NEFL and Parkinson disease: NFL levels have been linked to several neurodegenerative diseases, such as Alzheimer’s disease (AD)1, Parkinson’s disease (PD), atypical parkinsonian disorders (APD)2, frontotemporal dementia (FTD)3, amyotrophic lateral sclerosis (ALS)4, Huntington disease (HD)5,6, and multiple sclerosis (MS)7.