Multiple Dose Study of BIIB037 in Subjects With Prodromal or Mild Alzheimer's Disease.

Inclusion Criteria:

• Subjects must meet criteria for Prodromal Alzheimer's Disease (AD) or Mild Alzheimer's Disease (AD):

  1. Mini Mental State Examination (MMSE) score between 20-30,
  2. Clinical Dementia Rating Scale (CDR) score of 0.5 or 1.0, and
  3. a free recall score of lesser or equal to 27 on the Free and Cued Selective Reminding Test (FCSRT) for prodromal Alzheimer's Disease (AD).
• Subjects must have a positive florbetapir positron emission tomography (PET) amyloid scan.
• Subjects must consent to apolipoprotein E (APOE) genotyping.
• Apart from clinical diagnosis of Alzheimer's Disease (AD), subject must be in good health.
• Must have a reliable informant or caregiver.

Inclusion Criteria for the Long Term Extension (LTE), candidates must meet the following eligibility criteria at Week 56:

1. Subject must have completed the placebo-controlled portion of the study. Subject must have received 11 or more doses, and must not have missed more than 2 consecutive doses; subjects who don't meet this criteria can only enter the Long Term Extension (LTE) upon Sponsor's approval.
2. Mini Mental State Examination (MMSE) score >10 at the Week 54 visit.
3. Subject (or subject's legal representative) has the ability to understand the purpose and risks of the study and provide signed and dated informed consent (or assent) and authorization to use protected health information (PHI) in accordance with national and local subject privacy regulations.
4. Must be ambulatory.

Exclusion Criteria:

• Any medical or neurological condition (other than Alzheimer's Disease) that might be a contributing cause of the subject's cognitive impairment.
• Have had a stroke or Transient Ischemic Attack (TIA) or unexplained loss of consciousness in the past 1 year.
• Clinically significant psychiatric illness in past 6 months.
• Seizure in the past 3 years.
• Poorly controlled diabetes mellitus.
• History of unstable angina, myocardial infarction, chronic heart failure, or clinical significant conduction abnormalities within 1 year prior to Screening.
• Indication of impaired renal or liver function.
• Have human immunodeficiency virus (HIV) infection.
• Have a significant systematic illness or infection in past 30 days.
• Brain MRI showing evidence of acute or sub-acute micro or macrohemorrhage, greater than 4 microhemorrhages, cortical infarct or greater than one 1 lunar infarct.
• Any contraindications to brain MRI or positron emission tomography (PET) scans.
• Negative positron emission tomography (PET) scan with any amyloid-targeting ligand within 48 weeks of Screening.
• Clinically significant 12-lead electrocardiogram (ECG) abnormalities.
• Alcohol or substance abuse in past 1 year.
• Taking blood thinners (except for aspirin at a prophylactic dose or less)
• Have changes in medications or doses of medication in past 4 weeks.

Exclusion Criteria for Long-term Extension:

Any medical or psychiatric contraindication or clinically significant abnormality that, in opinion of the Investigator, will substantially increase the risk associated with the subject's participation in and completion of the study.