Loss-of-function variants in founder population highlight atrial myopathy as susceptibility to atrial fibrillation

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and it's associated with genes responsible for cardiac conduction, cardiogenesis, and cardiac structure. The Finnish population has evolved in relative isolation and undergone several bottlenecks, resulting in enrichment of deleterious variants. This facilitates identification of possible causal genes through protein-truncating variants that likely would not have been identified in other populations.

Purpose

To identify novel genetic associations with large effect on AF risk.

Methods

We accessed publicly available summary statistics on AF (ICD-10 code I48) from the FinnGen project R6, containing 28,670 AF cases and 135,821 controls. Then, we annotated all variants in the summary statistics and extracted variants that were predicted with a high effect impact (n=7,113). To account for multiple testing, a false discovery rate cutoff <10% was applied. The UK Biobank was assessed for comparison of allele frequencies. Afterwards, we investigated protein and single-cell RNA expression of the genes of interest in human atrial tissue. Human atrial tissue was obtained by us from 7 individuals and used for mass spectrometry-based proteomics, while single-nucleus RNA sequencing (snRNAseq) data from human hearts was acquired by Tucker [1].

Results

In a genome-wide association study (GWAS) focusing on loss-of function (LOF) variation, we report two LOF variants in the structural genes SYNPO2L and CTNNA3 with much higher allele frequencies compared to non-Finnish Europeans (85-fold and 80-fold enrichment, respectively). The variants increase the risk of AF considerably, which is emphasized as the two variants show the highest effect sizes of all GWAS variants ever associated with AF (SYNPO2L; odds ratio [OR] = 2.79, P-value = 1.32x10–8 and CTNNA3; OR = 2.43, P-value = 9.40x10–7), exceeding that of most clinical risk factors. We accessed phenome-wide association study (PheWAS) results on both variants. There was no association with other phenotypes for the SYNPO2L variant whereas the CTNNA3 variant showed suggestive association with valvular heart disease (P-value = 2.95x10–5). SYNPO2L and CTNNA3 exhibited high protein and RNA expression levels in atrial tissue and were predominantly expressed in cardiomyocytes (Fig. 1).

Conclusion

We identified novel associations between LOF variation in the structural genes SYNPO2L and CTNNA3 and AF. Our study showed how genetic examination of a European subpopulation facilitates discovery of genetic variants and pathophysiological understanding. The results underline the importance of thoroughly investigating subpopulations as unique variants with large effect sizes can be identified.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): This work was supported by the Research Foundation at Rigshospitalet and the Hallas-Møller Emerging Investigator Novo Nordisk.

Dissecting genetics in hypothyroidism as an independent risk factor in atherosclerotic disease

Background

Thyroid disease comprises a joint group of diseases estimated to affect 10% of the general adult population [1]. Hypothyroidism is characterized by high Thyroid-Stimulating Hormone (TSH) production and low concentrations of Thyroxine (T4). This is known to increase overall mortality and risk of cardiovascular disease (CVD), including heart failure (HF), dyslipidemia, stroke, and coronary artery disease (CAD) [2,3]. Still, the association between CVD and hypothyroidism seems independent of conventional CVD risk factors. This highlights that possible genetic underlying mechanisms remain uncovered and could support CVD monitoring and treatment in patients with hypothyroidism [3]. This study aimed to dichotomize independent genetic mechanisms involved in the increased risk of atherosclerotic disease in patients with hypothyroidism.

Methods

We conducted the largest ever genome-wide association study (GWAS) meta-analysis of hypothyroidism from three European cohorts, which amounted to 71,590 cases and 848,581 controls.

Using Linkage Disequilibrium Regression Score, we highlight novel cardiovascular disease correlations in hypothyroidism. With Mendelian Randomization, we dissected which hypothyroidism-associated Single Nucleotide Polymorphisms (SNPs) infer atherosclerotic disease risk.

Results

We identified 79 novel disease loci in hypothyroidism, and tested 12 correlations which identified novel genetic overlap to CVD (Figure 1). We found five significant correlations to cardiovascular disease and two to cardiometabolic disease. Interestingly, we found overlap to atherosclerotic diseases; CAD (rg=0.16, P=2.12x10–9), HF (rg=0.16, P=1.6x10–5), stroke (rg=0.17, P=1.75x10–3) and aorta aneurysm (rg=0.12, P=3.65x10–3). We also found overlap to triglycerides (rg=0.10, P=1.4x10–5) and a negative correlation to HDL (rg=−0.16, P=8.8x10–11).

Mendelian Randomization suggested hypothyroidism as an independent genetic risk factor with 3% increased risk of CAD (OR=1.03, 95% CI: 1.02–1.04, P=8.1x10–7) and 4% increased risk of myocardial infarction (MI) (OR=1.04, 95% CI: 1.02–1.05, P=3.3x10–6). We identified novel causal SNPs involved in CAD and MI in genes suggesting accelerated atherogenesis, namely; TRIM14 (rs141471464, OR_MI = 1.16 and OR_CAD = 1.10), CTLA4 (rs76749018, OR_MI = 1.10 and OR_CAD = 1.11) (Figure 2).

