An Efficacy and Safety Study of Atabecestat in Participants Who Are Asymptomatic at Risk for Developing Alzheimer's Dementia

This is a randomized (study drug assigned by chance), double-blind (neither the researchers nor the participants know what treatment the participant is receiving), multi-center (more than one hospital or medical school team work on a medical research study), placebo-controlled, parallel-group study in participants who are asymptomatic and at risk for developing Alzheimer's dementia. The study will consist of a Screening Phase (approximately 90 days), treatment Phase (54 months) and follow-up Phase (7 to 28 days). In treatment Phase eligible Participants will be randomized to receive study drug or placebo once daily for up to 4.5 years. The maximum study duration for a participant will be 58 months. Participants' safety will be monitored throughout the study.