Additional Table 1.

Comparison of serum GDNF level in three groups based on k-means clustering

	Mean ± SD	Median (IQR)	Test of normality (Kolmogorov-Smirnov)	Statistics (Kruskal-Wallis H)	P-value
Healthy control	559.36 ± 234.33	533.59 (431.19, 612.82)	0.016	39.895	0.000
PD-high-GDNF	395.50 ± 78.77	384.65 (338.98, 430.77)	0.200
PD-low-GDNF	175.86 ± 69.12	139.76 (130.25, 205.91)	0.012

Plasma GDNF was detected by ELISA. GDNF: Glial cell derived neurotrophic factor; IQR: inter-quartile range; PD: Parkinson’s disease.