Table 1

 Characteristics of the three commonest genetic forms of long QT syndrome3,9

Long QT typeChromosomeGenePercentage of genotyped families affectedIon channelTypical trigger for syncope/sudden deathPercentage of cardiac events occurring during rest/sleep
111KCNQ1 (KVLQT1)42%Potassium (Iks), loss of functionExercise (especially swimming)3%
27KCNH2 (HERG)45%Potassium (Ikr), loss of functionEmotion/loud noise (especially waking from sleep)29%
33SCN5A7%Sodium (INa), gain of functionRest/sleep39%