We screened for mutations in KCNQ1 and KCNH2 in 3 groups: 10 cases of sudden death involving MP use (male/female ratio: 10:0; mean age: 51.60 years), 10 cases involving NPS use (male/female ratio: 9:1; mean age: 32.90 years), and a control group comprising 100 Japanese individuals without LQTS. This evidence concerns the gene KCNQ1 and familial long QT syndrome.