(CCSP052) PHENOTYPIC DIFFERENCES BETWEEN "COMMON" LONG QT TYPE 1 VARIANT CARRIERS IN THE NATIONAL HIRO REGISTRY

Background: Long QT Syndrome (LQTS) type 1 (LQT1) is caused by pathogenic variants in the KCNQ1 gene. The majority of KCNQ1 variants are family-specific, but certain variants have been identified in multiple families, due to either founder effects or multiple origin events. Some KCNQ1 variants are associated with high or low risk of adverse cardiac events. This study aimed to identify distinguishing cardiac phenotypes and outcomes associated with the three most common KCNQ1 variants identified in the National HiRO-LQTS Registry.

METHODS AND RESULTS: This study included 294 LQT1 patients enrolled in the National HiRO Registry who are over age 18 and heterozygous for a pathogenic or likely pathogenic KCNQ1 variant. Participant demographic, clinical, and diagnostic data from those with the three most common KCNQ1 variants in the HiRO registry were compared to those with more rarely identified KCNQ1 variants. Data was stratified by sex, and statistical analysis was performed using R 4.1.1. Categorical variables were compared using Fisher's exact test and continuous variables compared using ANOVA (Table 1). Regression analysis was performed to control for sex and proband status.

Of the 294 adult LQT1 patients enrolled in the National HiRO-LQTS Registry, 72 (25%) were identified to have one of three common KCNQ1 variants: Leu266Pro (n=26; 9%) Val205Met (n=25; 9%) and Gly168Arg (n=21; 7%). Most participants were female (n=201; 68%) with an average age of 45 at last assessment. Female participants with the V205M and L266P variants were more likely to report cardiac symptoms (39% and 35% respectively), though not statistically significant (p=0.305), with 17% of the V205M female carriers (n=3) experiencing a cardiac arrest. There was no statistically significant difference in resting or 4-min recovery QTc measurements amongst different variant carriers, with sex identified to be a significant confounder on regression analysis for resting QTc and 4-min recovery QTc (p < 0.001 and p< 0.05, respectively). Further analysis of sex differences in QTc measurements using Tukey’s HSD test showed the effect was only significant between males and females within the Other KCNQ1 variants (p < 0.001). A higher proportion of those with the V205M variant were on non-selective beta-blockers (n=15; 60%) and had an ICD implanted (n=6; 24%) compared to other KCNQ1 variant carriers.

Conclusion: Elevated cardiac event rates were reported in female carriers with V205M and L266P variants, despite similar resting or 4-min recovery QTc measurements. Future research identifying phenotypic differences amongst those with specific KCNQ1 variants is needed to inform genotype-specific care.