Multicenter, Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Two Year Study to Evaluate the Effect of Subcutaneous RO4909832 on Cognition and Function in Prodromal Alzheimer's Disease With Option for up to an Additional Two Years of Treatment and an Open-Label Extension With Active Study Treatment

This multi-center, randomized, double-blind, placebo-controlled parallel-group study will evaluate the effect of gantenerumab (RO4909832) on cognition and functioning and the safety and pharmacokinetics in participants with prodromal Alzheimer's Disease. Participants will be randomized to receive subcutaneous (SC) injections of either gantenerumab or placebo. Participants who consent to be part of the sub study will undergo positron emission tomography (PET) scanning to assess brain amyloid. The anticipated time on study treatment is 104 weeks in Part 1, with an option for an additional up to 2 years of treatment in Part 2, followed by an open-label extension (Part 3) until July 2020. The dosing for Parts 1 and 2 was stopped after a planned futility interim analysis showed a low probability of meeting the primary outcome measure with the doses studied. The study has converted to open-label to investigate higher gantenerumab doses.