Comparison of HO-1 levels between young and elderly individuals in the early PD, advanced PD, and normal control groups also showed no significant differences [early PD: 2.42 ± 0.62 vs. 2.34 ± 0.70 ng/ml, p = 0.75; advanced PD: 2.19 ± 0.60 vs. 2.23 ± 0.56 ng/ml, p = 0.84; normal controls: 2.16 (1.73, 2.39) vs. 2.09 (1.68, 2.33) ng/ml, p = 0.69; Supplementary Figures 1F–H]. Here, HMOX1 is linked to Parkinson disease.