When the levels of HO-1 were compared among the early PD, advanced PD and control groups in young and elderly subjects, the results showed no statistically significant differences [young subjects: 2.43 (1.99, 2.97) vs. 2.19 (1.62, 2.61) vs. 2.16 (1.73, 2.39) ng/ml, p = 0.15; elder subjects: 2.34 ± 0.70 vs. 2.23 ± 0.56 vs. 2.02 ± 0.49 ng/ml, p = 0.22; Supplementary Figure 1E]. This evidence concerns the gene HMOX1 and Parkinson disease.