Genetic variants in TRPM7 associated with unexplained stillbirth modify ion channel function

Stillbirth is the loss of a fetus after 22 weeks of gestation, of which almost half go completely unexplained despite post-mortem. We recently sequenced 35 arrhythmia-associated genes from 70 unexplained stillbirth cases. Our hypothesis was that deleterious mutations in channelopathy genes may have a functional effect in utero that may be pro-arrhythmic in the developing fetus. We observed four heterozygous, nonsynonymous variants in transient receptor potential melastatin 7 (TRPM7), a ubiquitously expressed ion channel known to regulate cardiac development and repolarization in mice. We used site-directed mutagenesis and single-cell patch-clamp to analyze the functional effect of the four stillbirth mutants on TRPM7 ion channel function in heterologous cells. We also used cardiomyocytes derived from human pluripotent stem cells to model the contribution of TRPM7 to action potential morphology. Our results show that two TRPM7 variants, p.G179V and p.T860M, lead to a marked reduction in ion channel conductance. This observation was underpinned by a lack of measurable TRPM7 protein expression, which in the case of p.T860M was due to rapid proteasomal degradation. We also report that human hiPSC-derived cardiomyocytes possess measurable TRPM7 currents; however, siRNA knockdown did not directly affect action potential morphology. TRPM7 variants found in the unexplained stillbirth population adversely affect ion channel function and this may precipitate fatal arrhythmia in utero

Sex Differences in the Morphology of RR-Matched T-waves

Evidence of sex-related differences in cardiac risk is emerging, but whether these reflect sex-related differences in ventricular electrophysiology remains unclear. Our aim was to quantify T-wave morphological differences between men and women across different leads and RR interval values. We analysed 12-lead ECG recordings from 23,962 participants in the UK Biobank without known cardiovascular disease, and subsequently clustered them into bins of RR interval. In each cluster, we derived a lead and sex-specific mean warped T-wave (MWT). Then, we quantified differences between MWT in men and women in time and amplitude using linear, d_{w} and d_{a}, and non-linear markers, d_{w}^{NL} and d_{a}^{NL}. Leads V3 and aVR showed the lowest differences between men and women (median d_{w}, d_{w}^{NL}, d_{a} and d_{a}^{NL} of 1.12 ms, 0.69 ms, 3.29 and 1.20, respectively), while V1 showed the largest (5.69 ms, 4.50 ms, 208.94 and 199.45, respectively). Sex-related differences in MWT increased with the RR interval (d_{w}, d_{w}^{NL}, d_{a} and d_{a}^{NL} ranging 1.44 - 5.89 ms, 1.23 - 3.97 ms, 8.58 - 28.38 and 1.53 - 4.41, respectively). These values compare to those found for morphological T-wave variations due to large changes in heart rate (5.66 ms, 2.35 ms, 57.61 and 9.51, respectively). These results indicate sex and lead should be considered when using T-wave morphologies for cardiovascular risk prediction

Evaluating the Impact of Physiological Variability in Genome-Wide Association Studies of Resting Heart Rate

Genome-wide association studies (GWAS) have discovered hundreds of genetic loci for resting heart rate (RHR). However, the impact of intra-individual variation in RHR on GWAS results is unclear. We evaluated this impact by analyzing two RHR recordings from N 61,000 subjects from UK Biobank. In addition, we modelled variations in RHR as independent white zero-mean Gaussian noise with a standard deviation of 0.5x, 1x, and 2x the standard deviation of the difference between the original RHR values (4,8, and 16 bpm, respectively). The two original RHR recordings were highly correlated (? =0.77), but results from the genetic analyses were s lightly different: the number of genome-wide significant (p < 5x10-8) variants at the locus with the strongest reported association (MYH6): n=39 vs. n=34; the p-value of the corresponding lead-variant, 3.6x10-24 vs. 2.1x10-19; and the estimated heritability 20.0% vs. 16.7%. Simulated data showed an inverse relationship between RHR variation and genetic association strength and heritability. Results formally demonstrate the impact of intra-individual RHR variability on the discovery of genetic variants in single-measurement studies

Prediction of Atrial and Ventricular Arrhythmias using Multiple Cardiovascular Risk Factor Polygenic Risk Scores.

