<qa>  What is the total length of the double-blind study?Patients who complete all 24 weeks of the double-blind study E2020-E044-316 NCT00165815 will be eligible for the open label extension study. Patients and caregiverstudy partner will need to provide additional written informed consent to participate in the open label extension study. Safety and tolerability will be assessed after 4, 8 12, 24, 36 and 52 weeks. Cognition, Global Clinical Function, Activities of Daily Living, and Behaviour will be assessed after 24, and 52 weeks. 