GFAP and neurodegenerative disease: In contrast, plasma neurofilament light (NfL) acts as a general marker of neuro-axonal degeneration, which occurs across several neurodegenerative diseases [17], whereas plasma glial fibrillary acidic protein (GFAP) is elevated early in the course of AD, showing an association with Aβ pathology [18] but also increased on other neurogenerative disorders.