BACKGROUND: Atrial fibrillation (AF) prediction improves by combining clinical scores with a polygenic risk score (PRS) for AF (AF-PRS), but there are limited studies of PRS for ventricular arrhythmia (VA) prediction. OBJECTIVE: We assessed the value of including multiple PRS for cardiovascular risk factors (CV-PRS) for incident AF and VA prediction. METHODS: We used 158,733 individuals of European ancestry from UK Biobank to build three models for AF: CHARGE-AF (AF1), AF1 + AF-PRS (AF2), AF2 + CV-PRS (AF3). Models for VA included sex and age (VA1), VA1 + coronary artery disease (CAD) PRS (CAD-PRS, VA2), and VA2 + CV-PRS (VA3), conducting separate analyses in subjects with and without ischemic heart disease (IHD). Performance was evaluated in individuals of European (N=158,733), African (N=7,200), South Asian (N=9,241) and East Asian (N=2,076) ancestry from UK Biobank. RESULTS: AF2 had a higher C-index than AF1 (0.762 versus 0.746, P<0.001), marginally improving to 0.765 for AF3 (P<0.001, including PRS for heart failure, electrocardiogram and cardiac magnetic resonance measures). In South Asians, AF2 C-index was higher than AF1 (P<0.001). For VA, the C-index for VA2 was greater than VA1 (0.692 versus 0.681, P<0.001) in Europeans, which was also observed in South Asians (P<0.001). VA3 improved prediction of VA in individuals with IHD. CONCLUSION: CV-PRS improved AF prediction compared to CHARGE-AF and AF-PRS. A CAD-PRS improved VA prediction, while CV-PRS contributed in IHD. AF- and CAD-PRS were transferable to individuals of South Asian ancestry. Our results inform of the use of CV-PRS for personalised screening

Ultra-Short Beat-to-Beat Repolarization Variability Predicts Cardiovascular Events in Individuals Without Cardiovascular Disease

The beat-to-beat variability of the QT interval (QTV) is thought to be a measure of sympathetic activity directed to the heart and it has predictive value in cardiac patients, but its predictive value in the general population is unclear. This study aimed to determine the association between ultra-short QTV from 15-second ECGs and future major adverse cardiovascular events (MACE) in a large cohort of middled aged individuals without previous cardiovascular disease. QTV was measured using the QTV index (QTVI), and the short-term QTV (STVQT) in n=55, 765 UK Biobank participants (54% female, 56.6±8.2 years old). The temporal variability of Q-Tpeak and Tpeak-Tend intervals was also assessed, and heart rate variability (RMSSD) was estimated for comparison. After a median follow-up of 12.5 years, n=2,542 (4.6%) MACE occurred. QTVI and STVQTV were associated with MACE and the association remained significant after adjusting for age, sex, bmi, diabetes, hypertension, smoking, betablockers, and, for STVQTV only, QT interval, resting heart rate, heart rate variability. QTVI showed the higher hazard ratio (1.10 (1.06, 1.15), p<0.01) and it was associated with MACE also when based on Q-Tpeak and Tpeak-Tend intervals. This study demonstrates for the first time that in the general population ultra-short repolarization variability from 15-sec ECG predicts MACE independently of traditional risk factors

Interaction between ECG and Genetic Markers of Coronary Artery Disease

Coronary artery disease (CAD) is the main contributor to cardiovascular mortality in developed countries, making accurate diagnosis of utmost importance. We developed risk scores to assess CAD risk in a population without known cardiovascular disease by combining ECG and a genetic risk score (GRS) for CAD. We analysed data in 52,260 individuals in the UK Biobank study. ECG indices included heart rate, PR, QRS, QT and T-peak-to-T-end intervals, while we built the GRS from publicly available genome-wide association results for CAD that were derived in an independent population. In a training set (N = 39,195), the indices with the strongest CAD prognostic impact were the PR and QT intervals, and the GRS. When combined together into a Multivariate model, both the ECG markers and the GRS were independently associated with CAD. In an independent test set (N = 13,065), we then built three risk scores based on (1) ECG markers, (2) genetic data, and (3) a combination of ECG and genetic data, respectively. The hazard ratio (95% confidence interval) for CAD comparing high versus low-risk individuals was 6.5 (5.1 - 8.3),8.4 (6.4 - 10.8) and 8.4 (6.5 - 10.8) for the three risk scores, respectively. In conclusion, the inclusion of genetic markers into risk scores with ECG markers independently contributes to CAD risk prediction in a large population of individuals without known cardiovascular disease

Clues from nearby galaxies to a better theory of cosmic evolution

The great advances in the network of cosmological tests show that the relativistic Big Bang theory is a good description of our expanding universe. But the properties of nearby galaxies that can be observed in greatest detail suggest a still better theory would more rapidly gather matter into galaxies and groups of galaxies. This happens in theoretical ideas now under discussion.Comment: published in Natur

The ric-8b protein (resistance to inhibitors of cholinesterase 8b) is key to preserving contractile function in the adult heart.

