VGF and major depressive disorder: VGF-derived peptides have been reported in several CSF proteomic studies to be potential biomarkers of neuropsychiatric and neurodegenerative disorders, including MDD and AD (Bartolomucci et al., 2010; Llano et al., 2019; van Steenoven et al., 2020; Quinn et al., 2021), consistent with possible functional roles for VGF in disease pathophysiology.