Tau Positron Emission Tomography (PET) Longitudinal Substudy Associated With: Study of Crenezumab Versus Placebo in Preclinical Presenilin1 (PSEN1) E280A Mutation Carriers in the Treatment of Autosomal-Dominant Alzheimer's Disease

Crenezumab will be administered subcutaneously (every 2 weeks) or IV (every 4 weeks) for at least 260 weeks.

Placebo matched to crenezumab will be administered subcutaneously (every 2 weeks) or IV (every 4 weeks) for at least 260 weeks.

IV \[\^18F\]GTP1 will be administered up to three times. The first primary \[\^18F\]GTP1 tau PET scan will occur during any visit in the main protocol NCT01998841 (GN28352) from Week 130 to Week 224 and the second \[\^18F\]GTP1 tau PET scan from Week 248 to Week 260. The third and optional \[\^18F\]GTP1 tau PET scan will supplement the two primary scans.