P2RX7 and extrapulmonary tuberculosis: Evidence for P2X7 receptor involvement in mycobacterial killing comes from studies showing that loss-of-function polymorphisms in the human P2X7 receptor gene lead to increased susceptibility to M. tuberculosis. Fernando et al. [36] investigated the prevalence of the 1513 A>C polymorphism in two independent Southeast Asian cohorts, and found a strong association with the 1513 A>C polymorphism and extrapulmonary tuberculosis.