NCT06384573ACTIVE NOT RECRUITINGPhase 3This is an open label study to treat dominantly inherited Alzheimer's disease (DIAD) mutation carrier participants from the DIAN-TU-001 gantenerumab Open Label Extension (OLE) period with lecanemab to determine the effects of amyloid removal on age of onset and clinical progression compared to external controls, if amyloid plaque as measured by amyloid PET can be fully removed in DIAD, and the effects of amyloid removal on biomarkers of disease progression.
Key Inclusion Criteria: * Previously participated in the DIAN-TU-001 gantenerumab OLE period. * Willing to participate in ongoing anti-amyloid therapy with informed consent by participant or legally authorized representative. * People of childbearing potential (POCBP), if partner is not sterilized, must agree to use highly effective contraceptive measures (e.g., hormonal contraception, intra-uterine device, sexual abstinence, vasectomized partner) from Consent (V1) until five (5) halflives after last dose of any study drug. Refer to the study procedures manual for acceptable methods of contraception. * Co-enrollment in the DIAN Observational Study (DIAN Obs, NCT00869817) and is willing to complete DIAN Obs procedures and assessments. * Able to undergo safety MRI scans as required. * Vascular access adequate for study drug administration and safety monitoring. Key Exclusion Criteria: * Has any significantly increased risks associated with amyloid-related imaging abnormalities characterized by edema/effusion (ARIA-E), ARIA characterized by microhemorrhage (ARIA-H MCH) or superficial siderosis (ARIA-H SS) and vascular factors reviewed by the medical monitoring team. Risks to be reviewed include: 1. History of recurrent ARIA-E (2 or more episodes regardless of location). 2. More than 20 ARIA-H MCH. 3. More than one area of ARIA-H SS. 4. More than 2 lacunar infarcts or stroke involving a major vascular territory. * Requiring full anticoagulation or on high dose or dual antiplatelet therapy (daily aspirin 325 mg or less allowed). * History of macrohemorrhages \>1 cm. * Intolerance for lecanemab. * Pregnancy. * Breastfeeding. * Uncontrolled medical condition that is life threatening or precludes interpretation of AD. * Uncontrolled blood pressure including mean arterial pressure exceeding 97 mm Hg. * Uncontrolled seizure disorder. * Ongoing auto-immune condition, bleeding diathesis, or neutropenia (platelets lower than 50,000) major depression or psychiatric condition. * Exposure to other AD investigational agents within the past six months, or five half-lives from Visit 2 (Entry Visit) whichever is longer. * Active cancer/malignancy that could interfere with study evaluations.