MAPT and Alzheimer disease: To date, validated biomarkers associated with AD include measurement of brain Aβ deposition presented by Aβ42 levels in cerebrospinal fluid (CSF), cortical amyloidosis on positron emission tomography (PET), measures of AD-typical neurodegeneration indicated by total-tau (t-tau) and phosphorylated-tau levels in CSF, hypometabolism on PET, and cerebral atrophy on magnetic resonance imaging (MRI)5.