Crownlands Observing Progression With Neurons Study

Inclusion Criteria: * Informed consent provided by the participant or, where applicable, Legally Authorized Representative (LAR) or other substitute decision-maker where permitted by applicable law, as described in Section 8.2. * Male or female, age ≥ 55 years at Screening. * Fluency of subject and study partner in English sufficient to complete all cognitive and self-report assessments without interpreter assistance. * Adequate visual and auditory acuity (with correction permitted) sufficient to complete neuropsychological testing. * Not pregnant or lactating. * Medications stable ≥ 4 weeks before screening. * GDS-15 \< 6 (i.e., 0-5 inclusive; no current significant depression). * Available study partner who has known the participant for ≥ 12 months, maintains \~10+ hours per week of in-person or telephone contact, and is willing to attend study visits and complete informant-rated assessments. * Willing to complete olfactory brushing, smell testing, and venous blood draw. * Willing to commit to baseline and follow-up visits across study duration. * In the opinion of the Investigator, able to comply with the protocol-specified visit schedule and procedures for the full study duration. Exclusion Criteria: * Current or active clinically significant neurological disorder (in the opinion of the Investigator) other than the disorders in the study arms, including but not limited to: * Parkinson's disease, dementia with Lewy bodies, frontotemporal dementia, progressive supranucle…