NEFL and amyotrophic lateral sclerosis: Given its sensitivity to axonal damage, NfL has emerged as a valuable marker of early neurodegeneration and progression of several neurological diseases, including AD, Parkinson’s disease (PD) and atypical parkinsonian syndromes (APS), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS) among others (52, 53).