Test drug eases behavioral symptoms seen in autism
In mice, compound curbs repetitive behaviors and improves sociability
In adult mice, an experimental drug eases two of the core behavioral symptoms of autism spectrum disorders, a new study shows. A single injection of the compound curbed repetitive behaviors and improved sociability, researchers report in the April 25 Science Translational Medicine.
Although it’s too soon to say whether the drug will work in people with autism, similar medicines are already being tested in humans for a related neurological condition known as fragile X syndrome. “This may be a case where you have a mouse finding that can actually lead to human studies in a fairly short amount of time,” says psychiatrist and molecular neuroscientist Jeremy Veenstra-VanderWeele of Vanderbilt University in Nashville.
No currently available drugs treat the core features of autism spectrum disorders — impaired social interactions, communication problems and repetitive behaviors, says study coauthor Jill Silverman of the National Institute of Mental Health in Bethesda, Md. “This is really exciting and worth investigating further because there are no available medicines out there,” she says.
Silverman and her colleagues focused on two kinds of inbred mice with unusual behaviors. One kind of mouse, a strain called BTBR, repetitively grooms, doesn’t interact with other mice normally and squeaks less than others. The second, called C58, jumps again and again, up to 50 times a minute.
About half an hour after receiving a dose of the compound, known as GRN-529, the animals’ pathological grooming and jumping lessened, the team found. Some signs of abnormal social behavior improved, too. Coauthors at Pfizer saw the same results in tests in their lab at Groton, Conn. “For the repetitive behaviors, it was a really strong finding,” Silverman says. “For the social behaviors, it was a more mild effect.”
To Veenstra-VanderWeele, the effects on repetitive behavior are particularly exciting. “We don’t have great treatments for these types of repetitive behaviors,” which often lead to significant distress, he says.
The drug works by interfering with a protein in nerve cells called mGluR5, which detects the brain chemical glutamate. Researchers are becoming increasingly interested in drugs that target mGluR5.
Three companies — Novartis, Roche and Seaside Therapeutics — are testing related compounds in people with fragile X syndrome. About a third of people with the condition have behavioral deficits that meet the criteria for autism spectrum disorders.
“These are extremely exciting times in autism research,” says neuroscientist and cofounder of Seaside Therapeutics Mark Bear of MIT. Because mGluR5-targeting drugs haven’t yet been approved for use in humans, “establishing safety is paramount,” Bear says.
Much more work is needed before the results in mice can be extended to people with autism spectrum disorders. “It’s always important to realize that mouse studies are just that,” Veenstra-VanderWeele says. “Mouse social behavior is much more straightforward than human social behavior. We as people need to learn quite a lot in order to interact socially with our peers. It’s a lot simpler for a mouse.”
