Early-onset Atrial Fibrillation Research Articles

Genetics of atrial fibrillation-practical applications for clinical management: if not now, when and how?

The prevalence and economic burden of atrial fibrillation (AF) are predicted to more than double over the next few decades. In addition to anticoagulation and treatment of concomitant cardiovascular conditions, early and standardized rhythm control therapy reduces cardiovascular outcomes as compared with a rate control approach, favouring the restoration, and maintenance of sinus rhythm safely. Current therapies for rhythm control of AF include antiarrhythmic drugs (AADs) and catheter ablation (CA). However, response in an individual patient is highly variable with some remaining free of AF for long periods on antiarrhythmic therapy, while others require repeat AF ablation within weeks. The limited success of rhythm control therapy for AF is in part related to incomplete understanding of the pathophysiological mechanisms and our inability to predict responses in individual patients. Thus, a major knowledge gap is predicting which patients with AF are likely to respond to rhythm control approach. Over the last decade, tremendous progress has been made in defining the genetic architecture of AF with the identification of rare mutations in cardiac ion channels, signalling molecules, and myocardial structural proteins associated with familial (early-onset) AF. Conversely, genome-wide association studies have identified common variants at over 100 genetic loci and the development of polygenic risk scores has identified high-risk individuals. Although retrospective studies suggest that response to AADs and CA is modulated in part by common genetic variation, the development of a comprehensive clinical and genetic risk score may enable the translation of genetic data to the bedside care of AF patients. Given the economic impact of the AF epidemic, even small changes in therapeutic efficacy may lead to substantial improvements for patients and health care systems.

Association of Rare Genetic Variants and Early-Onset Atrial Fibrillation in Ethnic Minority Individuals

Although rare variants in cardiac ion channels, transcription factors, and myocardial structural proteins are associated with early-onset atrial fibrillation (AF) in White individuals of European descent, it remains unclear whether genetic variation also contributes to the cause of AF in those of minority ethnicity. To assess the prevalence of rare and novel pathogenic variants in candidate genes in ethnic minority probands with early-onset AF and determine genotype-phenotype associations. In this cohort, family-based study, probands of African and Hispanic descent with early-onset AF (defined as AF occurring in individuals aged ≤66 years) prospectively enrolled in a clinical and genetic biorepository underwent sequencing of 60 candidate genes. Recruitment took place from July 1, 2015, to June 30, 2019. Data were analyzed from February 1 to February 28, 2020. Rare and novel variants categorized as pathogenic or likely pathogenic. The prevalence of rare and novel pathogenic variants in African American and Hispanic/Latinx probands with early-onset AF and genotype-phenotype associations. Among 227 probands with early-onset AF, mean (SD) age at onset of AF was 51.0 (9.9) years, 132 probands (58.1%) were men, 148 (65.2%) were African American, and 79 (34.8%) were Hispanic/Latinx. A family history of AF was verified in 24 probands with early-onset AF (10.6%). Sequencing 60 candidate genes identified 53 (23 rare and 30 novel) variants with 16 of the 227 (7.0%) probands harboring likely pathogenic (43.8%) or pathogenic (56.2%) variants, with most loss-of-function variants in TTN, the gene encoding the sarcomeric protein titin (46.7%). In 6 families with more than 2 affected members, variants of unknown significance in sodium channel (SCN10A), potassium channel (KCNE5), sarcomeric proteins (MYH6 and TTN), and atrial natriuretic peptide (NPPA) cosegregated with AF. In this study, likely pathogenic and pathogenic variants were identified, with most loss-of-function variants in TTN, that increase susceptibility to early-onset AF in African American and Hispanic/Latinx individuals. These findings provide further understanding toward molecular phenotyping of AF and suggest novel mechanism-based therapeutic approaches for this common arrhythmia in ethnic minority groups.

