PCDHGC5 and Alzheimer disease: Importantly, our analysis also identified several lesser-known or novel proteins with decreased abundance, including SHISA7 (inhibitory synaptic regulation), SORCS3 (intracellular trafficking of APP), CNR1 (neurotransmitter release), JAG1 (notch signaling) (51), and PCDHGC5 (cell adhesion), which, though not canonical AD biomarkers, are functionally linked to synaptic regulation, vesicle trafficking, neurotransmission, and signaling.