MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer's disease biomarkers are divided into two types: early biomarkers, which measure amyloid accumulation in the brain (e.g., PET imaging, CSF amyloid), and late biomarkers, which measure neurodegeneration [e.g., structural MRI, fluorodeoxyglucose-positron emission tomography (FDG PET), CSF tau].