NFL serum concentration has also been associated with the severity of symptoms of different NDs, e.g., it positively correlates with the Unified Parkinson’s Disease Rating Scale (UPDRS) in PD, motor and cognitive impairment in HD, Alzheimer’s Disease Assessment Scale-cognitive subscale (ADAS-cog) in AD and negatively with Mini-Mental State Examination (MMSE) in AD [11]. This evidence concerns the gene NEFL and Huntington disease.