Since the study by Poyan-Mehr et al. revealed that the de novo NAD+ biosynthetic pathway is impaired in ischemic AKI, due to reduced expression and activity of QPRT [125] (Figure 1), the defective de novo pathway has been linked to AKI-to-CKD progression, a premature renal aging phenotype and staging of CKD in humans. The gene discussed is QPRT; the disease is chronic kidney disease.