NEFL and neurodegenerative disease: In this context, blood-based biomarkers of the ATX(N) system associated with cognitive deficits in neurodegenerative diseases, such as neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), amyloid beta (Aβ), and tau proteins, may help to understand the biological basis of cognitive dysfunction in SMIs and support differential diagnosis.