NEFL and amyotrophic lateral sclerosis: The intuition that purely neuronal proteins such as NFs might be elevated in extracellular fluids in neurodegenerative diseases as a result of the release from apoptotic cells or as part of the cell remodelling process dates back 1996 when Rosengren originally reported that CSF NfL levels are increased in patients with ALS and other neurological diseases [45].