Resistance to inhibitors of cholinesterases (ric-8 proteins) are involved in modulating G-protein function, but little is known of their potential physiological importance in the heart. In the present study, we assessed the role of resistance to inhibitors of cholinesterase 8b (Ric-8b) in determining cardiac contractile function. We developed a murine model in which it was possible to conditionally delete ric-8b in cardiac tissue in the adult animal after the addition of tamoxifen. Deletion of ric-8b led to severely reduced contractility as measured using echocardiography days after administration of tamoxifen. Histological analysis of the ventricular tissue showed highly variable myocyte size, prominent fibrosis, and an increase in cellular apoptosis. RNA sequencing revealed transcriptional remodeling in response to cardiac ric-8b deletion involving the extracellular matrix and inflammation. Phosphoproteomic analysis revealed substantial downregulation of phosphopeptides related to myosin light chain 2. At the cellular level, the deletion of ric-8b led to loss of activation of the L-type calcium channel through the β-adrenergic pathways. Using fluorescence resonance energy transfer-based assays, we showed ric-8b protein selectively interacts with the stimulatory G-protein, Gαs. We explored if deletion of Gnas (the gene encoding Gαs) in cardiac tissue using a similar approach in the mouse led to an equivalent phenotype. The conditional deletion of the Gαs gene in the ventricle led to comparable effects on contractile function and cardiac histology. We conclude that ric-8b is essential to preserve cardiac contractile function likely through an interaction with the stimulatory G-protein and downstream phosphorylation of myosin light chain 2

Premature atrial and ventricular contractions detected on wearable-format electrocardiograms and prediction of cardiovascular events.

AIMS: Wearable devices are transforming the electrocardiogram (ECG) into a ubiquitous medical test. This study assesses the association between premature ventricular and atrial contractions (PVCs and PACs) detected on wearable-format ECGs (15 s single lead) and cardiovascular outcomes in individuals without cardiovascular disease (CVD). METHODS AND RESULTS: Premature atrial contractions and PVCs were identified in 15 s single-lead ECGs from N = 54 016 UK Biobank participants (median age, interquartile range, age 58, 50-63 years, 54% female). Cox regression models adjusted for traditional risk factors were used to determine associations with atrial fibrillation (AF), heart failure (HF), myocardial infarction (MI), stroke, life-threatening ventricular arrhythmias (LTVAs), and mortality over a period of 11.5 (11.4-11.7) years. The strongest associations were found between PVCs (prevalence 2.2%) and HF (hazard ratio, HR, 95% confidence interval = 2.09, 1.58-2.78) and between PACs (prevalence 1.9%) and AF (HR = 2.52, 2.11-3.01), with shorter prematurity further increasing risk. Premature ventricular contractions and PACs were also associated with LTVA (P < 0.05). Associations with MI, stroke, and mortality were significant only in unadjusted models. In a separate UK Biobank sub-study sample [UKB-2, N = 29,324, age 64, 58-60 years, 54% female, follow-up 3.5 (2.6-4.8) years] used for independent validation, after adjusting for risk factors, PACs were associated with AF (HR = 1.80, 1.12-2.89) and PVCs with HF (HR = 2.32, 1.28-4.22). CONCLUSION: In middle-aged individuals without CVD, premature contractions identified in 15 s single-lead ECGs are strongly associated with an increased risk of AF and HF. These data warrant further investigation to assess the role of wearable ECGs for early cardiovascular risk stratification

A Method to Minimise the Impact of ECG Marker Inaccuracies on the Spatial QRS-T angle: Evaluation on 1,512 Manually Annotated ECGs

© 2020 The Author(s) The spatial QRS-T angle (QRS-Ta) derived from the vectorcardiogram (VCG) is a strong risk predictor for ventricular arrhythmia and sudden cardiac death with potential use for mass screening. Accurate QRS-Ta estimation in the presence of ECG delineation errors is crucial for its deployment as a prognostic test. Our study assessed the effect of inaccurate QRS and T-wave marker placement on QRS-Ta estimation and proposes a robust method for its calculation. Reference QRS-Ta measurements were derived from 1,512 VCGs manually annotated by three expert reviewers. We systematically changed onset and offset timings of QRS and T-wave markers to simulate inaccurate placement. The QRS-Ta was recalculated using a standard approach and our proposed algorithm, which limits the impact of VCG marker inaccuracies by defining the vector origin as an interval preceding QRS-onset and redefines the beginning and end of QRS and T-wave loops. Using the standard approach, mean absolute errors (MAE) in peak QRS-Ta were >40% and sensitivity and precision in the detection of abnormality (>105°) were 15 ms. Using our proposed algorithm, MAE for peak QRS-Ta were reduced to 94% for inaccuracies up to ±15 ms. Similar results were obtained for mean QRS-Ta. In conclusion, inaccuracies of QRS and T-wave markers can significantly influence the QRS-Ta. Our proposed algorithm provides robust QRS-Ta measurements in the presence of inaccurate VCG annotation, enabling its use in large datasets