This study is a multisite, randomized, double-blind, placebo-controlled, phase 2 study of MG01CI (low and high doses of metadoxine once daily) for 6 weeks compared with placebo in a 1:1 ratio of 60 adolescent and adult subjects with FXS. Following Screening, subjects will be randomized to MG01CI or matching placebo at Baseline (Day 0) and the 6 week Double-blind Treatment Period will begin on Day 1.~The first 4 weeks of the treatment period will be a dose-optimization period, during which the subject's dose of MG01CI or placebo will be optimized. Investigators and subjects will be blinded with regard to whether the subject is taking active drug or placebo. Subjects will be blinded to anticipated dose (low vs high dose), while Investigators will not be blinded to anticipated dose, low dose vs high dose. Every two weeks subjects will receive 2-week supply treatment. A phone follow-up assessment of safety and tolerability will occur during titration after 1 and 3 weeks of treatment; if the investigator has any significant concerns regarding safety and tolerability, the subject will be assessed at the site at an unscheduled visit. All subjects will be assessed at the site after 2 weeks and 4 weeks of treatment.~All subjects will start with either low dose or matching blinded placebo (2 tablets daily). At weekly visits/phone assessments, the investigator will evaluate the dose based upon the investigator's assessment of safety and tolerability. If the subject demonstrates safety or tolerability concerns with the low dose after 1 or 2 weeks of treatment, then the subject will be discontinued. If there are no concerns about safety and tolerability after 2 weeks of treatment, then the dose will be increased to 2 tablets of either high dose of active treatment or placebo. If at high dose there are concerns about safety and tolerability, then the dose will be either kept the same or reduced to low dose for the remainder of the treatment period.~The last 2 weeks of the treatment period will be a dose-maintenance period. During the dose-maintenance period, the subject will maintain his or her optimal dose as determined at the end of the dose-optimization period. A phone follow-up assessment of safety and tolerability will occur after 5 weeks of treatment (after 1 week of dose maintenance). If the investigator has any significant concerns regarding safety and tolerability, the subject will be assessed at the site at an unscheduled visit. The subject will be assessed at the site after 6 weeks of treatment (after 2 weeks of dose maintenance).~There will be a 2-week Follow-up Period after the last dose of study treatment or early termination.
This study is a multisite, randomized, double-blind, placebo-controlled, phase 2 study of MG01CI (low dose and high dose once daily) for 6 weeks compared with placebo in a 1:1 ratio of 60 adolescent and adult subjects with Fragile X Syndrome (FXS). Following Screening, subjects will be randomized to MG01CI or matching placebo at Baseline (Day 0) and the 6 week Double-blind Treatment Period will begin on Day 1.~The first 4 weeks of the treatment period will be a dose-optimization period,~All subjects will start with two daily tablets: low dose metadoxine or matching blinded placebo. At weekly visits/phone assessments, the investigator will evaluate the dose based upon the investigator's assessment of safety and tolerability. If the subject demonstrates safety or tolerability concerns with the low dose after 1 or 2 weeks of treatment, then the subject will be discontinued. If there are no concerns about safety and tolerability after 2 weeks of treatment, then the dose will be increased to high dose or placebo. If at the high dose there are concerns about safety and tolerability, then the dose will be either kept the same or reduced to low dose for the remainder of the treatment period.~There will be a 2-week Follow-up Period after the last dose of study treatment or early termination.