The International Society for Biological and Environmental Repositories Presents Abstracts from Its 2021 Annual Meeting Connect and Collaborate through Biobanking: Powering Innovation and Discovery May 10–14, 2021

The International Society for Biological and Environmental Repositories Presents Abstracts from Its 2021 Annual Meeting Connect and Collaborate through Biobanking: Powering Innovation and Discovery May 10–14, 2021

Abstract 16403: Prevalence and Sex Differences in Early-onset Atrial Fibrillation - A Nation-wide Primary Care Study in Norway

Background: Several studies have reported a male:female ratio of 4:1 in lone atrial fibrillation (AF) populations. However, there have been few reports on the young population with AF, and no reports from a primary care setting. Here, we describe prevalence and sex-differences in early-onset AF in a nation-wide register-based study in the primary care sector in Norway. Methods: In Norway, with a population of 5.4 million, healthcare is publicly financed and all general practitioner (GP) claims have been recorded in the Norwegian Control and Payment of Health Reimbursement (KUHR) registry, since 2006. We identified all individuals aged ≥18 and <50 years registered with ≥1 AF diagnosis code (International Classification of Primary Care (ICPC) K78), from 2006-2019 in the KUHR registry. Based on population estimates from Statistics Norway, we calculated the prevalence of early-onset AF in 2019, as a total, by sex, and by age groups: 18-29, 30-39, 40-49. Results: We identified 5563 individuals (28.5% women, age 18-49 years) aged 18-49 in 2019 with AF diagnosed <age 50 years. In 2019, the prevalence of early-onset AF registered in all individuals up to age 50 was 0.24% (women: 0.14% (1585/1114821), men 0.34% (3978/1176555), p=1.4x10 -205 ) with a ratio of 2.5 men:women. In individuals aged 18-29 the prevalence was 0.05% (women 0.04% (164/410367), men 0.07% (292/435001), p=79x10 -8 ). For the age group 30-39 years the prevalence was 0.19% (women 0.12% (408/349639), men 0.27% (985/367730), p=3.9x10 -49 ). For the age group 40-49 years the prevalence was 0.51% (women 0.29% (1013/354815), men 0.72% (2701/373824), p=1.39x10 -155 ). Conclusion: We show that the prevalence of early-onset AF in a nation-wide primary care population is 0.24% and that the sex-difference in prevalence is smaller than previously reported in early-onset and lone AF studies. Our findings underline the need of increased awareness of AF as a disease in the young, and particularly to women in the youngest age-groups.

Abstract 16553: Association Between Family History and Isolated Early-Onset Atrial Flutter Across Race-Ethnicity

Introduction: There is a genetic predisposition to early-onset atrial fibrillation (EOAF) but the role of family history in the pathogenesis of isolated EO atrial flutter (AFL) across racial and ethnic minorities remains unclear. Here, we determined whether probands with isolated EOAFL across race and ethnicity have a higher rate of AF in first-degree family members than matched control patients with late-onset (LO) AFL. Methods: In this cohort study, patients prospectively enrolled in a clinical and genetic biorepository were administered baseline questionnaires that included questions about family history of AFL. EOAFL was defined as AFL occurring in probands aged 60 years or younger in the absence of structural heart disease. All other forms were categorized as LOAFL. The main outcome measure was the reported family history of AFL in first-degree relatives. Results: Of 106 patients enrolled, 23 (23%) were European American; 53 (52%) were African American, 22 (22%) were Hispanic/Latino (H/L) and 3 (3%) were Asian American. There was a family history of AFL in 11 probands with EOAFL (18%) compared with 3 (7%) patients with LOAFL (Table 1). There was a significantly greater prevalence of CHF in the EOAFL group (40%) than the LOAFL group (21%). Conclusion: Probands with isolated EOAFL are more likely to have a first-degree relative with AFL when compared to matched controls with isolated LOAFL. Our findings support genetic predisposition to isolated EOAFL across racial and ethnic minorities.

