Since the first clinical trials in patients with type 2 diabetes mellitus, treatment with SGLT2 inhibitors (SGLT2i) has produced an early and sustained increase in hemoglobin and hematocrit levels of 0.5–0.7 g/dL, a finding subsequently confirmed in clinical trials involving patients with heart failure (HF) and chronic kidney disease (CKD) [50–52]. The gene discussed is SLC5A2; the disease is heart failure.