A Study to Assess the Tolerability of a Single Dose of STX107 in Adults With Fragile X Syndrome

Inclusion Criteria: * Male subjects 18 to 50 years of age, inclusive. * Molecular documentation of the full fragile X mutation. Exclusion Criteria: * Subjects with a history of seizure disorder who are, in the opinion of the Investigator and Medical Monitor, not currently considered to be well controlled. * Subjects currently being treated with psychoactive medications (including stimulants and anxiolytics). * Subjects with any condition, including alcohol and drug abuse, which might interfere with the conduct of the study, confound interpretation of the study results, or endanger their own well-being. 4. Subjects who plan to initiate or change pharmacologic or non-pharmacologic interventions during the course of the study. * Subjects who, in the Investigator's opinion, might not be suitable for the study