It may be the case that one partial loss-of-function variant (e.g., T7I) and one total loss-of-function variant (e.g., D76N) can together cause JLNS, but that partial loss-of-function KCNE1 variants do not have a high penetrance for a prolonged QT interval when heterozygous with wildtype (Romano-Ward syndrome). This evidence concerns the gene KCNE1 and Romano-Ward syndrome.