The absence of tuberculosis events could be due to chance, but it could also be due to the stringent requirements intended to minimise the risk of tuberculosis, including enrolment requirements for stable ART for at least 3 months, previous completion of tuberculosis preventive therapy, favourable HIV viral load and CD4 cell counts, exclusion of past tuberculosis, and a negative sputum for tuberculosis at baseline. The gene discussed is CD4; the disease is tuberculosis.