NEFL and Alzheimer disease: Specifically, in the case of AD levels of NfL [186,191,192], NfL during the progression of PD [193,194], and in the case of ALS, NfL and phosphorylated neurofilament heavy chain (pNFH) [190,195,196] reflect global neuronal axonal injury and, therefore, act as a prognostic biomarker for diagnosis of AD, PD, and ALS (Figure 3).