Predictive genomic markers for severe adverse drug reactions

Severe adverse drug reactions are an important issue to be considered during proper drug usage in postmarketing period. Most severe adverse reactions are idiosyncratic and unrelated to their pharmacological actions via primary targets. Although these reactions were not predictable, recent developments in the field of genomics have revealed closely associated markers responsible for some severe adverse reactions, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). This review demonstrates genomic biomarkers for SJS/TEN and drug-induced liver injury (DILI) that were found mainly in Japanese patients and reveal ethnic differences. We and other groups have found the following associations of SJS/TEN with susceptible drugs: 1) HLA-B*58:01 for allopurinol-related cases; 2) HLA-B* 15:11 and HLA-A*31:01 for carbamazepine-related cases; 3) HLA-B*51:01 for phenobarbital-related cases; 4) HLA-A* 02:07 for zonisamide-related cases; 5) CYP2C9*3 for phenytoin-related cases; and 6) HLA-A*02:06 for cold medicinerelated cases. The allele frequencies of these related HLA types vary among Asian populations. In addition, direct (noncovalent) binding of carbamazepine or an allopurinol metabolite, oxypurinol, to the associated HLA-type proteins was suggested. Associated genomic biomarkers are also summarized for DILI in Japanese and Caucasian populations. The application of these genomic biomarkers to prevent the onset of a reaction has been utilized in a few countries. However, in Japan, the package inserts only contain precautions that cite the research findings. To overcome this limitation, the following points should be addressed: 1) factors responsible for the development of SJS/TEN should be identified in addition to the above-mentioned HLA alleles; and 2) an inexpensive genotyping strategy and assay methods should be developed to provide a pharmacoeconomical viewpoint. Further research on severe adverse reactions is warranted.