A positive biomarker result is necessary but not sufficient. The two FDA-approved disease-modifying drugs — Leqembi and Kisunla, which is also designed to target amyloid — are approved for people in the early stages of Alzheimer’s disease who test positive for amyloid buildup. In some countries, people who carry two copies of the ApoE4 gene are excluded from eligibility because they have a higher risk of side effects, including brain swelling and bleeding.