NTN1 and Parkinson disease: Specifically, the median concentration of NTN‐1 in the PD group was 194.0 pg/mL (with a range of 105.4–558.6 pg/mL), while the HC group had a median of 325.7 pg/mL (with a range of 176.1–836.0 pg/mL) (p = 0.016, Mann–Whitney U test).