Given the reports of elevated NfL levels in CSF or plasma in genetic, inflammatory, and other neurodegenerative diseases [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40], NfL in body fluids appears to be a general, not disease-specific, but sensitive marker of neurodegeneration due to the loss of neurons and axons. This evidence concerns the gene NEFL and neurodegenerative disease.