GCG and type 2 diabetes mellitus: KEGG enrichment analysis (Fig. 3E; Additional file 1: Table S7) indicated that neurons’ marker genes were participating in insulin secretion, glucagon signaling pathway, and maturity-onset diabetes in young adults; epithelial cells’ marker genes and smooth muscle cells’ marker genes were strongly coupled to the most common vascular outcome of T2DM, coronary heart disease (CHD) [8], especially the epithelial cells' marker genes, which were linked to multiple CHD-related pathways (hypertrophic and dilated cardiomyopathy, atherosclerosis, arrhythmogenic right ventricular cardiomyopathy).