Abstract 16184: Lamin A Deficiency Leads to Electrophysiological and Nuclear Abnormalities Reminiscent of Atrial Cardiomyopathy in Zebrafish

Introduction: Mutations in the lamin A/C ( LMNA ) gene have been causally linked to atrial arrhythmias and cardiac conduction disease (CCD) in young adults. However, the mechanism by which the laminopathy leads to perturbed cardiac electrophysiology has not been fully elucidated. Hypothesis: We hypothesize that protein-truncating variants in LMNA will impair the mechano-protection force in the nuclear envelope and will lead to early-onset cardiomyocyte degeneration and CCD. Methods: In a multi-regional registry of early-onset CCD and atrial fibrillation in Japan, we performed whole-exome DNA sequencing of 23 probands. Using CRISPR/Cas9, we generated indels of candidate gene homologues in zebrafish and characterized cardiac physiology using optical mapping technology and immunohistochemistry. Results: Among all probands, our study revealed four rare nonsense variants in the nuclear protein-coding genes. We focused on a LMNA protein-truncating variant, c.339dupT (p.K114X fsX1), and created a variant in the zebrafish lmna that produced a similar truncation. Lmna -/- zebrafish larvae showed shortened atrial action potential duration (APD) (msec.) compared to wild-type controls (162 ± 19 vs 227 ± 79, p<0.05), while conduction velocities (CV) did not vary between the genotypes. In contrast, the atrioventricular canal of lmna -/- embryos exhibited prolonged APD (399 ± 51 vs 322 ± 47, p<0.05) and slower CV (mm/sec.) (0.37 ± 0.12 vs 0.57 ± 0.12, p<0.05) than controls. Immunohistochemistry demonstrated that atrial cardiomyocytes of embryonic lmna -/- zebrafish displayed significantly decreased cell numbers and smaller cell size compared to those of controls, which in turn developed into abnormal nuclear structures in adult. Conclusions: These findings suggest that lamin A is a prerequisite for proper atrial cardiomyocyte morphology in embryonic zebrafish, and is indispensable for correct cardiac electrophysiology and -conduction.

Sequencing candidate genes in African American and Hispanic/ Latino probands with early-onset Atrial Fibrillation

Abstract Introduction Mutations in cardiac ion channels, structural proteins and signaling molecules have been identified in European whites with early-onset AF (EOAF). However, it remains unclear if genetic variation also contributes to the etiology of EOAF in ethnic minorities. Purpose To determine the prevalence of disease causing variants in candidate AF genes in African American and Hispanic/Latino probands with EOAF. Method In this family-based study, probands of African and Hispanic descent with EOAF (defined as AF ≤65 years) were prospectively enrolled in a clinical-DNA biorepository and underwent targeted sequencing for 60 AF candidate genes. Variants were filtered at 20X read depth and clinically evaluated with American College of Medical Genetics and Genomics and Association for Molecular Pathology (ACMG/AMP) as well as the Association for Clinical Genomic Science (ACGS) criteria for disease-causing mutations. Results Among 227 EOAF probands with mean (SD) age of AF 51.0 (9.9) years, 132 (58.0%) were men and 148 (65.0%) African American and 79 (35.0%) Hispanic/Latino. Sequencing 60 candidate AF genes revealed 90 variants that met filtering criteria and underwent clinical evaluation. We identified 16 (7.0%) EOAF probands with a likely pathogenic or pathogenic variant with the majority being loss of function (62.5%) and located in the TTN gene (50.0%). We confirmed a family history of AF in 24 probands (10.6%) and 6 families with >1 affected member a variant of unknown significance (VUS) in genes encoding for a sodium channel (SCN10A), potassium channel (KCNE5), sarcomeric proteins (MYH6, TTN) and atrial natriuretic peptide (NPPA) co-segregated with AF. Conclusion Gene sequencing in African American and Hispanic/Latinos probands with EOAF identified a small percentage of disease causing variants in patients with EOAF. Our findings not only represent important progress toward molecular phenotyping of EOAF, but also provides insight into the underlying pathophysiology toward targeted mechanism-based therapies for AF in ethnic minorities. Funding Acknowledgement Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): American Heart Association

Prevalence and incidence rates of atrial fibrillation in Norway 2004–2014

ObjectiveTo study time trends in incidence of atrial fibrillation (AF) in the entire Norwegian population from 2004 to 2014, by age and sex, and to estimate the prevalence of AF...

