In the 70 families we found 64 different mutations; 22 in KCNQ1, 28 in KCNH2, 9 in SCN5A, 3 in KCNE1 and 2 in KCNE2. All patients were heterozygous carriers of a single mutation, except one double heterozygous proband (1.4% of families), who carried p.R583G in KCNQ1 and p.A93T in KCNE1. Twenty-six of the mutations have only been described in Danish LQTS patients (Tables 1, 2, 3), 18 have not been reported previously. This evidence concerns the gene SCN5A and familial long QT syndrome.