Study of MRM-3379 in Male Participants With Fragile X Syndrome

Inclusion Criteria: * Willing and able to provide signed informed consent/assent. Where local regulations permit inclusion of participants deemed unable to provide informed consent, a legally authorized representative must provide informed consent on the participant's behalf, and the participant must provide assent if applicable. * Male, 13-45 years of age (inclusive) * Weight ≥30 kg and BMI between 18 and 36 kg/m2 (inclusive) at the screening visit * Diagnosis of FXS with a molecular genetic ≥200 CGG repetitions . * Able to perform the PVT and ORRT of the NIH-TCB * Have a consistent caregiver(s) who is willing and able to be present regularly and reliably with the participant * Able to swallow tablets or capsules Exclusion Criteria: History of or current medical condition other than FXS and related issues that would place the participant at higher risk from study participation