Synaptic vesicle glycoprotein 2 A (SV2A), located in the synaptic vesicles at presynaptic terminals, is regarded as the first in vivo marker of synaptic density [14], and numerous studies have used synaptic positron emission tomography (PET) tracers (e.g., [11C]UCB-J [15, 16] and [18F]UCB-H [17, 18]) to indicate the SV2A level in the hippocampal tissue of the participants to identify those with early AD and assess responses to disease-modifying therapy. Here, SV2A is linked to Alzheimer disease.