Neuroscientists at the Massachusetts Institute of Technology have taken a major step forward in the quest to find a genetic approach to treating autism.
In a promising new study conducted on mice, researchers showed that "turning on" a specific gene called Shank3 that was mutated in some of the mice could reverse symptoms associated with autism, such as repetitive behaviors and social avoidance.
Roughly 1 percent of people with autism are missing Shank3, usually found in synapses, the building blocks that connect brain cells. Others may have a mutated version. The gene not only helps facilitate communication between neurons in the brain, but is also critical for brain development. Mutations in the gene may also be linked to schizophrenia.
"Genetic mutations play a significant role in autism. In the last 10 years, scientists have identified hundreds of genes that are linked to the cause of autism," said Guoping Feng, a professor of brain and cognitive sciences at MIT and the study's lead author. "Although, in many cases, alterations in multiple genes may contribute to autism, Shank3 is one of the rare cases that this single genetic mutation could cause severe autism."
In the study, which was published Wednesday in the journal Nature, the researchers used genetic engineering to "turn off" the Shank3 protein in mice when they were still embryos. The mice that did not have an active Shank3 gene displayed autism-like symptoms after they were born.
But when the mice were older, researchers "turned on" the Shank3 gene by using an estrogen-blocking chemical called tamoxifen, which they added to the animals' diet. Once this happened, the mice stopped displaying the behavioral symptoms of autism.
When the researchers turned on the Shank3 protein in other, younger mice, the animals exhibited improved motor skills and reduced anxiety (mice that are anxious are usually more isolated from the group and eat less, among other symptoms.)
What does this mean for humans with autism? It's possible that these special gene-editing techniques could help reduce autism symptoms for people with Shank3 gene mutations -- whether they are children or adults.
The optimal time to turn on the gene is still not clear, Feng said, since autism symptoms decreased in both the older and younger mice. But after the gene was turned on in the older mice, researchers found that the density of dendrites -- which are the part of the neurons that attach to the synapses -- increased dramatically in the mice's brains. This suggests the neurons in the older mice's brains became more plastic and better able to adapt to the activated Shank3 gene, resulting in improved symptoms.
"The findings show that some parts of the adult brain are very plastic, and brain function and connections can be modified throughout life," Feng said. "If this is also true in the human brain, it gives some hope that some of the neurodevelopmental defects are reversible, even though early intervention will be more effective."
"Of course, this study is in mice, and we don’t really know to what extent this is true in the human brain," he added.
Still, scientists are excited about the discovery, including Dr. Mathew Pletcher, head of genomic discovery for the research and advocacy organization Autism Speaks. Pletcher called the findings "very significant."
"Folks continually debate this issue of neural plasticity -- whether the adult brain can change, especially when it comes to treating autism," he said. "The common refrain is that any new therapy will not help those who are already diagnosed. This paper tells us that this might not be true."
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