While NfL levels are not increased in either blood or CSF of parkinsonian patients, it is noteworthy that they rise in atypical forms of parkinsonian syndromes such as PSP, MSA, and CBD in both CSF (Bäckström et al., 2015; Herbert et al., 2015) and blood (Hansson et al., 2017; Lin et al., 2018; Marques et al., 2019; Ashton et al., 2021). This evidence concerns the gene NEFL and red-green color blindness.