To date, the diagnostic performance of a protein based IP-10 test for M. tuberculosis infection has been evaluated in more than 40 clinical studies; showing comparable sensitivity to IFN-γ for tuberculosis cases; comparable specificity in unexposed controls; stronger association between test positivity and exposure in persons at risk of tuberculosis; better test sensitivity in HIV-infected patients with low CD4 T cell count; and more robustness in children <5 years of age [12]. The gene discussed is CD4; the disease is tuberculosis.