Compared to the baseline measurements, there was a notable reduction in the L-arg pool within red blood cells, as indicated by a significant decrease (3.52 ± 0.2 vs. 3.10 ± 0.2 μmol/g Hb, p = 0.022, paired t-test) shown in Figure 2A. In contrast, the L-arg levels in plasma (Figure 2B) remained stable in patients with diabetes over five years of disease progression (0.28 ± 0.04 vs. 0.24 ± 0.03 μmol/g protein, p = ns, respectively). The gene discussed is GSTM1; the disease is diabetes mellitus.