Short-term anticoagulation after acute cardioversion of early-onset atrial fibrillation.

Controversy exists regarding anticoagulation management following acute cardioversion in patients with early-onset (<48hours) atrial fibrillation without class I guideline indication for long-term oral anticoagulation (CHA2DS2-VASc 0-1). A random-effect meta-analysis of observational studies reporting 30-day incidence of thromboembolic complications after cardioversion without post-procedural oral anticoagulation therapy in patients at low-moderate thromboembolic risk (CHA2DS2-VASc 0-1) was performed. Four studies were included, encompassing 3276 cardioversions. The analysis revealed that the pooled risk of 30-day incidence of thromboembolic complications in this subset of patients is low (0.10%, 95% confidence interval: 0.00%-0.30%). Given these data, considering the bleeding risk unavoidably conferred by OAT, which is known to be higher in the first month from treatment onset, short-term anticoagulation limited to 4weeks post-cardioversion of early-onset (<48hours) atrial fibrillation in patients with low-moderate risk of stroke (CHA2DS2-VASc 0-1) may be omitted, at least in patients with high-bleeding risk.

Early-onset atrial fibrillation patients show reduced left ventricular ejection fraction and increased atrial fibrosis

Atrial fibrillation (AF) has traditionally been considered an electrical heart disease. However, genetic studies have revealed that the structural architecture of the heart also play a significant role. We evaluated the functional and structural consequences of harboring a titin-truncating variant (TTNtv) in AF patients, using cardiac magnetic resonance (CMR). Seventeen early-onset AF cases carrying a TTNtv, were matched 1:1 with non-AF controls and a replication cohort of early-onset AF cases without TTNtv, and underwent CMR. Cardiac volumes and left atrial late gadolinium enhancement (LA LGE), as a fibrosis proxy, were measured by a blinded operator. Results: AF cases with TTNtv had significantly reduced left ventricular ejection fraction (LVEF) compared with controls (57 ± 4 vs 64 ± 5%, P < 0.001). We obtained similar findings in early-onset AF patients without TTNtv compared with controls (61 ± 4 vs 64 ± 5%, P = 0.02). We furthermore found a statistically significant increase in LA LGE when comparing early-onset AF TTNtv cases with controls. Using state-of-the-art CMR, we found that early-onset AF patients, irrespective of TTNtv carrier status, had reduced LVEF, indicating that early-onset AF might not be as benign as previously thought.

Identification of a New Gain-of-Function Mutation of NaV1.5 Associated with Atrial Fibrillation in an African-American Family

Mutations and rare genetic variants in cardiac voltage-gated Nav1.5 channel, have been associated with inherited predisposition to ventricular arrhythmias such as in long QT syndrome and Brugada syndrome. More recently, Nav1.5 mutations have been identified in families segregating atrial fibrillation (AF), the most common arrhythmia in adults. Here, we evaluated the functional and biophysical properties of an Nav1.5 mutation associated with early-onset AF in an African-American family. The African-American proband presented with early-onset AF with controlled ventricular rates on no AV nodal blockers strongly implicating conduction disease.

