A Study Evaluating the Efficacy and Safety of Crenezumab Versus Placebo in Participants With Prodromal to Mild Alzheimer's Disease (AD).

Inclusion Criteria:

• Weight between 40 and 120 kilograms (Kg) inclusive

• Availability of a person (referred to as the "caregiver") who in the investigator'sjudgment:

• Has frequent and sufficient contact with the participant to be able to provideaccurate information regarding the participant's cognitive and functional abilities,agrees to provide information at clinic visits (which require partner input for scalecompletion), signs the necessary consent form, and has sufficient cognitive capacityto accurately report upon the participant's behavior and cognitive and functionalabilities

• Fluency in the language of the tests used at the study site

• Adequate visual and auditory acuity, in the investigator's judgment, sufficient toperform the neuropsychological testing (eye glasses and hearing aids are permitted)

• Evidence of the AD pathological process, by a positive amyloid assessment either oncerebrospinal fluid (CSF) amyloid beta 1-42 levels as measured on the Elecsysbeta-amyloid(1-42) test system or amyloid PET scan by qualitative read by thecore/central PET laboratory

• Demonstrated abnormal memory function at screening (up to 4 weeks before screeningbegins) or screening (FCSRT cueing index =<0.67 AND free recall =<27)

• Screening mini mental state examination (MMSE) score of greater than or equal to (>=) 22 points and Clinical Dementia Rating-Global Score (CDR-GS) of 0.5 or 1.0

• Meets National Institute on Aging/Alzheimer's Association (NIAAA) core clinicalcriteria for probable AD dementia or prodromal AD (consistent with the NIAAAdiagnostic criteria and guidelines for mild cognitive impairment (MCI)

• If receiving symptomatic AD medications, the dosing regimen must have been stable for 3 months prior to screening

• Participant must have completed at least 6 years of formal education after the age of 5 years

Exclusion Criteria:

• Any evidence of a condition other than AD that may affect cognition such as otherdementias, stroke, brain damage, autoimmune disorders (e.g. multiple sclerosis) orinfections with neurological sequelae.

• History of major psychiatric illness such as schizophrenia or major depression (if notconsidered in remission)

• At risk of suicide in the opinion of the investigator

• Any abnormal MRI findings, such as presence of cerebral vascular pathology, corticalstroke, etc or inability to tolerate MRI procedures or contraindication to MRI

• Unstable or clinically significant cardiovascular (e.g., myocardial infarction),kidney or liver disease

• Uncontrolled hypertension

• Screening hemoglobin A1c (HbA1C) >8%

• Poor peripheral venous access

• History of cancer except: If considered to be cured or If not being actively treated with anti-cancer therapy orradiotherapy

• Known history of severe allergic, anaphylactic, or other hypersensitivity reactions tochimeric, human, or humanized antibodies or fusion proteins