S100A4 and proliferative diabetic retinopathy: Patients with proliferative and non-proliferative diabetic retinopathy are characterized by the abundance of S100A family proteins (S100A4, A100A6, S100A8, S100A11), but the most promising protein is S100A13 [31], which is the only S100A protein that has not been observed in our study as mentioned above (Supplementary Materials and Table 1).