PROS1 and Alzheimer disease: Secretion of Aβ monomers is central to AD pathology, and the impact of Aβ on NCAM, PSA-NCAM, and sialyltransferase enzymes is not fully understood, yet these molecules play critical roles in neural plasticity, cell signaling, and cognitive functions (Schaeffer et al., 2011; Rendeiro et al., 2014; Varbanov and Dityatev, 2017).