VGF and obesity due to melanocortin 4 receptor deficiency: While CSF biomarkers including VGF have utility in the diagnosis of AD, comparison of serum or plasma VGF levels in AD and control subjects has less diagnostic specificity, as plasma VGF levels are reduced in Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and MDD, and are regulated by obesity and type 2 diabetes (Supplementary Table 3).