In total, 3 SNPs exhibit significant association with 6MP-induced leukopenia (P < 0.01, Table 1), including two well-reported variants at NUDT15 (rs116855232, P = 6.37 × 10−11) and TPMT (rs1142345, P = 0.003), respectively. The gene discussed is TPMT; the disease is Decreased total leukocyte count.