EXT1 and Alzheimer disease: Ubiquitously expressed on cell surfaces, HSPGs consist of a core proteoglycan with heparan sulfate chains, the elongation of which is facilitated by the glycosyltransferase activity of Exostosin-1 (EXT1) in the brain 26 Among the diverse family of HSPGs, neuronal SDC3 is particularly relevant to AD pathophysiology, promoting the propagation of amyloid pathology and the neuronal uptake of tau27,28.