RecruitingPhase 1Drug trialA Study to Evaluate the Safety and Tolerability of ALN-APP in Patients With EOADThe purpose of this study is to evaluate the safety, tolerability, pharmacodynamics (PD) and pharmacokinetics (PK) of a single dose and multiple doses of ALN-APP administered by intrathecal (IT) injection in adult patients with early-onset Alzheimer's Disease (EOAD). Maximum treatment duration for Part A: single dose. Maximum treatment duration for Part B: 12 months.