More importantly, the delivery of exogenous growth factors contained in PRP, such as EGF, IGF, and TGF-β, has been shown to have neurotrophic effects in CNS injuries and neurodegenerative diseases (Flanders et al., 1998; Wang et al., 2000; Kojima and Tator, 2002). This evidence concerns the gene IGF1 and neurodegenerative disease.