Conclusions

This analysis highlights novel significant findings between atherosclerotic disease and hypothyroidism. These findings could suggest improving consideration in clinical care for hypothyroid patients at risk of atherosclerotic disease. The genetic findings point towards solid indications, that atherogenesis is frequent and accelerated in this disease. Thus, the usual treatment, monitoring, and prevention strategies, could be reviewed with respect to considering other causal pathways than dyslipidemia for atherosclerotic disease in hypothyroid patients.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The John and Birthe Meyer FoundationVilladsen Family Foundation

The rs13376333 risk allele mimics the effect of atrial fibrillation on SK-current density and afterdepolarizations in human atrial myocytes

Background

Various genome wide association studies have associated the single nucleotide polymorphism (SNP) rs13376333 with increased risk of atrial fibrillation. This SNP is intronic to the KCNN3 gene that codes for the small conductance calcium-activated potassium channel type 3 (SK3), but functional electrophysiological effects of the risk variant are not known.

Purpose

This study aimed to study the effects of atrial fibrillation and the rs13376333 risk SNP on the apamine sensitive SK-current and on afterdepolarizations in human atrial myocytes.

Methods

Myocytes were isolated from human right atrial samples, and subjected to perforated patch-clamp technique to measure the apamine (100 nM) sensitive SK-current elicited by a voltage-ramp protocol, spontaneous transient inward Na-Ca exchange currents (ITI) or afterdepolarizations at rest. To assess the impact of the rs13376333 risk variant, patients without atrial fibrillation were genotyped and divided into risk and control groups according to the genotype at rs13376333.

Results

At membrane potentials above −40 mV, the SK-current density increased with increasing membrane potentials. At +20mV the density was significantly smaller (0.18±0.04 pA/pF) in 5 patients with atrial fibrillation than in 24 patients without this arrhythmia (0.65±0.12 pA/pF, p<0.01). On the other hand, the ITI density was larger in 10 patients with than 23 without atrial fibrillation (0.71±0.16 vs. 0.30±0.03 pA/pF, p<0.01), supporting the notion that a smaller SK-current in myocytes from patients with atrial fibrillation cannot counter-balance the calcium-release induced ITI, resulting in a larger net ITI density and a higher incidence of detectable afterdepolarizations in these patients. In line with this notion, inhibition of the SK-current with 100 nM apamine increased the frequency of afterdepolarization between −85 and −75 mV from 1.2±0.3 to 2.5±0.5 events/min (p=0.03) in patients without atrial fibrillation. Analysis of the current-voltage relationship for the SK-current in atrial myocytes from patients with the rs13376333 risk variant showed that these patients presented a significantly smaller apamine-sensitive SK current (p<0.001, n=15). At +20 mV the SK-density was 60% smaller in patients carrying a rs13376333 risk allele (0.43±0.18 vs. 1.08±0.27 pA/pF) mimicking the depression of the SK-current observed in the patients with atrial fibrillation.

Conclusion

Both the rs13376333 risk allele and atrial fibrillation is associated with a reduced SK-current in human atrial myocytes, which may contribute to the higher incidence of afterdepolarizations in these conditions. Thus, restoration of SK-channel function in patients with a rs1337633 risk SNP or with atrial fibrillation may help reduce the incidence of afterdepolarizations in these patients.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Science and Innovation

Screening for atrial fibrillation to prevent stroke in elderly individuals with or without preexisting cardiovascular disease

Background

Previous research has showed that various cardiovascular diseases (CVD) are associated with increased risks of atrial fibrillation (AF) and stroke. However, data on the interaction between CVD and AF screening efficacy are lacking.

Purpose

To evaluate the influence of preexisting CVD on the effects of AF screening with long-term continuous monitoring.

Methods

The LOOP Study (Atrial Fibrillation detected by Continuous ECG Monitoring using Implantable Loop Recorder to prevent Stroke in High-risk Individuals) randomized AF-naïve individuals aged ≥70 years and with additional stroke risk factors to either long-term screening with implantable loop recorder (ILR) and subsequent anticoagulation initiation upon detection of AF episodes ≥6 minutes, or usual care (the control group). In the current study, all participants from the LOOP Study were divided into two risk groups according to the presence of CVD (defined as ischemic heart disease, heart failure, previous stroke, valvular heart disease, or peripheral artery disease). The relative risks of outcomes in groupwise comparisons, as indicated by hazard ratio (HR), were assessed in the cause-specific Cox proportional-hazards model with death as competing risk.

