NEFL and Parkinson disease: Associations between psychiatric symptoms and NfL levels have been also reported in a number of neurological (e.g., MS, PD, AD, stroke) [96–98, 136], inherited (e.g. Wilson’s disease and Down Syndrome) [137–140], and systemic (e.g., COVID-19, systemic lupus erythematosus, HIV) [141–146] conditions.