The melatonin receptor 1B (MTNR1B) gene is a well-established T2D locus with significant associations with multiple glucose-related traits including FG (21, 23, 28–30, 67, 94–101), glycated hemoglobin (31–33, 102, 103), insulin levels, insulin disposition index and insulin secretion rates (104, 105), acute insulin response, HOMA-B (21), and T2D (27, 34, 35, 37–40, 42, 43, 106, 107). Here, MTNR1B is linked to type 2 diabetes mellitus.