In the largest study of its kind, researchers studying brains affected by autism found a common pattern: Widespread activation of brain immune cells that produce inflammation.
The investigators conclude that the brain inflammation likely resulted from, rather than caused, autism. Still they urge further research to see if new treatments that calm brain inflammation might ease autism symptoms.
"There are many different ways of getting autism, but we found that they all have the same downstream effect," says study author Dan Arking, of Johns Hopkins’ McKusick-Nathans Institute for Genetic Medicine. "What we don't know is whether this immune response is making things better in the short term and worse in the long term."
The study, which appears today in Nature Communications, involved donated post-mortem brain tissue from Autism Speaks Autism Tissue Program. The program is now part of Autism BrainNet, a collaboration between Autism Speaks and the Simons Foundation.
Learn more about Autism BrainNet here.
A widespread pattern of immune-cell activation
The investigators compared gene expression in 72 brains, 47 of which came from children and adults affected by autism.
Specifically, they looked at gene expression in brain immune cells called microglia. When activated, microglia destroy microbes and unhealthy cells in the brain. Activated microglia are also associated with brain inflammation that can harm healthy tissue.
In the brains not affected by autism, the researchers found gene-expression patterns indicating the microglia were in a largely resting (noninflammatory) state.
By contrast, they found a pattern of widespread microglial activation in the brains affected by autism. These findings add to the growing body of research showing links between autism and brain inflammation.
Besides fighting infections and cleaning away damaged cells, microglia play an important role in pruning away excess brain-cell connections – called synapses – during brain development. Previous research has suggested that interference with this process can lead to autism. (See Brain Study Suggests that Autism Involves Too Many Synapses.)
Along these lines, the Johns Hopkins researchers found chemical evidence of differences in synaptic function between the brains affected by autism and those that were not. They called for further research aimed at understanding these differences.
Autism Speaks’ Paul Wang, the organization’s senior vice president for medical research, expressed appreciation for the generosity of families who made the tissue donations involved in this and other autism brain studies.
“There’s no substitute for direct study of the brain, and these precious donations make it possible,” Dr. Wang says. Learn more about enrolling yourself or your family in Autism BrainNet here.