Inclusion Criteria:  Subject has completed the Week 26 visit of either of the two blinded parent studies (ATH-1017-AD-0201 or ATH-1017-AD-0202). Reliable and capable support person/caregiver who is willing to accept responsibility for supervising the daily treatment or, if required, administering study drug. Subject capable of giving signed informed consent, or by a legally acceptable representative. Subjects must be in generally good health. Male subjects and their partners must agree to continue to use a double-barrier method of contraception during the study, including the follow-up period, unless the partner is not of childbearing potential.  Exclusion Criteria:  Subject has experienced a serious adverse event during the parent study, which could present an increased safety risk during the open label extension. New diagnosis of severe major depressive disorder even without psychotic features. Any subject with formalized delusions or hallucinations. Significant suicide risk.  Newly-diagnosed malignant tumor, except for the following conditions that are stable in the judgement of the investigator:  Adequately treated squamous and basal cell carcinoma, or squamous and basal cell carcinoma in situ Prostate carcinoma in situ