Figure 1B showed that the DGUOK protein expression was completely abrogated after infection of cells with DGUOK-KO lentivirus. To identify the level of NAD+, we first examined NAD+ LC-MS curve (Figure 1B). LC-MS analysis revealed a significant decrease in the NAD+ level in H1650 DGUOK-KO cells (Figures 1C–E). These results indicate a critical role of DGUOK in regulation of NAD+ biogenesis. The gene discussed is DGUOK; the disease is infection.