Based on an ROC curve analysis, the identification of PD patients with serum IGF-1 levels had an area under the curve (AUC) value of 0.895, sensitivity of 87%, specificity of 80%, and cutoff value of 123.8 mmol/L, and the identification of PD patients with serum EGF levels had an area under the curve (AUC) value of 0.758, sensitivity of 77%, specificity of 63%, and cutoff value of 59.45 pg/mL. Here, EGF is linked to Parkinson disease.