Table 2 shows a comparison of genotype and allele frequencies between patients who developed grade 4 neutropenia versus treatment tolerant patients. Patients carrying the XDH rs2281547 CC/TC genotype had a significantly higher incidence of grade 4 neutropenia (p = 0.01) as compared to TT genotype. Similar results were found for the allele analysis. The incidence of grade 4 neutropenia was higher in patients carrying XDH rs2281547 C allele (38.6%% vs. 22.3%, p = 0.003). The gene discussed is XDH; the disease is neutropenia.