In this study, a toddler LQTS proband was found to have SNV c.1264A > G in the KCNQ1 gene, resulting in p.Lys422Glu (K422E) amino acid substitution at the cytoplasmic C-terminus tail of the alpha-subunit of the IKs channel. Here, KCNQ1 is linked to familial long QT syndrome.