A Phase 2 Trial of ALN-APP in Patients With Cerebral Amyloid Angiopathy

Inclusion Criteria (sporadic CAA patients): * Is 50 years or older * Has probable CAA per the Boston Criteria Version 2.0 Inclusion Criteria (Dutch-type CAA patients): * Is 30 years or older * Has known E693Q amyloid precursor protein (APP) gene mutation for Dutch-type CAA Exclusion Criteria: * Moderate or severe stage Alzheimer's disease (AD) or significant cognitive impairment (CI) * Has a history of previous clinical intracerebral hemorrhage (ICH) with onset less than 90 days prior to anticipated randomization in the study * Has alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \>3×upper limit of normal (ULN) at Screening * Has estimated glomerular filtration rate (eGFR) \<30 mL/min/1.73m\^2 at Screening * Has recently received an investigational agent * Has had treatment with amyloid-targeting antibody Note: other protocol defined inclusion / exclusion criteria apply