Safety, Tolerability, and Efficacy of Arbaclofen in 16p11.2 Deletion

This study will enroll male or female subjects, aged 5 to 17 years, who have the 16p11.2 bp4-bp5 deletion. Subjects will be randomized to treatment with either placebo or arbaclofen. Subjects and study staff will be blinded to treatment assignment throughout the study. Both placebo and arbaclofen will be administered as orally disintegrating tablets. Dosing will be flexible, with subjects titrating up to the highest tolerated dose, with maximum permissible dose dependent on age. The treatment period is 16 weeks, after which subjects will taper off of study drug. Subjects will be required to attend multiple study visits, and to communicate with the study staff by phone multiple times throughout the study. The primary efficacy assessment focuses on speech. Secondary and exploratory endpoints assess motor, memory, general cognitive, and other neuropsychological abilities, and brain electrophysiology. The safety evaluations include blood tests, physical exam, and assessment of adverse events. Subjects who complete study participation through the end of the Withdrawal Period may be eligible to enroll in a subsequent open-label study. Dosing will be flexible, with subjects titrating up to the highest tolerated dose, with maximum permissible dose dependent on age. The treatment period is 16 weeks, after which subjects will taper off arbaclofen.