The LQT2 subtype is the second-most common form of Romano–Ward syndrome, responsible for 25 to 30% of all cases. It is caused by variants in the KCNH2 gene (also known as hERG) on chromosome 7 which encodes the potassium channel that carries the rapid inward rectifier current IKr. This current contributes to the terminal repolarisation phase of the cardiac action potential, and therefore the length of the QT interval.
