[3] Moreover, PGx testing can help avoid adverse drug reactions, such as severe cutaneous adverse reactions (SCAR) due to allele mutations in HLA-B*58:01 during allopurinol treatment [4], as well as the Stevens–Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) induced by carbamazepine due to HLA-B*15:02 mutations [5]. The gene discussed is HLA-B; the disease is toxic epidermal necrolysis.