MAPT and Alzheimer disease: The majority of these studies are cross‐sectional and conducted on individuals with clinically diagnosed AD dementia, whereas others have only investigated MCI,170, 182, 198 both AD and MCI,111, 171, 172, 173, 174, 175, 176, 177, 178, 179, 185, 187, 191, 192, 193, 199, 201, 203, 204 Aβ or hyperphosphorylated tau positive,120, 131, 181, 182, 186, 190, 195, 196, 197, 200, 205APOE ε4 gene carriers,126, 145, 182, 198 and cognitively impaired189 individuals as their subjects.