Some investigations in affective disorders [21, 22], schizophrenia [23], substance use disorders (SUD) [24, 25], and anorexia nervosa (AN) [26], reported alterations of NfL levels in either CSF, blood, or both, and with magnitudes intermediate between physiological states and some neurological disorders with current disease activity (e.g., frontotemporal dementia [FTD], Parkinson’s disease [PD], or multiple sclerosis [MS] with radiological active status) [27]. This evidence concerns the gene NEFL and Parkinson disease.