One mutation, R367H, lies in the first P segment of the pore-lining region between the DIS5 and DIS6 transmembrane segments of SCN5A. A second mutation, A735V, lies in the first transmembrane segment of domain II (DIIS1) close to the first extracellular loop between DIIS1 and DIIS2, whereas the third mutation, R1192Q, lies in domain III.