GCG and type 2 diabetes mellitus: Cells co-expressing β-cell markers (insulin, Nkx6.1, PDX1, PC1/3, GLUT1) together with α-cell markers (glucagon, ARX, GLP-1, GC), in various combinations, have been identified in individuals with both type 1 [21,22] and type 2 diabetes [23,24,25].