Preclinical Alzheimer disease—the challenges ahead

Pathological changes underlying Alzheimer disease (AD) begin more than 10 years before clinical presentation, and the need for early therapeutic intervention is becoming increasingly recognized. Reisa Sperling and colleagues consider challenges to such an approach—including the difficulty of defining preclinical AD, and ethical issues associated with disclosing information on AD biomarker status to healthy individuals—and discuss possible ways to overcome these hurdles.