Obese mice lacking appetite control due to a genetic deficiency related to the hormone leptin (whether in the receptor or the ligand), which therefore affects its role in the insulin–glucose axis, have been studied with regard to the underlying pathology in diabetic tissue [2], including the retina [4, 14], revealing some of the pathological features of human diabetic retinopathy. The gene discussed is INS; the disease is diabetic retinopathy.