MAPT and Alzheimer disease: However, we believe it is more likely that most current AD drugs are flawed in that (1) they have minimal or no bioavailability within the brain’s neurons [4], and (2) they do not target the primary culprits of AD, which recent studies indicate are small toxic “oligomers” of β-amyloid (Aβ) and tau [5,6,7,8,9,10,11,12].