EGF and Parkinson disease: IGF-1 and EGF levels in the early stage and middle-late stage PD groups were higher than those in the healthy control group, and the differences between the three groups were statistically significant (IGF-1: 2 = 94.89, df = 2, P < 0.001; EGF: 2 = 32.60, df = 2, P < 0.001) (Fig. 1A, B).