Results

Of 6004 participants included, 1997 (33.3%) had ≥1 CVD at baseline. Compared with no CVD, the presence of CVD was associated with increased risks of AF diagnosis in the ILR group (adjusted HR 1.32 [1.09–1.59]) and of stroke or systemic arterial embolism in the entire study cohort (adjusted HR 1.34 [1.06–1.69]). For ILR screening versus usual care, there was no decrease in stroke or systemic arterial embolism among participants with preexisting CVD (adjusted HR 1.13 [0.76–1.68]), whereas a significant risk reduction was obtained by screening among those without CVD (adjusted HR 0.64 [0.44–0.93]). The interaction was significant (adjusted p-value for interaction 0.041).

Conclusions

In an elderly, high-risk population, ILR screening did not prevent stroke significantly in individuals with preexisting CVD, but it was associated with an approximately 40% risk reduction among those without CVD.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): The LOOP Study was funded by Innovation Fund Denmark [grant number 12-1352259], The Research Foundation for the Capital Region of Denmark, The Danish Heart Foundation [grant number 11-04-R83-A3363-22625], Aalborg University Talent Management Program, Arvid Nilssons Fond, Skibsreder Per Henriksen, R og Hustrus Fond, the European Union's Horizon 2020 program [grant number 847770], Læge Sophus Carl Emil Friis og hustru Olga Doris Friis' Legat, and an unrestricted grant from Medtronic.

Genome-wide association study on cerebral white-matter hyperintensities in 36,577 individuals

Background/Introduction

A quarter of all strokes are caused by cerebral small vessel disease (CSVD), which is also the most common pathology underlying vascular dementia. [1] White matter hyperintensities (WMH), a radiological marker detectable on magnetic resonance imaging (MRI), can serve as a proxy for CSVD. WMH is associated with stroke, increased risk of dementia and functional decline in older age. [2,3]

Purpose

We aimed at investigating the genetic architecture of WMH using cerebral MRI data.

Methods

We used imaging data ∼40,000 individuals from the UK Biobank, a large population-based, prospective cohort study. We selected individuals with available total volume of WMH from T1 and T2_FLAIR images.

We performed a genome-wide association study (GWAS) on autosomal genetic variants assuming an additive model based on genotype dosages with BOLT-LMM treating WMH as outcome.

We applied LD score regression (LDSC software) to estimate the genetic correlation between WMH traits and traits selected based on availability and relevance for cardiovascular disease.

Results

We included a total of 36,577 individuals with available quality controlled cerebral MRI data.

Genome-wide analysis identified 20 loci of statistical significance, six of which are not previously reported (Fig. 1). Within these novel loci, the following genes are located in proximity to lead variants: EHBP1, OTX1, WDPCP, VCAN, WNT16, FAM3C, ERI1, PRAG1, CACNB2, MTHFSD, FOXL1, FOXC2. Using BOLT, we found the heritability of WMH to be 37%.

We investigated genetic correlation between WMH and multiple phenotypes (Fig. 2). We observed the highest correlation with small vessel stroke (rg=0.56, P=3.9x10–4) Interestingly, WMH was genetically correlated with left atrial volume (rg=0.24, P=2.8x10–3).

Conclusion

In a GWAS on WMH acquired from cerebral MRI, we identified 20 significant loci, of which six are novel. This genetic study provides insights on the biological understanding and epidemiology of CSVD.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): John and Birthe Meyer FoundationThe Hallas-Møller Emerging Investigator Novo Nordisk

High prevalence of deleterious variants in cardiomyopathy genes in patients with early onset atrial fibrillation

Background

Atrial Fibrillation (AF) is a common cardiac arrhythmia associated with increased morbidity and mortality. AF has a significant heritable component and genome-wide association studies have associated numerous loci in the human genome with AF. The arrhythmia is relatively rare in younger individuals, but studies have shown that individuals with early-onset AF may harbour a considerable burden of pathogenic genetic variants.

In recent years, the concept of atrial cardiomyopathy has emerged as a mechanism involved in AF pathogenesis. Genes well-known to be related to ventricular structure, including cardiomyopathies have now also been associated with AF.

Purpose

Using targeted genetic sequencing, this study aimed to elucidate the role of deleterious genetic variants in cardiomyopathy genes in early-onset AF, and provide new insights into AF pathogenesis.

Methods

We performed targeted genetic sequencing of 445 Danish individuals with onset of AF before age 40 years and no other cardiovascular co-morbidities, and of 387 controls with no history of AF. Based on guidelines for genetic testing for clinical use, we focused on 30 genes with well-established associations with dilated cardiomyopathy, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy. We examined the prevalence of loss-of-function variants (defined as variants leading to premature stop-codon, frameshift or splice-site variants), as these are most likely to be disease-causing. We filtered for rare variants using a minor allele frequency <0.1%. The difference in prevalence in the two groups was analyzed using a logistic regression model.

