VGF and Alzheimer disease: VGF (non-acronymic) is a polypeptide induced in PC12 cells by neurotrophic factors.<h4>Objective</h4>This systematic review aimed to determine whether VGF and/or its derived peptides can be used as biomarkers for the diagnosis of ALS, PD, and AD with specific attention to (1) the levels of VGF and/or its derived peptides, (2) amyloid-beta, (3) dopamine, and (4) cognitive score.<h4>Methodology</h4>A search was undertaken in the Ovid EMBASE, Cochrane Library, PubMed, Scopus, and Web of Science for observational studies.