Loss-of-Function Variants in Cytoskeletal Genes Are Associated with Early-Onset Atrial Fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and it is associated with an increased risk of heart failure, stroke, dementia, and death. Recently, titin-truncating variants (TTNtv), which are predominantly associated with dilated cardiomyopathy (DCM), were associated with early-onset AF. Furthermore, genome-wide association studies (GWAS) associated AF with other structural genes. In this study, we investigated whether early-onset AF was associated with loss-of-function variants in DCM-associated genes encoding cytoskeletal proteins. Using targeted sequencing, we examined a cohort of 527 Scandinavian individuals with early-onset AF and a control group of individuals free of AF (n = 383). The patients had onset of AF before 50 years of age, normal echocardiogram, and no other cardiovascular disease at onset of AF. We identified six individuals with rare loss-of-function variants in three different genes (dystrophin (DMD), actin-associated LIM protein (PDLIM3), and fukutin (FKTN)), of which two variants were novel. Loss-of-function variants in cytoskeletal genes were significantly associated with early-onset AF when patients were compared with controls (p = 0.044). Using publicly available GWAS data, we performed genetic correlation analyses between AF and 13 other traits, e.g., showing genetic correlation between AF and non-ischemic cardiomyopathy (p = 0.0003). Our data suggest that rare loss-of-function variants in cytoskeletal genes previously associated with DCM may have a role in early-onset AF, perhaps through the development of an atrial cardiomyopathy.

The Effects of Single Nucleotide Polymorphisms in Korean Patients with Early-onset Atrial Fibrillation after Catheter Ablation.

BackgroundThis study evaluated the status of single nucleotide polymorphisms (SNPs) in Korean patients with early-onset (< 40 years old) atrial fibrillation (AF) and their effects on the outcome after catheter ablation.MethodsA total of 89 patients (35.7 ± 3.7 years, 81 males) with drug-refractory AF (paroxysmal 64.0%) who underwent catheter ablation were included in this study. Sixteen SNPs, including rs13376333, rs10465885, rs10033464, rs2200733, rs17042171, rs6843082, rs7193343, rs2106261, rs17570669, rs853445, rs11708996, rs6800541, rs251253, rs3807989, rs11047543, and rs3825214, were genotyped. Serial 48-hour Holter monitoring was conducted to detect AF recurrences during long-term follow up.ResultsWild-type genotypes of rs11047543 (GG; 26/69 [37.7%] vs. GA; 13/18 [72.2%] vs. AA; 0/0 [0%], P = 0.009) and rs7193343 (CC; 0/7 [0%] vs. CT; 22/40 [55.0%] vs. TT; 18/41 [43.9%], P = 0.025) and the homozygous variant of rs3825214 (AA; 16/31 [51.6%] vs. AG; 22/43 [51.2%] vs. GG; 2/13 [15.4%], P = 0.056) were significantly associated with a lower rate of late recurrence. When the patients were assigned to four groups according to the number of risk alleles (n = 0–3), there were significant differences in recurrence rate (n = 0; 0/3 vs. n = 1; 2/13 [15.4%] vs. n = 2; 24/52 [46.2%] vs. n = 3; 13/17 [76.5%], P = 0.003). When correcting for multiple variables, rs11047543 (hazard ratio [HR], 2.723; 95% confidence interval [CI], 1.358–5.461; P = 0.005) and the number of risk alleles (HR, 2.901; 95% CI, 1.612–5.219; P < 0.001) were significantly associated with recurrence of AF after catheter ablation.ConclusionPolymorphisms on rs7193343 closest to ZFHX3 (16q22), rs3825214 near to TBX5 (12q24), and rs11047543 near to SOX5 (12p12) modulate the risk for AF recurrence after catheter ablation. The number of risk alleles of these 3 SNPs was an independent predictor of recurrence during long-term follow up in Korean patients with early-onset AF.

