GRM5 and fragile X syndrome: A third selective mGluR5 antagonist, basimglurant, was evaluated in a small phase IIa placebo-controlled PK study in adults, a subsequently a larger phase IIb 3-month double-blind, placebo-controlled study in adolescents and adults (age range 14-50 years) (ClinicalTrials.gov Identifier: NCT01517698), and a small phase IIa pharmacokinetic study in youth (age range 5-13 years) with FXS (ClinicalTrials.gov Identifiers: NCT01015430, NCT01750957).