Our multivariate analysis shows that female gender and age (older than 9 years) are suggestive as protective factors for the development of leukopenia, even with the polymorphisms in NQO1 609C>T or GSTM1. However, when we evaluate NQO1 609C>T and GSTM1 gene polymorphisms, the occurrence of leukopenia is favored (model 3, Table 5). The gene discussed is NQO1; the disease is Decreased total leukocyte count.