Response by Crotti et al to Letter Regarding Article, "Genetic Modifiers for the Long-QT Syndrome: How Important Is the Role of Variants in the 3' Untranslated Region of KCNQ1?"

We welcome the opportunity to respond to the expected comments by Amin et al regarding our article on the modifying role of 3′ untranslated region (3′UTR) single-nucleotide polymorphisms (SNPs) in type 1 long-QT syndrome patients.1 In the original cohort studied by Amin et al,2 the analysis of 3 small families supported the modifying role of 3′UTR SNPs. Amin et al now propose, as a possible reason for the different results, the predominance of haploinsufficient type 1 long-QT syndrome–causative mutations in our population. However, in our 3 founder families, 2 ( KCNQ1 A341V and also KCNQ1 IVS7-2A>G) of the 3 mutations have a dominant-negative effect,3,4 and only 1 ( KCNQ1 -G589D) reduces the ability of the mutated proteins to form functional tetramers leading to haploinsufficiency.5 This is exactly the same pattern of their 3 families: 2 have a dominant-negative effect …