GDNF and diabetes mellitus: Partial correlation analysis revealed a cluster of seven proteins (hepatocyte growth factor (HGF), macrophage colony-stimulating factor 1 (CSF-1), osteoprotegerin (OPG), IL-18R1, vascular endothelial growth factor A (VEGFA), glial cell line-derived neurotrophic factor (GDNF), and IL6) that were highly intercorrelated (Fig. 2C) and all positively associated with diabetes (Fig. 2A).