A Study of Crenezumab Versus Placebo to Evaluate the Efficacy and Safety 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's
judgment : (a) Has frequent and sufficient contact with the participant to be able to
provide accurate information regarding the participant's cognitive and functional
abilities, agrees to provide information at clinic visits (which require partner input
for scale completion), signs the necessary consent form, and has sufficient cognitive
capacity to accurately report upon the participant's behavior and cognitive and
functional abilities; (b) Is in sufficiently good general health to have a high
likelihood of maintaining the same level of interaction with the participant and
participation in study procedures throughout the study duration

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

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

- Evidence of the AD pathological process, by a positive amyloid assessment either on
cerebrospinal fluid (CSF) amyloid beta 1-42 levels as measured on the Elecsys
beta-amyloid (1-42) test system or amyloid positron emission tomography (PET) scan by
qualitative read by the core/central PET laboratory

- Demonstrated abnormal memory function at early screening (up to 4 weeks before
screening begins) or at screening

- Evidence of retrospective decline confirmed by a diagnosis verification form

- Mild symptomatology, as defined by a screening MMSE score of >=22 points and CDR-GS of
0.5 or 1.0

- 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 [MCI])

- If receiving symptomatic AD medications, the dosing regimen must have been stable for
3 months prior to screening. If the participant is taking medical food supplements,
these must also 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

- For enrollment into the China Extension Phase, participants must have residence in
mainland China, Hong Kong or Taiwan and be of Chinese ancestry

Exclusion Criteria:

- Any evidence of a condition other than AD that may affect cognition, including but not
limited to, frontotemporal dementia, dementia with Lewy bodies, vascular dementia,
Parkinson's disease, corticobasal degeneration, Creutzfeldt-Jakob disease, progressive
supranuclear palsy, frontotemporal degeneration, Huntington's disease, normal pressure
hydrocephalus, seizure disorder, or hypoxia

- Seizure history that, in the opinon of the investigator, is likely to results in
cognitive impairment

- History of schizophrenia, schizoaffective disorder, major depression, or bipolar
disorder

- At risk of suicide in the opinion of the investigator

- Presence of significant cerebral vascular pathology as assessed by MRI central reader

- Unstable or clinically significant cardiovascular, kidney or liver disease

- Uncontrolled hypertension

- Screening hemoglobin A1c (HbA1C) greater than (>) 8 percent (%)

- Clinical significant sleep apnea that may be contributing to cognitive impairment.
Sleep apnea, which in the clinical judgement of the investigator is adequately treated
is allowed

- Poor peripheral venous access

- History of cancer except if considered to be cured or If not being actively treated
with anti-cancer therapy or radiotherapy

- Known history of severe allergic, anaphylactic, or other hypersensitivity reactions to
chimeric, human, or humanized antibodies or fusion proteins