Contribution of a KCNH2 variant in genotyped long QT syndrome: Romano-Ward syndrome under double mutations and acquired long QT syndrome under heterozygote

KCNH2 p.His492Tyr variant presented Romano-Ward syndrome in the presence of another mutation and heterozygous carriers had mild phenotypes while even heterozygous carriers should be cared for not to encounter secondary factors because incidental factors could manifest “latent” form of p.His492Tyr heterozygous carriers.