Safety, Tolerability and Efficacy Study of STX209 in Subjects With Fragile X Syndrome

A Double-Blind, Placebo-Controlled, Crossover, Flexible-Dose Evaluation of the Efficacy, Safety and Tolerability of STX209 in the Treatment of Irritability in Subjects With Fragile X Syndrome

The study objective is to explore the efficacy, safety and tolerability of STX209 for treatment of irritability in subjects with FSX. We hypothesize that STX209 will improve irritability and other typical problem behaviors associated with fragile X syndrome. We also hypothesize that STX209 will be safe and well tolerated.

Inclusion Criteria:

• Male or female subjects 12 to 40 years of age eventually expanding to 6 years of age
• Molecular documentation of the fragile X mutation.
• Clinical Global Impression - Severity (CGI-S) rating for problem behavior of moderate or higher at screening and at Visit 1
• An Aberrant Behavior Checklist (ABC-C) Irritability Subscale score >12 and at least 3 items on the Irritability Subscale rated at least moderate or above.
• Current treatment with no more than three psychoactive medications, including anti-epileptics.
• Current pharmacological treatment regimen has been stable for at least 4 weeks.

Exclusion Criteria:

• Subjects with a history of seizure disorder who are not currently receiving treatment with antiepileptics.
• 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. This includes, but is not limited to impairment of renal function, evidence or history of malignancy or any significant hematological, endocrine, cardiovascular, respiratory, hepatic, or gastrointestinal disease.
• Subjects who plan to initiate or change pharmacologic or non-pharmacologic interventions during the course of the study.
• Subjects who are currently receiving treatment with racemic baclofen.
• Subjects currently treated with vigabatrin or tiagabine.
• Subjects taking another investigational drug currently or within the last 30 days.