SYP and Alzheimer disease: The expression levels of six genes encoding synaptic proteins, such as SYP, synaptotagmin-1 (SYT1), VGLUT1, postsynaptic density protein 95 (PSD95), serotonin 2A receptor (5HTR2A) and N-methyl-D-aspartate receptor (NMDAR) (all previously described to be involved in AD-related synaptic dysfunction [14, 51–53]) were analyzed using RT–qPCR and showed significant upregulation of PSD95 (p = 0.044) and a tendency toward 5HTR2A upregulation (p = 0.06) in the AD group (Fig. 8C).