Clinical Study to Assess the Pharmacokinetics, Safety and Tolerability of Single and Multiple Oral Doses of AFQ056 in Children With Fragile X Syndrome (FXS)

Inclusion Criteria: * Genetically confirmed diagnosis of FXS * At Screening and first baseline, vital signs, body weight and body mass index (BMI) must be age-specific within normal ranges. Exclusion Criteria: * Use of any other investigational drug within 30 days or 5 half-lives (whichever is longer) of the investigational drug prior to screening until end of study visit. * History of hypersensitivity to AFQ056 or any mGluR antagonist. * Female patients who are confirmed or suspected to be sexually active. * History or presence of any clinically significant disease of any major system organ class, within the past 2 years prior to screening including but not limited to psychiatric, neurological, cardiovascular, endocrine, metabolic, renal, or gastrointestinal disorders (except for typical features of FXS). * Smokers. * Loss of ≥10% of total blood volume within 8 weeks (or less if required for this age group and/or by local regulation) prior to dosing or longer if required for this age group and/or by local regulation. * Significant illness that did not completely resolve at least four weeks prior to the first baseline visit. * Any abnormal laboratory values at screening or first baseline that are in the opinion of the investigator clinically significant and may jeopardize the safety of the study subject. * Use of (or use within at least 5 half lives before dosing) concomitant medications that are strong/moderate inhibitors or inducers of CYP1A1/2, CYP2C9/19 or CYP3A4 * History or presence of Hepatitis B/C or HIV at screening