PTN and Alzheimer disease: Compared to the control brains, GAGs isolated from the AD brains showed decreased binding to growth factors, such as fibroblast growth factor 2 (FGF-2), brain-derived neurotrophic factor and vascular endothelial growth factor (VEGF), and increased binding to tau, heparin-binding EGF-like growth factor and pleiotrophin [92], reflecting GAG structural alteration in AD brain.