Serum levels of IGF-1 were higher in Parkinson’s patients than in the normal group, with early-stage patients showing higher levels than those in mid-to late-stage disease, according to enzyme-linked immunosorbent assays conducted on serum IGF-1 levels in 100 healthy controls and 100 PD patients (including 49 early-stage and 51 mid- to late-stage cases). The gene discussed is IGF1; the disease is Parkinson disease.