In our study, the risk of severe recurrent neutropenia (grades 3 and 4) was independently influenced by the ABCB1 rs17064 genotype AT (OR 5.13; 1.38–19.02; p = 0.014), UGT2B4 rs1131878 genotype AG (OR 3.78; 1.26–11.24; p = 0.016), and ALDH5A1 genotype AC (OR 3.94; 1.34–11.53; p = 0.012) (Table 3). The gene discussed is UGT2B4; the disease is neutropenia.