Results

We found that 38 of the 445 early-onset AF patients carried loss-of-function variants in well-established cardiomyopathy genes. The prevalence of rare, loss-of-function variants was enriched in cases compared with controls (8.5%. vs. 1.0%, P=8.27x10–7). The variants were identified in eight different genes, with most rare variants found in the TTN gene (Table 1). In sensitivity analyses excluding TTN variants, we found that 12 individuals (∼2.7%) with AF harbored deleterious loss-of-function variants (P=0.0396).

Conclusions

Individuals with early onset of AF have a considerable burden of rare, deleterious variants in established cardiomyopathy genes. These new insights could help inform future recommendations for genetic testing and follow-up to detect early cardiomyopathy manifestations to prevent adverse outcomes in patients with early onset of AF. These findings support the presence of atrial cardiomyopathy.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Hallas-Møller emerging investigator grant, The Novo Nordisk Foundation (NNF: NNF17OC0031204)The John and Birthe Meyer Foundation

Genome-wide multi-trait analysis on cardioembolic stroke identifies 47 novel loci

Background

Ischemic stroke is one of the leading causes of death and disability-adjusted life-years worldwide. It has several subtypes and cardioembolic stroke (CES) accounts for 15–30% of ischemic strokes. Atrial fibrillation (AF) is the most important risk factor for CES. AF increases the risk of stroke up to 5-fold and there is a substantial overlap in the aetiology of AF and CES. Large genome-wide association studies (GWAS) on AF have identified more than 150 common and rare genetic variants. However, the difficulty in acquiring large sample sizes of CES cohorts has hindered the genetic description of the disease.

Purpose

In this study, we mapped the genetics of CES to increase our understanding of the molecular biology driving the disease. By leveraging the large genetic cohorts of AF through a multi-trait analysis of AF and CES, we aimed to bypass the lack of statistical power for studying the genetics of CES.

Methods

First, we obtained the largest possible sample size of AF GWAS by conducting a meta-analysis on publicly available summary statistics from the FinnGen study (v5) and the largest multi-ethnic meta-analysis on AF to date. Summary statistics for stroke were obtained from the largest multi-ancestry GWAS on stroke to date, MEGASTROKE, which examined different ancestries and stroke subtypes. Multi-trait analysis requires a high genetic correlation. Genetic correlations between the different stroke summary statistics and the AF meta-analysis were assessed with LD Score Regression.

Second, we performed a joint meta-analysis of CES with MTAG using the CES summary statistics from MEGASTROKE and the AF GWAS meta-analysis. MTAG recalculates p-values and effect sizes for each trait separately by leveraging the covariation for correlated traits. The MTAG-computed summary statistics for CES and AF were subjected to genomic loci characterisation, with functional and annotation analysis carried out by FUMA.

Results

We show a high genetic correlation between CES and AF (rg = 0.88). Using MTAG, the GWAS meta-analysis of CES increased the effective sample size by almost 3 folds (n=24,639, Table 1). We discovered 50 CES loci whereof 47 are novel (Fig. 1). We mapped 101 genes to CES MTAG computed summary statistics, obtaining enrichment in gene sets involved in cardiac conduction and contraction, cardiac tissue development and cranial skeleton morphogenesis.

Conclusion

In conclusion, we identified 47 novel CES loci and demonstrated a substantial shared genetic variation with AF. We furthermore mapped 98 genes not previously linked to CES by AF. These results represent findings that potentially could be used for antithrombotic drug discovery and are a major advance in our understanding of the genetic underpinnings of CES

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): John and Birthe Meyer Foundation, the Research Foundation of the Heart Centre, Rigshospitalet, the Research Council at Rigshospitalet.The Hallas-Møller Emerging Investigator Novo Nordisk (NNF17OC0031204), Arvid Nilsson Foundation

Systolic blood pressure and effects of screening for atrial fibrillation with long-term continuous monitoring

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): The LOOP Study was supported by Innovation Fund Denmark [grant number 12-1352259], The Research Foundation for the Capital Region of Denmark, The Danish Heart Foundation [grant number 11-04-R83-A3363-22625], Aalborg University Talent Management Program, Arvid Nilssons Fond, Skibsreder Per Henriksen, R og Hustrus Fond, the European Union’s Horizon 2020 program [grant number 847770 to the AFFECT-EU consortium], Læge Sophus Carl Emil Friis og hustru Olga Doris Friis’ Legat, and an unrestricted grant from Medtronic.

Background

The recently published LOOP Study was a randomized controlled clinical trial to evaluate systematic atrial fibrillation (AF) screening with long-term continuous monitoring in an elderly population at risk and found no significant reduction in stroke. However, the screening effects seemed to differ across levels of systolic blood pressure (SBP). It is well-known that hypertension constitutes a prominent risk factor for clinical AF and stroke alike, but data on the impacts of SBP on subclinical AF and hereby AF screening efficacy are lacking.

