NEFL and Parkinson disease: After 2 years of follow‐up, the PD group exhibited significantly increased levels of the CSF biomarkers tau (t62 = −2.570, P = .013), P‐tau (t46 = −2.458, P = .018), α‐syn (t58 = −2.350, P = .022), NFL (z = −3.769, P < .001), and YKL‐40 (t62 = −3.682, P < .001) when compared with baseline levels (Figure 1 and Supplementary Figure S1).