Our results demonstrate that serum IGF-1 levels are significantly higher in a de novo, drug-naïve PD patient cohort, which bolsters the hypothesis that elevated serum IGF-1 levels may act as a biomarker for the early diagnosis of PD; however, well-designed clinical investigations evaluating sensitivity, specificity and predictive value in the diagnosis of PD must be done to further test this hypothesis. Here, IGF1 is linked to Parkinson disease.