Purpose

With this post hoc analysis of the LOOP Study, we aimed to provide insights into the interaction between SBP and benefits of systematic AF screening.

Methods

The LOOP Study randomized individuals aged 70-90 years with ≥1 stroke risk factor (hypertension, diabetes, heart failure, or previous stroke) and without prior AF to either monitoring with implantable loop recorder (ILR) and initiation of oral anticoagulation upon detection of new-onset AF episodes lasting ≥6 minutes, or usual care (control group). In total, 5997 participants with available SBP measurements at enrolment were included in the present analysis. The interaction between SBP and ILR screening efficacy on stroke or systemic arterial embolism (SAE), as indicated by hazard ratio (HR) for ILR versus control, was assessed with polynomial moving-average regression. The lowest SBP threshold with significant screening benefits was further determined and used to examine clinical outcomes and the occurrence of AF with respect to dichotomized SBP. Additionally, penalized spline models were employed to assess AF occurrence by SBP as a continuous variable.

Results

HR of stroke/SAE for ILR versus control decreased with increasing SBP and the lowest threshold for significant screening benefits was at SBP ≥150 mmHg. ILR screening of participants with SBP ≥150 mmHg yielded a 45% risk reduction of stroke/SAE (HR 0.55 [0.37-0.82]). Within the ILR group, SBP ≥150 mmHg was associated with an increased risk of AF episodes ≥24 hours as compared to lower SBP (HR 1.57 [1.01-2.45]), but not with the overall occurrence of AF (HR 1.14 [0.95-1.36]). No significant association between SBP and AF occurrence in the ILR group was reported in penalized spline models either (p-value: 0.73).

Conclusions

The benefits of ILR screening for AF on stroke/SAE increased with increasing blood pressure. SBP ≥150 mmHg was associated with a 1.5-fold increased risk of AF episodes ≥24 hours, along with an almost 50% risk reduction of stroke/SAE by ILR screening.

Integration of Scandinavian genetic data with UK biobank data implicates the RBM20 gene with atrial fibrillation pathogenesis

Purpose

Atrial fibrillation (AF) is the most common sustained arrhythmia. It carries a large healthcare burden and is associated with serious complications. The arrhythmia has a substantial genetic component and is associated with several structural genes, including the gene TTN. A recent large genome-wide association study on AF found an association to RBM20. The RBM20 gene is a splicing factor targeting TTN, RYR2 and CAMK2D among other cardiac genes. Using Next-Generation Sequencing and data derived from the UK Biobank, we aimed to reveal the role of RBM20 in AF.

Methods and results

We examined the burden of rare (Minor allele frequency (MAF)<0.01%) RBM20 loss-of-function (LOF) variants in whole-exome sequencing data from the UK Biobank (n=175,280). AF was defined by ICD9/10, while individuals without AF were used as controls. Association tests aggregating rare variants in RBM20 using the Efficient Variant-Set Mixed Model Association Test (SMMAT) were performed to assess the effect of LOF RBM20 variants, adjusted for age, sex and principal components. We identified 33 LOF variants in RBM20, which were significantly enriched in AF (P=0.0087).

To examine the effect of rare missense RBM20 variants in the splicing of TTN, we screened an in-house cohort of 531 Scandinavian early-onset AF patients using targeted sequencing. We filtered for rare (MAF<0.1%) and deleterious (defined as combined annotation dependent depletion score >20) variants and identified nine missense variants and three novel LOF variants in RBM20. To evaluate the effect of these RBM20 variants, we constructed a series of human RBM20 single nucleotide base exchange mutants. The splicing activity of the variants was measured with RT-qPCR on HEK293 cells transfected with a TTN241–3 splicing reporter. Four of these variants resulted in a significantly altered splicing activity in TTN, with the largest effect observed for LOF variants.

In order to examine the biological effect of RBM20 variants on structural changes in atrial tissue, we used a Norwegian Brown rat animal model with loss of RBM20. In this model, Transmission Electron Microscopy revealed altered sarcomere and mitochondrial structure in its atrial cardiomyocytes. Furthermore, nanopore RNA sequencing of atrial tissue from the aforementioned animal model indicated altered expression in several key cardiac genes, including TTN and PITX2.

