NEFL and Parkinson disease: PD patients had lower CSF Aβ1-42 (β = − 106.9, SE 39.9, p = 0.008), α-syn (β = − 183.1, SE 65.0, p = 0.005), t-tau (β = − 24.3, SE 5.7, p < 0.001) and p-tau levels (β = − 2.7, SE 0.6, p < 0.001) than those of the controls, while the serum NfL levels did not exhibit a significant difference.