MAPT and Alzheimer disease: More specifically, in AD, cognitive impairment is highly correlated with synaptic loss in the association cortex and limbic system.7,8 Synaptic disruption is thought to be associated with toxic β-amyloid or tau oligomers and is already observed in the earliest clinical stages of AD.9 These findings suggest that the ability to assess synaptic density in vivo could improve clinical research in AD and potentially could serve as a valuable surrogate marker for disease severity in clinical trials.