In patients with longstanding T1D, cells with a low level of insulin co-express markers of β- (Nkx6.1, Pdx1, PC1/3, and GLUT1) and α- (glucagon, ARX, GLP-1, and GC) cells sharing a mixed β/α phenotype; some SS-, PP-, and ghrelin cells also express a low level of insulin [29]. This evidence concerns the gene GCG and type 1 diabetes mellitus.