Paramyotonia congenita with an SCN4A mutation affecting cardiac repolarization.

Paramyotonia congenita (PC) is linked to mutations of the skeletal muscle voltage-gated sodium channel alpha-subunit gene SCN4A. The authors report a family where the proband and three of her four children have PC (mutation R1448C) and present repolarization abnormalities at electrocardiogram. They demonstrate that the SCN4A alpha-subunit gene is expressed in normal human heart. Cardiac consequences of mutations of the SCN4A gene may be insignificant in standard conditions, but critical if patients with PC are treated with drugs inducing QT prolongation.