Whereas all serum samples showed TGF-β1 concentrations above the LLOQ, these were generally low in the AH and ranged below the LLOQ in several samples, including the control group (4/17, 24%), non-apparent DR group (9/23, 39%), mild/moderate NPDR group (4/13, 31%), and advanced NPDR/PDR group (1/14, 7%). The gene discussed is TGFB1; the disease is non-proliferative diabetic retinopathy.