Biology subjects

Semsarian, C.

Publications and source records attributed to Semsarian, C..

6 recordsLinked to original sources

bioRxiv2024

An ALPK3 truncation variant causing autosomal dominant hypertrophic cardiomyopathy is partially rescued by mavacamten

The ALPK3 gene encodes alpha-protein kinase 3, a cardiac pseudo-kinase of unknown function. Heterozygous truncating variants (ALPK3tv) can cause dominant adult-onset Hypertrophic Cardiomyopathy (HCM). Here we confirm an excess of ALPK3tv in sarcomere-gene negative HCM patients. Moreover, we generated a novel knock-in mouse model carrying an ALPK3tv (K201X). Homozygous animals displayed hypertrophy and systolic dysfunction. Heterozygous animals demonstrated no obvious baseline; however, they had an aggravated hypertrophic response upon chronic adrenergic challenge. Isolated cardiomyocytes from heterozygous and homozygous mice showed reduced basal sarcomere length with prolonged relaxation, whilst calcium transients showed increased diastolic calcium levels and prolonged re-uptake. We also observed reduced fractional shortening. Protein kinase A-mediated phosphorylation, including that of cardiac troponin I, was significantly decreased. In agreement with the cellular HCM phenotype, reduced ratios of myosin heads in the super-relaxed state were measured. Contractile and calcium handling defects were partly corrected by treatment with mavacamten, a novel myosin inhibitor. For the first time with a non-sarcomere HCM variant, we have demonstrated hallmark changes in cardiac contractility and calcium handling, some resembling sarcomere-positive HCM, while others are distinct and DCM-like. Mavacamten is able to partially rescue the cellular phenotype, hence could be beneficial to HCM patients with ALPK3tv.

genetics↗

bioRxiv2023

Atenolol reduces cardiac-mediated mortality in a genetic mouse model of sudden unexpected death in epilepsy

Sudden Unexpected Death in Epilepsy (SUDEP) is the leading cause of premature mortality in epilepsy. Genetic cardiac risk factors, including loss-of-function KCNH2 variants, have been linked to SUDEP. We hypothesised that seizures and LQTS interact to increase SUDEP risk. To investigate this, we crossed Kcnh2+/- and Gabrg2R43Q/+ mice that model LQTS and genetic epilepsy, respectively. Electrocorticography and electrocardiogram confirmed that Kcnh2+/- mice had a LQTS phenotype, while Gabrg2R43Q/+ mice displayed spontaneous seizures. Double mutant mice (Gabrg2R43Q/+/Kcnh2+/-) had both seizure and LQTS phenotypes that were indistinguishable from the respective single mutant mice. Survival analysis revealed that Gabrg2R43Q/+/Kcnh2+/- mice experienced a disproportionate higher rate of seizure-related death. Long-term oral administration of atenolol, a cardiac-selective {beta}-blocker, significantly improved survival in the Gabrg2R43Q/+/Kcnh2+/- mice. An additional mouse model, Hcn1M294L/+/Kcnh2+/-, based on a HCN1 developmental epileptic encephalopathy variant, also experienced a disproportionately higher rate of premature death that was rescued by atenolol. Kcnh2+/- mice also spent more time in ventricular arrhythmia during proconvulsant-induced seizures. Overall, the data implicates cardiac and loss-of-function KCNH2 variants as an important risk factor, and the potential repurposing of {beta}- blockers as a prevention strategy, for SUDEP in a subset of epilepsy patients.

neuroscience↗

bioRxiv2023

Slow conduction and spatial dispersion of repolarization are intrinsic properties of cardiomyocyte electrophysiology that contribute to proarrhythmia in an iPSC model of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited heart muscle disease; characterised by left ventricular wall thickening, cardiomyocyte disarray, and fibrosis, and is associated with arrhythmias, heart failure and sudden death. However, it is unclear to what extent the electrophysiological disturbances that lead to sudden death occur secondary to the structural changes in the myocardium, or as a result of intrinsic properties of the HCM cardiomyocyte. In this study, we used an induced pluripotent stem cell model of the Arg403Gln variant in myosin heavy chain 7 (MYH7) to study tissue level electrophysiological properties of HCM cardiomyocytes. For the first time, we show significant slowing of conduction velocity and an increase in local spatial dispersion of repolarisation - both well-established substrates for arrhythmia - in monolayers of HCM cardiomyocytes. Analysis of rhythmonome protein expression in R403Q cardiomyocytes revealed dramatically reduced connexin-43, sodium channels, and inward rectifier channels - a three-way hit that combines to reduce electrotonic coupling between HCM cardiomyocytes and slow cardiac conduction. Our data therefore represent a novel, biophysical basis for arrhythmia in HCM, that is intrinsic to cardiomyocyte electrophysiology. Later in the progression of the disease, these proarrhythmic electrical phenotypes may be accentuated by fibrosis and myocyte disarray to contribute to sudden death in HCM patients.

