Arbaclofen, a GABA-B agonist that acts presynaptically to decrease glutamate release and mGluR activation, also reverses behavioral phenotypes in the Fmr-1 knockout mouse [40] and showed benefits in social functioning on the ABC-C and VABS in a phase II placebo-controlled crossover study involving 63 patients with FXS [17]. Here, FMR1 is linked to fragile X syndrome.