INS and type 2 diabetes mellitus: Based on current data, epigenetics could explain the apparent missing heritability of T2D, with epigenetic alterations in genes implicated in insulin secretion (GIPR, SLC30A8, PTPRN2), glucose homeostasis and lipid metabolism (TXNIP, CPT1A, SREBF1, ABCG1), and energy balance (FTO, PPARGC1A) in blood, as well as in insulin-responsive tissues.