Clinical studies have shown that Caucasians with UGT1A1*28 gene mutants (TA6/7 and TA7/7) have a higher risk of severe granulocytopenia and diarrhea than those with wild-type UGT1A1*28 (TA6 /6) after receiving irinotecan [21]. The gene discussed is UGT1A1; the disease is Decreased total granulocyte count.