NEFL and Parkinson disease: Blood NfL correlated with CSF NfL also when adjusting for the confounding effects of age and sex (the whole cohort, β = 0.697, p < 0.001; controls, β = 0.344, p = 0.033; PD, β = 0.481, p < 0.001; APD, β = 0.523, p < 0.001).