Previous analyses (Williams & Dye, 2003; Williams et al., 2010) have found an exponential relationship between CD4 decrement in PLHIV not on ART and TB disease incidence, and their analysis has been widely used since in modeling analyses of the impact of HIV interventions on TB, linked HIV/TB resource planning (e.g., the OneHealth Tool frequently used to support applications to the Global Fund), and is used in TB burden estimation (Pretorius et al., 2014a; Pretorius et al., 2014b; Williams & Dye, 2003; Williams et al., 2010). The gene discussed is CD4; the disease is tuberculosis.