MAPT and Alzheimer disease: Diagnosis and staging per the latest NIA–AA clinical criteria: among the core biomarkers A (Aβ abnormality: decreased CSF Aβ42/40 ratio or amyloid PET positivity) and T (elevated p‐tau or tau PET positivity), abnormality in either core biomarker is sufficient to diagnose AD; disease severity is classified as mild–moderate–severe based on the degree of A/T abnormality