The distinction between type 1 and 2 developed gradually over the next five decades along with the realisation that insulin levels may be normal or raised in type 2 diabetes (T2D) and that a substantial population of β-cells survives lifelong (Butler et al., 2003; Clark et al., 1990; Porte & Kahn, 2001). Here, INS is linked to type 2 diabetes mellitus.