A new drug is showing promise for treating social withdrawal and challenging behaviors associated with fragile X syndrome and some cases of autism.

In a clinical trial of the drug compound STX 209, also known as Arbaclofen, researchers reported Wednesday that both kids and adults alike with fragile X syndrome showed signs of improvement.

Researchers tested the medication as compared to a placebo on 63 people ages 6 to 39 with fragile X between December 2008 and March 2010. Using a behavior rating scale and parent observations, the study published in the journal Science Translational Medicine indicates that the drug yielded gains in socialization and problem behaviors.

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The drug was no more successful than a placebo in treating irritability, however.

“This is the first large-scale study that is based on the molecular understanding of fragile X syndrome and, importantly, suggests that the core symptoms may be amenable to pharmacologic treatment,” said Elizabeth Berry-Kravis of Rush University Medical Center, the lead author of the study.

Fragile X is the most common known cause of inherited intellectual disability and many with the condition also have autism, so finding a treatment may benefit a broad range of individuals.

The research, conducted by scientists at Rush University Medical Center and the University of California, Davis, was funded by Seaside Therapeutics, the maker of the drug being studied.