Conclusion

Rare RBM20 LOF variants are significantly enriched in AF cases, seen in a large population of 175,000 individuals. We demonstrated that the effect of LOF RBM20 on alternative TTN splicing can be detected on an individual level in patients with AF. Studies using an animal model indicates that LOF in RBM20 may affect atrial function through altered expression of several genes in the atria, and may cause structural changes in the atrial cardiomyocytes. This suggests that RBM20 may be involved in AF pathogenesis mediated through an atrial cardiomyopathy.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Novo Nordisk Foundation Pre-Graduate Scholarships (NNF18OC0053094)The Hallas Møller Emerging Investigator grant (Novo Nordisk Foundation (NNF17OC0031204))

Left atrial remodeling and cerebrovascular disease assessed by magnetic resonance imaging in patients undergoing continuous heart rhythm monitoring

Background

Atrial remodeling and atrial fibrillation (AF) have both been associated with cerebrovascular lesions. We wished to investigate the possible direct association between atrial remodeling and cerebrovascular disease including white matter lesions and lacunar infarcts in patients with and without atrial fibrillation (AF) as documented by implantable loop recorder (ILR).

Methods

Cardiac and cerebral MRI scans were acquired in a cross-sectional study including participants ≥70 years of age with stroke risk factors (history of hypertension, diabetes mellitus, congestive heart failure and/or previous stroke) but without known AF. Cerebrovascular disease was visually rated using the Fazekas scale and number of lacunar strokes. Left atrial (LA) (see figure) and ventricular volumes and function were analyzed, and associations between atrial remodeling and cerebrovascular disease were assessed with logistic regression models. Multivariable models were adjusted for sex, age, diabetes, hypertension, heart failure and history of stroke/transient ischemic attack. The analyses were stratified according to sinus rhythm or any AF during three months of continuous ILR monitoring to account for subclinical AF.

Results

Of 200 participants investigated, 87% had a Fazekas score≥1 and 45% had ≥1 lacunar infarct. Within three months of ILR implantation, AF was detected in 28 (14%) participants, while 172 (86%) had sinus rhythm only. Results are summarized in table. For participants with sinus rhythm, lower LA passive emptying fraction was associated with Fazekas score after multivariable adjustment, while LA total emptying fraction was borderline significant, and increased LA maximum and minimum volumes were associated with lacunar infarcts. There were no significant associations in patients with AF.

Sensitivity analyses showed similar results with longer screening periods for AF.

Conclusions

In patients free from AF as documented by ILR monitoring, we found an independent association between LA passive emptying and Fazekas score, and between atrial volumes and lacunar infarcts. This supports that atrial remodeling alone without AF is associated with an increased risk of cerebrovascular lesions.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): The Innovation Fund, DenmarkThe Research Foundation for the Capital Region of Denmark

Genome-wide association study of atrial fibrillation in 114,539 Finnish individuals reveals novel locus associated with cardiac remodelling

Background/Introduction

Atrial fibrillation (AF) is the most common cardiac arrhythmia and it is associated with serious complications, such as stroke, heart failure, and premature death. Previous genome-wide association studies (GWAS) have associated more than 140 genomic loci with AF; however, these studies predominantly include subjects of European ancestry. Although, the Finnish population is European, it is genetically considered different from other European populations as it has been isolated and developed through multiple bottlenecks followed by population growth. Therefore, pathogenic variants are more easily discovered and heritably diseases are more prevalent.

Methods

We accessed summary statistics on atrial fibrillation and flutter (I48) from the Finngen project. Loci were defined as 1 megabase regions around lead SNPs, and loci were considered novel when the SNPs had P-values <5x10–8 after conditional analysis, and no previously reported SNPs were within the loci. FINEMAP was done with a Finnish LD reference panel, and colocalization of GWAS and eQTL signals were analysed with MetaXcan.

Results

A GWAS on 17,325 Finnish AF cases and 97,214 controls confirms 16 previous identified loci and reveals one novel locus on chromosome 19. The novel lead SNP, rs190065070 (odds ratio [OR] = 1.44, 95% confidence interval [CI] = 1.29–1.61, P-value = 5.96x10–11), is close to the gene EMC10, which encodes the endoplasmic reticulum membrane protein complex subunit 10. While the locus harbours other genes, our MetaXcan analysis could not provide conclusive evidence for other plausible genes. The EMC complex consists of 10 subunits and is a chaperone in endoplasmic reticulum-resident membrane proteins. Previous mouse studies have shown EMC10 to be important in angiogenesis after myocardial infarction, and it has recently been associated with a novel neurodevelopment syndrome. The EMC1 subunit has been associated with congenital heart disease.

Conclusion

We present a novel susceptibility locus associated with AF in the Finnish population. The locus is in proximity to the gene EMC10, which is involved in structural remodelling of the heart after myocardial infarction. These results propose a potentially novel pathophysiological pathway in AF.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): The Research Foundation RigshospitaletThe John and Birthe Meyer Foundation

4259Discovery of the first genome-wide significant risk loci for syncope and collapse

Background

Syncope is a common condition in the general population causing frequent hospitalisation and visits to the emergency department. Family aggregation and twin studies have previously indicated that syncope and collapse has a heritable component.

Purpose

We investigated whether common genetic variants predispose to syncope and collapse.