Monogenic and Polygenic Contributions to Atrial Fibrillation Risk

Genome-wide association studies have identified over 100 genetic loci for atrial fibrillation (AF); recent work described an association between loss-of-function (LOF) variants in TTN and early-onset AF. We sought to determine the contribution of rare and common genetic variation to AF risk in the general population. The UK Biobank is a population-based study of 500 000 individuals including a subset with genome-wide genotyping and exome sequencing. In this case-control study, we included AF cases and controls of genetically determined white-European ancestry; analyses were performed using a logistic mixed-effects model adjusting for age, sex, the first 4 principal components of ancestry, empirical relationships, and case-control imbalance. An exome-wide, gene-based burden analysis was performed to examine the relationship between AF and rare, high-confidence LOF variants in genes with ≥10 LOF carriers. A polygenic risk score for AF was estimated using the LDpred algorithm. We then compared the contribution of AF polygenic risk score and LOF variants to AF risk. The study included 1546 AF cases and 41 593 controls. In an analysis of 9099 genes with sufficient LOF variant carriers, a significant association between AF and rare LOF variants was observed in a single gene, TTN (odds ratio, 2.71, P=2.50×10-8). The association with AF was more significant (odds ratio, 6.15, P=3.26×10-14) when restricting to LOF variants located in exons highly expressed in cardiac tissue (TTNLOF). Overall, 0.44% of individuals carried TTNLOF variants, of whom 14% had AF. Among individuals in the highest 0.44% of the AF polygenic risk score only 9.3% had AF. In contrast, the AF polygenic risk score explained 4.7% of the variance in AF susceptibility, while TTNLOF variants only accounted for 0.2%. Both monogenic and polygenic factors contribute to AF risk in the general population. While rare TTNLOF variants confer a substantial AF penetrance, the additive effect of many common variants explains a larger proportion of genetic susceptibility to AF.

4183New onset atrial fibrillation in acute coronary syndrome: early vs late onset

Abstract Background The prognostic impact of the timing where new-onset Atrial Fibrillation (AF) occurs in Acute Coronary Syndrome (ACS) patients isn't well studied. Objective Evaluate the predictors and prognostic impact of early-onset AF (EAF) and late-onset AF (LAF) in ACS patients. Methods We analysed 17016 patients with ACS enrolled in a national multicenter registry from October 2010 to January 2019. Patients with history of valvular disease, valve replacement, AF present at hospital admission or those who died in the first 48 hours were excluded. EAF was defined as AF in the first 48 hours of hospitalization and LAF after 48 hours. The primary endpoint was a composite of death and readmission from cardiovascular causes at 1 year. Results The mean age was 65±13 years; 74% were males and 42% had STEMI). 324 (1.9%) had EAF and 344 (2.0%) had LAF. The predictors of EAF were age ≥75 years (OR 2.04, 95% CI 1.53–2.70, p&lt;0.001); history of heart failure (OR 1.82, 95% CI 1.09–3.02, p=0.022), STEMI diagnosis (OR 2.74, 95% CI 2.06–3.61, p&lt;0.001), admission Killip class (KK)≥2 (OR 2.70, 95% CI 1.98–3.69, p&lt;0.001). The predictors of LAF were age ≥75 years (OR 3.15, 95% CI 2.36–4.19, p&lt;0.001), history of stable angina (OR 1.42, 95% CI 1.06–1.90, p=0.018), cerebrovascular disease (OR 1.68, 95% CI 1.14–2.46, p=0.008), COPD (OR 2.33, 95% CI 1.58–3.44, p&lt;0.001), STEMI diagnosis (OR 2.31, 95% CI 1.77–3.03, p&lt;0.001), admission KK ≥2 (OR 2.06, 95% CI 1.54–2.76, p&lt;0.001) and stress hyperglycemia (OR 1.54, 95% CI 1.15–2.05, p=0.003) In STEMI patients only those with LAF had higher symptoms time (245 (IQR 165–400) minutes vs 284 (IQR 200–425) min; p=0.02). During hospitalization, LAF patients had a worse prognosis with a higher rate of heart failure, re-infarction, stroke, major bleeding and death (Table 1). In the follow-up, in multivarite analysis, only LAF was a predictor of the primary endpoint (EAF: HR 0.79, 95% CI 0.50–1.25, p=0.314; LAF: HR 1.45, 95% CI 1.05–2.00, p&lt;0.025). Complications during hospitalization No AF EAF LAF p Death 1.3 6.5 12.5 &lt;0.001 Heart Failure 11.4 38.3 50.3 &lt;0.001 Re-enfarction 1.0 0.9 3.5 &lt;0.001 Stroke 0.5 0.9 3.8 &lt;0.001 Major bleeding 1.3 4.3 4.1 &lt;0.001 Kaplan Meier curve Conclusion Patients with EAF and LAF have different characteristics and outcomes with LAF patients having a worse in-hospital and long term prognosis.

