BACKGROUND- Homozygous or compound heterozygous mutations in KCNQ1 cause Jervell 
and Lange-Nielsen syndrome, a rare, autosomal-recessive form of long-QT syndrome 
characterized by deafness, marked QT prolongation, and a high risk of sudden 
death. However, it is not understood why some individuals with mutations on both 
KCNQ1 alleles present without deafness. In this study, we sought to determine 
the prevalence and genetic determinants of this phenomenon in a large referral 
population of patients with long-QT syndrome. METHODS AND RESULTS- A 
retrospective analysis of all patients with long-QT syndrome evaluated from July 
1998 to April 2012 was used to identify those with ≥1 KCNQ1 mutation. Of the 249 
KCNQ1-positive patients identified, 15 (6.0%) harbored a rare putative 
pathogenic mutation on both KCNQ1 alleles. Surprisingly, 11 of these patients 
(73%) presented without the sensorineural deafness associated with Jervell and 
Lange-Nielsen syndrome. The degree of QT-interval prolongation and the number of 
breakthrough cardiac events were similar between patients with and without 
deafness. Interestingly, truncating mutations were more prevalent in patients 
with Jervell and Lange-Nielsen syndrome (79%) than in nondeaf patients (36%; 
P<0.001) derived from this study and those in the literature. CONCLUSIONS- In 
this study, we provide evidence that the recessive inheritance of a severe 
long-QT syndrome type 1 phenotype in the absence of an auditory phenotype may 
represent a more common pattern of long-QT syndrome inheritance than previously 
anticipated and that these cases should be treated as a higher-risk long-QT 
syndrome subset similar to their Jervell and Lange-Nielsen syndrome 
counterparts. Furthermore, mutation type may serve as a genetic determinant of 
deafness, but not cardiac expressivity, in individuals harboring ≥1 KCNQ1 
mutation on each allele.