This is a multicenter, randomized, double-blind, multiple-dose (two doses), placebo-controlled, parallel-group comparative study followed by an open-label extension study of E2020 in subjects with Down syndrome having regression and disabled ADL. A total of 60 subjects will be randomized to one of three dosing groups (at 1:1:1) to receive 3 mg of E2020, 5 mg of E2020, or placebo for 24 weeks based on their total scores of Body Functionality Checklist, sex, and study site as the allocation factors. This study consists of Pre-randomization Phase (4 weeks), Double-blind Phase (28 weeks), and Extension Phase (24 weeks). The Double-blind Phase includes a 24-week treatment period plus a 4-week transition period.
The purpose of this double-blind, placebo-controlled, comparative study and open-label extension study is to confirm the efficacy and safety of E2020 in subjects with Down syndrome having regression symptoms and disabled activities of daily living.