GRM4 and Alzheimer disease: In line with this finding, in our study, some presynaptic proteins showed minimal changes in AD whereas others were decreased to a greater degree (> 30%), as exemplified by CPLX1, CPLX2, vesicular glutamate transporter 2 (SLC17A6), SYNGR1, RAB3B, NCS1, SYNGR3, GRM4, and RAB3A (Fig. 5).