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

Abstract 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

Functional Characterization of Rare Variants in the SHOX2 Gene Identified in Sinus Node Dysfunction and Atrial Fibrillation.

Sinus node dysfunction (SND) and atrial fibrillation (AF) often coexist; however, the molecular mechanisms linking both conditions remain elusive. Mutations in the homeobox-containing SHOX2 gene have been recently associated with early-onset and familial AF. Shox2 is a key regulator of sinus node development, and its deficiency leads to bradycardia, as demonstrated in animal models. To provide an extended SHOX2 gene analysis in patients with distinct arrhythmias, we investigated SHOX2 as a susceptibility gene for SND and AF by screening 98 SND patients and 450 individuals with AF. The functional relevance of the novel mutations was investigated in vivo and in vitro, together with the previously reported p.H283Q variant. A heterozygous missense mutation (p.P33R) was identified in the SND cohort and four heterozygous variants (p.G77D, p.L129=, p.L130F, p.A293=) in the AF cohort. Overexpression of the pathogenic predicted mutations in zebrafish revealed pericardial edema for p.G77D and the positive control p.H283Q, whereas the p.P33R and p.A293= variants showed no effect. In addition, a dominant-negative effect with reduced heart rates was detected for p.G77D and p.H283Q. In vitro reporter assays demonstrated for both missense variants p.P33R and p.G77D significantly impaired transactivation activity, similar to the described p.H283Q variant. Also, a reduced Bmp4 target gene expression was revealed in zebrafish hearts upon overexpression of the p.P33R mutant. This study associates additional rare variants in the SHOX2 gene implicated in the susceptibility to distinct arrhythmias and allows frequency estimations in the AF cohort (3/990). We also demonstrate for the first time a genetic link between SND and AF involving SHOX2. Moreover, our data highlight the importance of functional investigations of rare variants.

Genetic variants on chromosomes 7p31 and 12p12 are associated with abnormal atrial electrical activation in patients with early-onset lone atrial fibrillation.

Abnormal P-wave morphology (PWM) has been associated with a history of atrial fibrillation (AF) in earlier studies. Although lone AF is believed to have substantial genetic basis, studies on associations between single nucleotide polymorphisms (SNP) linked to lone AF and PWM have not been reported. We aimed to assess whether SNPs previously associated with lone AF (rs2200733, rs13376333, rs3807989, and rs11047543) are also linked to P-wave abnormalities. Four SNPs were studied in 176 unrelated individuals with early-onset lone AF (age at onset <50years), median age 38years (19-63years), 149 men. Using sinus rhythm ECG, orthogonal PWM was classified as Type 1-positive in leads X and Y and negative in lead Z, Type 2-positive in leads X and Y and biphasic (-/+) in lead Z, Type 3-positive in lead X and biphasic in lead Y (+/-), and the remaining as atypical. Two SNPs were found to be significantly associated with altered P-wave morphology distribution: rs3807989 near the gene CAV1/CAV2 and rs11047543 near the gene SOX5. Both SNPs were associated with a higher risk of non-Type 1 P-wave morphology (rs3807989: OR=4.8, 95% CI=2.3-10.2, p<0.001; rs11047543: OR=4.7, 95% CI=1.1-20.5, p=0.04). No association was observed for rs2200733 and rs13376333. In this study, the two variants rs3807989 and rs11047543, previously associated with PR interval and lone AF, were associated with altered P-wave morphology distribution in patients with early-onset lone AF. These findings suggest that common genetic variants may modify atrial conduction properties.

