NEFL and Parkinson disease: Indeed, CSF NfL levels correlate with brain atrophy (Dhiman et al., 2020; Pereira et al., 2017) and are elevated across dementias, MCI (Olsson et al., 2016; Petzold et al., 2007; Rosengren et al., 1999; Zetterberg et al., 2016) and neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD) (Gaetani et al., 2019).