A Study of Gantenerumab in Participants With Prodromal Alzheimer's Disease

Inclusion Criteria:

• Adult participants, 50-85 years of age
• Participants with prodromal Alzheimer's disease who are not receiving memantine orcholinesterase inhibitors
• Has a study partner who in the investigator's judgement has frequent and sufficientcontact with the participant as to be able to provide accurate information as to theparticipant's cognitive and functional abilities, who agrees to provide information atclinic visits which require partner input for scale completion
• Has had sufficient education or work experience to exclude mental retardation
• Study partner has noticed a recent gradual decrease in participant's memory (over thelast 12 months), which the participant may or may not be aware of
• Screening Mini Mental State Exam (MMSE) score of 24 or above Additional inclusion criteria for sub study:
• Able and willing to travel to PET imaging center and complete the planned scanningsessions
• Past and planned exposure to ionizing radiation not exceeding safe and permissiblelevels

Exclusion Criteria:

• Other prior or current neurologic or medical disorder which may currently or duringthe course of the study impair cognition or psychiatric functioning
• A history of stroke
• A documented history of transient ischemic attack within the last 12 months
• History of schizophrenia, schizoaffective or bipolar disorder
• Currently meets criteria for major depression
• Within the last 2 years, unstable or clinical significant cardiovascular disease (myocardial infarction, angina pectoris) Additional exclusion criteria for sub study:
• Inclusion in a research and/or medical protocol involving PET ligands or otherradioactive agents within 12 months
• Present or planned participation in a research and/or medical protocol involving PETligands or radioactive agents other than study WN25203
• Have planned or are planning to have exposure to ionizing radiation that incombination with the planned administration with study amyloid PET ligand would resultin a cumulative exposure that exceeds local recommended exposure limits