A Trial of Metformin in Individuals With Fragile X Syndrome (Met)

Inclusion Criteria: * Subject has Fragile X syndrome with a molecular genetic confirmation of the full FMR1 mutation (\>200 CGG repeats) or the other loss of function mutations of the FMR1 gene (SNVs and deletions of the gene). * Subject is a male or non-pregnant, non-lactating female age 6 through 35 years, inclusive. * Subjects who are capable of becoming pregnant must use an acceptable method of birth control for the duration of the study. Acceptable forms of birth control include abstinence (only for subjects who are not sexually active), intrauterine devices in place for at least 3 months, oral contraceptives, surgical sterilization, or adequate barrier methods. * Subject must have a caregiver (parent, guardian, or other legally authorized representative) who is willing to participate in the whole study. * Subject and caregiver are able to attend the clinic regularly and reliably. * Subject and/or subject's caregiver is able to understand, read, write and speak English or French fluently to complete study-related materials. * For subjects who are not their own legal guardian, subject's caregiver is able to understand and sign an informed consent to participate in the study. * The use of concomitant medication must be stable, in terms of dose and dosing regimen, for at least 4 weeks prior to Screening and must remain stable during the period between first visit (Screening) and the commencement of the study; every effort should be made to maintain stable regimens of allow…