Open Label Extension Study of STX209 (Arbaclofen) in Autism Spectrum Disorders

This is an open label extension study enrolling by invitation only to those subjects that have completed Seaside protocols 209AS208 and 22007. Protocol 209AS208, "A Randomized,Double-Blind, Placebo-Controlled, Study of the Efficacy, Safety, and Tolerability of STX209 (Arbaclofen) Administered for the Treatment of Social Withdrawal in Subjects with Autism Spectrum Disorders." Protocol 22007, "An Open Label Extension Study to Evaluate the Safety, Tolerability and Pharmacokinetics of STX209 in Subjects with Autism Spectrum Disorder." This open-label extension will provide data on the following: 1. Evaluate the safety and tolerability of long term use of STX209 (Arbaclofen) 2. Provide supporting pharmacokinetic analyses 3. Assess long term efficacy on social behaviors in subjects with ASD.