Association Between Titin Loss-of-Function Variants and Early-Onset Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia affecting 1% of the population. Young individuals with AF have a strong genetic association with the disease, but the mechanisms remain incompletely understood. To perform large-scale whole-genome sequencing to identify genetic variants related to AF. The National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine Program includes longitudinal and cohort studies that underwent high-depth whole-genome sequencing between 2014 and 2017 in 18 526 individuals from the United States, Mexico, Puerto Rico, Costa Rica, Barbados, and Samoa. This case-control study included 2781 patients with early-onset AF from 9 studies and identified 4959 controls of European ancestry from the remaining participants. Results were replicated in the UK Biobank (346 546 participants) and the MyCode Study (42 782 participants). Loss-of-function (LOF) variants in genes at AF loci and common genetic variation across the whole genome. Early-onset AF (defined as AF onset in persons <66 years of age). Due to multiple testing, the significance threshold for the rare variant analysis was P = 4.55 × 10-3. Among 2781 participants with early-onset AF (the case group), 72.1% were men, and the mean (SD) age of AF onset was 48.7 (10.2) years. Participants underwent whole-genome sequencing at a mean depth of 37.8 fold and mean genome coverage of 99.1%. At least 1 LOF variant in TTN, the gene encoding the sarcomeric protein titin, was present in 2.1% of case participants compared with 1.1% in control participants (odds ratio [OR], 1.76 [95% CI, 1.04-2.97]). The proportion of individuals with early-onset AF who carried a LOF variant in TTN increased with an earlier age of AF onset (P value for trend, 4.92 × 10-4), and 6.5% of individuals with AF onset prior to age 30 carried a TTN LOF variant (OR, 5.94 [95% CI, 2.64-13.35]; P = 1.65 × 10-5). The association between TTN LOF variants and AF was replicated in an independent study of 1582 patients with early-onset AF (cases) and 41 200 control participants (OR, 2.16 [95% CI, 1.19-3.92]; P = .01). In a case-control study, there was a statistically significant association between an LOF variant in the TTN gene and early-onset AF, with the variant present in a small percentage of participants with early-onset AF (the case group). Further research is necessary to understand whether this is a causal relationship.

A Novel PITX2c Gain-of-Function Mutation, p.Met207Val, in Patients With Familial Atrial Fibrillation

Genome-wide studies have associated several genetic variants upstream of PITX2 on chromosome 4q25 with atrial fibrillation (AF), suggesting a potential role of PITX2 in AF. Our study aimed at identifying rare coding variants in PITX2 predisposing to AF. The Polymerase chain reaction sequencing of PITX2c was performed in 60 unrelated patients with idiopathic AF. The p.Met207Val variant was identified in 1 of 60 French patients with early onset AF and in none of 389 French referents. This variant, located in the inhibitory domain 1 distal to the homeodomain, was evaluated by the software MutationTaster as a disease-causing mutation with a probability of 0.999. Reporter gene assays demonstrated that p.Met207Val caused a 3.1-fold increase in transactivation activity of PITX2c in HeLa cells in comparison with its wild-type counterpart. When the variant was coexpressed with wild-type PITX2c in the HL-1 immortalized mouse atrial cell line, this gain-of-function caused an increase in the mRNA level of KCNH2 (2.6-fold), SCN1B (1.9-fold), GJA5 (3.1-fold), GJA1 (2.1-fold), and KCNQ1 in the homozygous form (1.8-fold). These genes encode for the IKr channel α subunit, the β-1 Na+ channel subunit, connexin 40, connexin 43 and the IKs channel α subunit, respectively. These conditions may contribute to the propensity to AF found in patients carrying the p.Met207Val variant. In conclusion, the present report is the first to associate a gain-of-function mutation of PITX2c with increased vulnerability to AF, therefore, restoration of normal PITX2c function may be a potential therapeutic target in AF patients.