Methods

We used genome-wide association data on syncope and collapse for 408,961 individuals with European ancestry from the UK Biobank study. In a replication study, the Integrative Psychiatric Research Consortium (iPSYCH) cohort (n=86,189) was used to investigate the risk of incident syncope stratified by genotype carrier status.

Results

We report on a genome-wide significant locus on chromosome 2q32.1 with the lead SNP rs12465214 (odds ratio [OR] = 1.13, 95% confidence interval [CI] = 1.10–1.17, P=5.8x10–15; Figure 1a). This association was replicated in the iPSYCH cohort, where homozygous carriers of the C allele conferred an increased hazard ratio (HR=1.30, CI: 1.15–1.46, P=1.68x10–5; Figure 1b). LD score regression demonstrated a significant genetic correlation (rg) with coronary artery disease (rg=0.41, P=6.99x10–15) and related phenotypes such as angina and hypertension (Figure 1c). Analyses of eQTL (P=4x10–8) and epigenetic chromatin states revealed that variation in this locus likely affects expression of the gene ZNF804A, which resides in its proximity (Figure 1d). A qPCR analysis showed that ZNF804A was mostly expressed in the brain. A lower level of ZNF804A expression was also detected in the cerebral arteries. ZNF804A was not expressed in heart tissue.

Figure 1

Conclusion

rs12465214 is associated with syncope and collapse. Variation in this locus likely modulates the expression of the nearby gene ZNF804A through eQTLs and chromatin interactions. ZNF804A is mainly expressed in the brain and cerebral arteries. However, the precise function of ZNF804A is unknown. Furthermore, syncope and collapse is a polygenetic trait and share a significant genetic overlap with coronary artery disease, angina and hypertension.

Acknowledgement/Funding

This work was supported by grants from The John and Birthe Meyer Foundation, The Research Foundation of the Heart Centre, Rigshospitalet, The Research

P337Natural history, reversibility and arrhythmias associated with truncating titin variants in dilated cardiomyopathy

Background

Truncating genetic variants in titin (TTNtv) are identified in 15–25% of patients with primary dilated cardiomyopathy (DCM). Previous genotype/phenotype studies have reported conflicting results regarding disease severity and pathologic features associated with TTNtv.

Purpose

To investigate the natural history, reversibility and burden of arrhythmias associated with TTNtv in a Danish cohort with long-term follow-up.

Methods

Patients with DCM, recruited from two Danish tertiary centers, were included based on the presence of a TTNtv in a cardiac expressed titin exon. Data on patients' medical history including symptoms, demography, family history, comorbidities, treatment, ECG features, and echocardiograms were registered. Outcome data including all-cause mortality, need of heart transplantation (HTX) or left ventricular assist device (LVAD), and presence of ventricular and supraventricular arrhythmias were registered. Left ventricular reverse remodeling (LVRR) was defined as an absolute increase in left ventricular ejection fraction (LVEF) ≥10% points or normalization.

Results

A total of 104 patients (71 men, 69%; 72 probands) with definite TTNtv-DCM were included. The mean age at DCM diagnosis was (mean±SD) 45±13 years (43±13 for men; 49±14 for women, p<0.04) and median follow-up was 8.1 years. The mean LVEF was 28±13% at time of diagnosis (26±12% for men; 30±13% for women, p=0.173). During follow-up, 31 patients (30%; 24 men) died or needed HTX/LVAD. Medical therapy was associated with LVRR in 79% of patients 3.6 years after diagnosis. LVRR was maintained long-term in 64% of patients. Women had a better response to medical therapy compared to men (mean LVEF increase 19%; vs 15% in men, p<0.04). Atrial fibrillation/flutter was observed in 40% of patients and ventricular arrhythmias in 23% of patients. Men had an earlier occurrence of both supraventricular and ventricular arrhythmias (p=0.005) with half of the men having experienced an arrhythmia at the age of 54 years.

Freedom from arrhythmias with age

Conclusion

TTNtv leads to a DCM phenotype associated with a marked gender-difference in age at DCM diagnosis and high burden of both supraventricular and ventricular arrhythmias. Importantly, the DCM-TTNtv phenotype was associated with a high degree of reversibility of systolic function following medical therapy.

P1231Loss of function in cytoskeletal genes associates with early onset atrial fibrillation

Introduction

Atrial fibrillation (AF) is the most common cardiac arrhythmia. It carries an increased risk of serious complications and an increased mortality. Genome Wide Association Studies have demonstrated that variants in several structural genes are associated with AF, and recently two landmark papers have implicated loss of function (LoF) variants in titin (TTN), a gene associated with dilated cardiomyopathy (DCM), in patients with early onset AF. An atrial cardiomyopathy syndrome has been proposed as a mechanism in the development of AF.

Purpose

We hypothesized that genes encoding structural proteins that were associated with DCM, could also be involved in atrial cardiomyopathy and contribute to AF.

