MAPT and Alzheimer disease: Biomarkers are available to aid in the diagnosis of AD, and several studies have shown that β-amyloid1-42 (Aβ1-42) level is decreased and that the total tau (t-tau) and phosphorylated tau (p-tau) levels are increased in the cerebrospinal fluid (CSF) of patients with AD compared with cognitively healthy controls [8-11].