EDN1 and diabetes mellitus: To (i) investigate expression of the endothelin-1 (ET-1) gene in peripheral blood mononuclear cells (PBMCs) of patients with type 2 diabetes mellitus (DM) and (ii) determine what correlations, if any, exist between expression of ET-1 in patients with type 2 DM and treatment, clinical features, and biochemical markers in diabetic retinopathy (DR).