In an out-of-target glycemic-control group of adult subjects with T1D, during this 28-week, multicenter, prospective, interventional, single-arm, open label phase 4 study, the switching from BID basal insulin to OD Gla-300 resulted in improved morning (pre- and post-breakfasting), late-afternoon (pre-dinner) and evening (pre- and post-dinner) capillary blood glucose levels. This evidence concerns the gene INS and type 1 diabetes mellitus.