KCNQ1 and familial long QT syndrome: Of the three pathogenic mutations in the present study, KCNQ1-R174C was previously reported to be associated with both heterozygous LQT114 and homozygous autosomal-recessive LQT115, in which the homozygous KCNQ1-R174C carrier displayed extreme QT prolongation and suffered multiple breakthrough cardiac events before succumbing to his malignant LQTS phenotype.