Safety and Efficacy Study of Gantenerumab in Participants With Early Alzheimer's Disease (AD)

• Meets National Institute on Aging/Alzheimer's Association (NIAAA) core clinical criteria for probable AD dementia or prodromal AD (consistent with the NIAAA diagnostic criteria and guidelines for mild cognitive impairment)
• Evidence of the AD pathological process, as confirmed by CSF tau/A-beta42or amyloid PET scan
• Demonstrated abnormal memory function
• MMSE score greater than or equal to 22 (≥ 22)
• Clinical dementia rating-global score (CDR-GS) of 0.5 or 1.0
• Availability of a reliable study partner who accepts to participate in study procedures throughout the 2 years duration of study
• If receiving symptomatic AD medications, the dosing regimen must have been stable for 3 months prior to screening and until randomization
• For enrollment in the China extension, patients must have residence in mainland China, Hong Kong, or Taiwan and be of Chinese ancestry
• For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods

• Any evidence of a condition other than AD that may affect cognition
• History of schizophrenia, schizoaffective disorder, major depression, or bipolar disorder
• History or presence of clinically evident systemic vascular disease that in the opinion of the investigator has the potential to affect cognitive function
• History or presence of clinically evident cerebrovascular disease
• History or presence of posterior reversible encephalopathy syndrome
• History or presence of any stroke with clinical symptoms within the past 12 months, or documented history within the last 6 months of an acute event that is consistent with a transient ischemic attack
• History of severe, clinically significant CNS trauma
• History or presence of intracranial mass (e.g., glioma, meningioma) that could potentially impair cognition
• Presence of infections that affect brain function or history of infections that resulted in neurologic sequelae
• History or presence of systemic autoimmune disorders that potentially cause progressive neurologic disease with associated cognitive deficits
• At risk for suicide in the opinion of the investigator
• Alcohol and/or substance abuse or dependants in past 2 years
• Relevant brain hemorrhage, bleeding disorder and cerebrovascular abnormalities
• Any contraindications to brain MRI
• Unstable or clinically significant cardiovascular, kidney or liver disease
• Uncontrolled hypertension
• Unstable or clinically significant cardiovascular disease
• Abnormal thyroid function
• Patients with evidence of folic acid deficiency

Exclusion for Open-Label Extension (OLE):

• Discontinued from study treatment during the double-blind treatment period
• Received any other investigational medication during the double-blind treatment period or after the end of double-blind treatment
• Participation in the OLE deemed inappropriate by the investigator
• Presence of ARIA-E findings at the Week 116 MRI scan