NEFL and neurodegenerative disease: NfL is a major structural protein only expressed in neurons and an indicator of axonal degeneration and injury used as a blood and CSF biomarker in the assessment of neurodegenerative diseases including frontotemporal lobal degeneration, amyotrophic lateral sclerosis, Alzheimer’s disease (AD), Multiple Sclerosis and primary tauopathies (15–17).