A Study to Evaluate the Pharmacodynamic (PD) Effects of Once Weekly Administration of Gantenerumab in Participants With Early Alzheimer's Disease (AD)

Inclusion Criteria

• •Probable Alzheimer's Disease (AD) dementia or prodromal AD.
• •Availability of a reliable study partner (non-professional caregiver) who accepts to participate in study procedure throughout the study duration
• •The participant should be capable of completing all aspects of study assessments including MRI, clinical genotyping, and PET imaging, either alone or with the help of the study partner (non-professional caregiver).
• •Adequate visual and auditory acuitysufficient to perform the neuropsychological testing (eye glasses and hearing aids are permitted).
• •Evidence of AD pathological process, as confirmed by amyloid PET scan by qualitative read by the core/central PET laboratory.
• •Prodromal or mild symptomatology, as defined by a screening Mini-Mental State Examination (MMSE) score \>/=22 and Clinical Dementia Rating global score (CDR-GS) of 0.5 or 1.0, as well as a clinical dementia rating (CDR) memory domain score \>/=0.5.
• •If the participant is receiving symptomatic AD medications, a stable dosing regimen for at least 3 months prior to screening and until start of study treatment.
• •Agreement not to donate blood or blood products for transfusion for the duration of the study and for 1 year after final dose of study drug.
• •Agreement not to participate in other research studies for the duration of this trial, unless these are related Roche-sponsored non-interventional studies.
• •For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods hat result in a failure rate of \< 1% per year during the treatment period and for at least 16 weeks after the final dose of study drug.