Pharmacogenetic testing and drugs associated with severe ADRs were HLA-B*58:01-allopurinol induced SJS/TEN/drug reaction with eosinophilia and systemic symptoms (DRESS), HLA-B*57:01-abacavir induced hypersensitivity reaction, HLA-B*15:02 and HLA-A*31:01- carbamazepine induced SJS/TEN/hypersensitivity, TPMT-azathioprine induced severe bone marrow toxicity, UGT1A1- irinotecan induced severe neutropenia and DPYD- fluoropyrimidines induced severe hematologic/GI toxicity. The gene discussed is TPMT; the disease is Decreased total neutrophil count.