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Figure 5 The predicted secondary structure of the cardiac sodium channel and locations of mutations causing the Brugada syndrome and chromosome 3–linked long QT syndrome. The channel consists of four putative transmembrane domains (DI–DIV), with each domain containing six transmembrane segments (S1–S6). The Brugada syndrome mutations are shown in circles with dark lettering and long QT syndrome–associated mutations are in circles with white lettering. Adapted with permission from Chen et al. (55).