysfunctional components, such as unnecessary connections that may impair the correct functioning of the neuron.


   A protein, mTOR, is the responsible for controlling autophagy process of the neuron. Along with the findings of the Columbia University study, it is been observed that children with autism have an overactive mTOR. As a consequence, this protein prevents the autophagy process from cleaning the area and disposing the damaged synapses in their brains.

   Another important observation made by Dr. Tang was that during late childhood the density in the brain tissue not affected by autism decreased to half. In contrast, there was only a 16 percent decrease in the brains of those who had the condition.

   Dr Sulzer at San Diego University carried out a similar study. He and his team replicated the condition among mice and provided them with a drug, suppressing the mTOR. The result was that there was a balance in the mTOR function and some of the extra synapses were pruned off. Ultimately, this led to reduced display of Autism associated behavior. However, the drug is not yet ready for human consumption. Sulzer said that the fact that changes in behavior were observed suggests that it may be possible to treat autism after a child is diagnosed.

   This new discovery may imply that we are one step closer at understand how autism works and how we can reduce its consequences for the children and their families.