The variants in Cy activation genes CYP2A6*2 (rs1801272), CYP2B6*5 (rs3211371), CYP2C8 (rs10509681 and rs11572080, called CYP2C8*3 haplotype) and CYP2C9 (rs1799853) were associated with a higher incidence of grade II-IV GVHD and grade III-IV aGVHD (Table 3). The gene discussed is CYP2C9; the disease is graft versus host disease.