Biophysical properties of mutant KCNQ1 S277L channels linked to hereditary long QT syndrome with phenotypic variability

► The KCNQ1 S277L mutation causes long QT syndrome 1. ► S277L subunits are non-functional. ► S277L suppresses wild type IKs in dominant-negative fashion. ► Modifying factors determine the individual clinical phenotype.