MAPT and early-onset autosomal dominant Alzheimer disease: In Alzheimer disease (AD), there is a need for biomarkers that reflect the key pathophysiology of the disease: neurodegeneration and β-amyloid (Aβ) and tau protein pathology.1 Over the past 2 decades, significant efforts have been made to identify in vivo brain indicators and fluid-based biomarkers for preclinical and clinical AD.2, –, 4