INS and type 2 diabetes mellitus: Notably, although the general consensus is that both IR and β-cell dysfunction are essential components in the development of T2DM, recent genome-wide association studies (GWAS) have discovered that the great majority of genetic variants conferring risk for T2DM are associated with β-cell function, implicating that β-cell dysfunction rather than insulin sensitivity might be relatively more important in T2DM pathogenesis [2, 16, 17].