Guicheney, Pascale

KCNQ1 encodes the voltage-gated α-subunit of the I Ks channel complex (Kv7.1), and KCNQ1 mutations are associated with multiple arrhythmia syndromes. Over the past 12 years, hundreds of different KCNQ1 mutations have been linked to congenital long QT syndrome but only three KCNQ1 variants, each identified in only one family, are linked to familial early-onset AF (<50 years of age). The scant genetic linkage between KCNQ1 and early-onset AF raises the question as to whether these KCNQ1 variants actually cause familial early-onset AF or simply unmask a latent genetic predisposition. We now report that a single KCNQ1 variant, pArg231His or R231H, is identified in five unrelated families with a high penetrance of familial early-onset AF. Whole-cell patch clamp of cells heterologously expressing the obligatory I Ks β-subunit KCNE1 with wild-type KCNQ1 (WT) or WT and R231H (to mimic the patients’ genotypes) showed that cells co-expressing R231H increased current at negative and resting membrane potentials. Additionally, currents recorded from cells using a human atrial action potential (AP) waveform at physiological temperature showed that WT is minimally activated during the atrial AP and co-expression of R231H increases current measured during the atrial AP waveform by greater than 20-fold (WT, n = 10; WT & R231H, n = 12, p<0.0001). Simulations using a computational model of a human atrial AP also predicted that I Ks is normally minimally activated in the atria and R231H would dramatically increase I Ks and shorten the atrial AP. We conclude that KCNQ1 mutations are capable of causing familial early-onset AF by increasing I Ks during the atrial AP and shortening atrial refractoriness.

Background: Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility. Methods: We conducted genome-wide association studies followed by transethnic meta-analysis in 1656 unrelated patients with LQTS of European or Japanese ancestry and 9890 controls to identify susceptibility single nucleotide polymorphisms. We estimated the common variant heritability of LQTS and tested the genetic correlation between LQTS susceptibility and other cardiac traits. Furthermore, we tested the aggregate effect of the 68 single nucleotide polymorphisms previously associated with the QT-interval in the general population using a polygenic risk score. Results: Genome-wide association analysis identified 3 loci associated with LQTS at genome-wide statistical significance ( P <5×10 −8 ) near NOS1AP , KCNQ1 , and KLF12 , and 1 missense variant in KCNE1 (p.Asp85Asn) at the suggestive threshold ( P <10 −6 ). Heritability analyses showed that ≈15% of variance in overall LQTS susceptibility was attributable to common genetic variation ( h2SNP 0.148; standard error 0.019). LQTS susceptibility showed a strong genome-wide genetic correlation with the QT-interval in the general population (r g =0.40; P =3.2×10 −3 ). The polygenic risk score comprising common variants previously associated with the QT-interval in the general population was greater in LQTS cases compared with controls ( P <10−13), and it is notable that, among patients with LQTS, this polygenic risk score was greater in patients who were genotype negative compared with those who were genotype positive ( P <0.005). Conclusions: This work establishes an important role for common genetic variation in susceptibility to LQTS. We demonstrate overlap between genetic control of the QT-interval in the general population and genetic factors contributing to LQTS susceptibility. Using polygenic risk score analyses aggregating common genetic variants that modulate the QT-interval in the general population, we provide evidence for a polygenic architecture in genotype negative LQTS.

R231H Causes a High Penetrance for Familial AFBackgroundAtrial fibrillation (AF) is the most common cardiac arrhythmia, and its incidence is expected to grow. A genetic predisposition for AF has long been recognized, but its manifestation in these patients likely involves a combination of rare and common genetic variants. Identifying genetic variants that associate with a high penetrance for AF would represent a significant breakthrough for understanding the mechanisms that associate with disease.Method and ResultsCandidate gene sequencing in 5 unrelated families with familial AF identified the KCNQ1 missense mutation p.Arg231His (R231H). In addition to AF, several of the family members have abnormal QTc intervals, syncope or experienced sudden cardiac arrest or death. KCNQ1 encodes the voltage‐gated K+ channel that conducts the slowly activating delayed rectifier K+ current in the heart. Functional and computational analyses suggested that R231H increases KCNQ1 current (IKCNQ1) to shorten the atrial action potential (AP) duration. R231H is predicted to minimally affect ventricular excitability, but it prevented the increase in IKCNQ1 following PKA activation. The unique properties of R231H appeared to be caused by a loss in voltage‐dependent gating.ConclusionsThe R231H variant causes a high penetrance for interfamilial early‐onset AF. Our study indicates R231H likely shortens atrial refractoriness to promote a substrate for reentry. Additionally, R231H might cause abnormal ventricular repolarization by disrupting PKA activation of IKCNQ1. We conclude genetic variants, which increase IKs during the atrial AP, decrease the atrial AP duration, and/or shorten atrial refractoriness, present a high risk for interfamilial AF.