Materials and methods

We performed targeted deep sequencing of structural genes associated with DCM. The genes were grouped by cellular function, and the burden of LoF variants was examined in a cohort of 540 early onset AF patients and compared to a control group (n=383). The patients were below age 49 with normal echo, and no other cardiovascular disease at onset of AF. Patient inclusion in the cohort is still ongoing, and we are working on obtaining a CRISPR/CAS9 modified zebra fish model with LoF variants in cytoskeletal proteins.

Results

We identified a total of 6 carriers of LoF variants in 3 genes thought to encode cytoskeletal proteins (DMD, PDLIM3 and FKTN). The burden of variants in cytoskeletal genes was significantly increased in patients with early onset AF compared with controls (p=0.0385). Four carriers had LoF variants in the dystrophin gene (DMD), while there was 1 carrier of LoF variants in PDLIM3 and FKTN respectively. All carriers with LoF variants in DMD developed persistent AF before age 30.

Conclusion

Our data suggest that rare mutations in cytoskeletal genes previously associated with DCM, may also play a role in the development of early onset AF. The data supports that AF is a part of an atrial cardiomyopathy syndrome.

Acknowledgement/Funding

Novo Nordisk Fonden Pre-Graduate Scholarships

Distinguishing pathogenic mutations from background genetic noise in cardiology: The use of large genome databases for genetic interpretation

Advances in clinical genetic testing have led to increased insight into the human genome, including how challenging it is to interpret rare genetic variation. In some cases, the ability to detect genetic mutations exceeds the ability to understand their clinical impact, limiting the advantage of these technologies. Obstacles in genomic medicine are many and include: understanding the level of certainty/uncertainty behind pathogenicity determination, the numerous different variant interpretation-guidelines used by clinical laboratories, delivering the certain or uncertain result to the patient, helping patients evaluate medical decisions in light of uncertainty regarding the consequence of the findings. Through publication of large publicly available exome/genome databases, researchers and physicians are now able to highlight dubious variants previously associated with different cardiac traits. Also, continuous efforts through data sharing, international collaborative efforts to develop disease-gene-specific guidelines, and computational analyses using large data, will indubitably assist in better variant interpretation and classification. This article discusses the current, and quickly changing, state of variant interpretation resources within cardiovascular genetic research, e.g., publicly available databases and ways of how cardiovascular genetic counselors and geneticists can aid in improving variant interpretation in cardiology.

Integration of 60,000 exomes and ACMG guidelines question the role of Catecholaminergic Polymorphic Ventricular Tachycardia-associated variants

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a highly lethal cardiac arrhythmia disease occurring during exercise or psychological stress. CPVT has an estimated prevalence of 1:10,000 and has mainly been associated with variants in calcium-regulating genes. Identification of potential false-positive pathogenic variants was conducted by searching the Exome Aggregation Consortium (ExAC) database (n = 60,706) for variants reported to be associated with CPVT. The pathogenicity of the interrogated variants was assessed using guidelines from the American College of Medical Genetics and Genomics (ACMG) and in silico prediction tools. Of 246 variants 38 (15%) variants previously associated with CPVT were identified in the ExAC database. We predicted the CPVT prevalence to be 1:132. The ACMG standards classified 29% of ExAC variants as pathogenic or likely pathogenic. The in silico predictions showed a reduced probability of disease-causing effect for the variants identified in the exome database (p < 0.001). We have observed a large overrepresentation of previously CPVT-associated variants in a large exome database. Based on the frequency of CPVT in the general population, it is less likely that the previously proposed variants are associated with a highly penetrant monogenic form of the disease.

High prevalence of genetic variants previously associated with Brugada syndrome in new exome data

More than 300 variants in 12 genes have been associated with Brugada syndrome (BrS) which has a prevalence ranging between 1:2000 and 1:100,000. Until recently, there has been little knowledge regarding the distribution of genetic variations in the general population. This problem was partly solved, when exome data from the NHLI GO Exome Sequencing Project (ESP) was published. In this study, we aimed to report the prevalence of previously BrS-associated variants in the ESP population. We performed a search in ESP for variants previously associated with BrS. In addition, four variants in ESP were genotyped in a second Danish control population (n = 536) with available electrocardiograms. In ESP, we identified 38 of 355 (10%) variants, distributed on 272 heterozygote carriers and two homozygote carriers. The genes investigated were on average screened in 6258 individuals. This corresponds to a surprisingly high genotype prevalence of 1:23 (274:6258). Genotyping the four common ESP-derived variants CACNA2D1 S709N, SCN5A F2004L, CACNB2 S143F, and CACNB2 T450I in the Danish controls, we found a genotype prevalence comparable with that found in ESP. We suggest that exome data are used in research, as an additive tool to predict the pathogenicity of variants in patients suspected for BrS.