NEFL and Parkinson disease: Its increase in both CSF and blood has been largely observed in various conditions: Alzheimer’s disease (AD); Parkinson’s disease (PD); typical Parkinsonism; frontotemporal dementia; multiple sclerosis and amyotrophic lateral sclerosis (ALS), Creutzfeldt–Jakob disease, etc. [34,44]; therefore, NF-L is a general marker of neurodegeneration, brain trauma and neuroinflammation.