MAPT and Alzheimer disease: Previous studies using CSF biomarker [14, 15] and PET imaging [16–18] have demonstrated that individuals who are Aβ positive and tau positive (A+/T+) are at higher risk of AD than those who are Aβ negative and tau negative (A-/T-), Aβ positive and tau negative (A+/T-), and Aβ negative and tau positive (A-/T+).