KCNH2 and Familial short QT syndrome: Whilst there is ample precedent for in vitro investigations of heterozygous hERG mutations in SQTS using homozygous expression conditions [8, 14, 15, 16, 17, 18, 19, 20, 46], heterozygous subunit composition may lead to quantitative difference in the effects of the mutation to those reported here and previously [12] using homozygous expression.