Although the TMP-SMX has been regarded as a first-line regimen for prophylaxis of PCP, it often has to be switched to second-line treatment such as dapsone, atovaquone, and atomized pentamidine due to TMP-SMX associated AEs and drug intolerance caused by neutropenia and glucose-6-phosphate dehydrogenase (G6PD) deficiency [9,10,36]. The gene discussed is G6PD; the disease is Decreased total neutrophil count.