Sally Weinrich knew something was terribly wrong. On two separate occasions, she forgot to pick up her grandkids from school, and she kept mixing up their names. The 70-year-old retired nursing professor had to face reality. Her worsening symptoms — the forgetfulness and confusion, the difficulties communicating and organizing activities — weren’t just stress or the normal wear and tear of aging. She lived in a matchless setting, on a lake in South Carolina, nestled in a bucolic wood. She swam daily and kayaked three days a week. But even her purposefully healthy lifestyle couldn’t protect her from the darkness she feared most: Alzheimer’s disease.