Rodent of the Week: Possible reason autism symptoms sometimes appear later

One of the mysteries of autism is why an infant who seems to be developing normally suddenly regresses after his or her first birthday. This phenomenon, which affects about 25% of children diagnosed with autism, gave rise to the now-discredited hypothesis that immunizations given around the first birthday can cause the disease.

A study published Thursday in mice provides a potential explanation of what happens in the brains of these children.

Researchers at Children's Hospital Boston conducted experiments with mice with a mutation in the Mecp2 gene. This gene is linked to Rett syndrome, an autism-related disorder characterized by developmental loss in children age 12 to 18 months. By using optical tests, the scientists studied the synapses that govern vision. Synapses are the connections between nerve cells that allow messages to be transmitted. The scientists found that, after developing normally at first, the mice began to decline and the strength of their synapses decreased.

The studies suggest that abnormal synaptic function plays a key role in the disease.

"During this last phase of development, you need sensory input to lock down and stabilize the connections," the lead author of the study, Dr. Chinfei Chen, said in a news release. "But the circuit is not getting the right signal to stabilize and continues to look around for connections. . .It's very telling that we see these synaptic abnormalities in the thalamus, which is like a switchboard operation for the brain. A small disruption in the thalamus can radiate to large areas of the cortex."

Understanding the function of the gene could lead to ways to intervene and treat a child with the condition, she said. The researchers are now looking at whether reactivating the Mecp2 gene at different times could improve the brain's organization.

The study was published in the journal Neuron.

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