Final answer:
QT syndrome can result from mutations in sodium, potassium, or calcium channels, which disrupt the heart's electrical cycle and can lead to irregular heartbeats. Potassium channel blockers used in treatment illustrate the effect on the QT interval in the ECG.
Step-by-step explanation:
The channelopathy known as QT syndrome is a result of mutations in sodium, potassium, or calcium channels. These ion channels are critical for the proper electrical functioning of the heart. When these channels do not work properly due to mutations, they can disrupt the timing of the heart's electrical cycle, leading to the condition known as long QT syndrome. This can cause irregular heartbeats, which may be life-threatening. For instance, potassium channel blockers, like amiodarone and procainamide, demonstrate this by impeding the movement of K+ through voltage-gated K+ channels, affecting the repolarization phase of the cardiac action potential, which is represented in the ECG as the QT interval.
Since variations of the QT syndrome can be caused by mutations in different ion channels, the correct answer to the question is E) sodium, potassium, or calcium channels.