We found a negative correlation between serum IGF-1 levels and UPDRS III scores in PD patients (r =  − 0.370, P < 0.001) and a negative correlation between serum EGF levels and UPDRS III scores in PD patients (r =  − 0.296, P = 0.003) (Fig. 3). The gene discussed is EGF; the disease is Parkinson disease.