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). This evidence concerns the gene NEFL and amyotrophic lateral sclerosis.