GRM1 and fragile X syndrome: An increased expression and activity of mGlu1 receptors have been found in the striatum of Shank2 KO mice (Modi et al. 2018), and a correction of repetitive behavior (reduced marble burying) has been reported in the fragile X syndrome mouse model after administration of the mGlu1 negative allosteric modulator, JNJ16259685 (Thomas et al. 2012).