physiology↗

bioRxiv2021

Loss-of-function variants in the cardiac Kv11.1 channel as a genetic biomarker for SUDEP

ObjectiveTo compare the frequency and impact on channel function of KCNH2 variants in SUDEP patients with epilepsy controls comprising patients older than 50 years, a group with low SUDEP risk, and establish loss-of-function KCNH2 variants as predictive biomarkers of SUDEP risk. MethodsWe searched for KCNH2 variants with a minor allele frequency of < 5%. Functional analysis in Xenopus laevis oocytes was performed for all KCNH2 variants identified. ResultsKCNH2 variants were found in 11.1% (10/90) of SUDEP individuals compared to 6.0% (20/332) of epilepsy controls (p = 0.11). Loss-of-function KCNH2 variants, defined as causing > 20% reduction in maximal amplitude, were observed in 8.9% (8/90) SUDEP patients compared to 3.3% (11/332) epilepsy controls suggesting about three-fold enrichment (nominal p = 0.04). KCNH2 variants that did not change channel function occurred at a similar frequency in SUDEP (2.2%; 2/90) and epilepsy control (2.7%; 9/332) cohorts (p > 0.99). Rare KCNH2 variants (< 1% allele frequency) associated with greater loss of function and an [~]11-fold enrichment in the SUDEP cohort (nominal p = 0.03). In silico tools were unable to predict the impact of a variant on function highlighting the need for electrophysiological analysis. ConclusionsThese data show that loss-of-function KCNH2 variants are enriched in SUDEP patients and suggest that cardiac mechanisms contribute to SUDEP risk. We propose that genetic screening in combination with functional analysis can identify loss-of-function KCNH2 variants that could act as biomarkers of an individuals SUDEP risk.

neuroscience↗

bioRxiv2020

Computational prediction of protein subdomain stability in MYBPC3 enables clinical risk stratification in hypertrophic cardiomyopathy and enhances variant interpretation.

PurposeVariants in MYBPC3 causing loss-of-function are the most common cause of HCM. However, a substantial number of patients carry missense variants of uncertain significance (VUS) in MYBPC3. We hypothesize that a structural-based algorithm, STRUM, which estimates the effect of missense variants on protein folding, will improve clinical risk stratification of patients with HCM and a MYBPC3 VUS. MethodsAmong 7,963 patients in the multi-center Sarcomeric Human Cardiomyopathy Registry, 120 unique missense VUSs in MYBPC3 were identified. Variants were evaluated for their effect on subdomain folding and a stratified time-to-event analysis for an overall composite endpoint (first occurrence of ventricular arrhythmia, heart failure, all-cause mortality, atrial fibrillation, and stroke) was performed for patients with HCM and a MYBPC3 missense VUS. ResultsWe demonstrated that patients carrying a MYBPC3 VUS predicted to cause subdomain misfolding (STRUM +, {Delta}{Delta}G [≤]-1.2 kcal/mol) exhibited a higher rate of adverse events compared to those with a STRUM-VUS (Hazard Ratio=2.29, P=0.0282). In silico saturation mutagenesis of MYBPC3 identified 4,943/23,427 (21%) missense variants that were predicted to cause subdomain misfolding. ConclusionsSTRUM enables clinical risk stratification of patients with HCM and a MYBPC3 VUS and has the capacity to improve prognostic predictions and clinical decision making.

genetics↗

bioRxiv2020

Disease-specific variant pathogenicity prediction significantly improves variant interpretation in inherited cardiac conditions

BackgroundAccurate discrimination of benign and pathogenic rare variation remains a priority for clinical genome interpretation. State-of-the-art machine learning tools are useful for genome-wide variant prioritisation but remain imprecise. Since the relationship between molecular consequence and likelihood of pathogenicity varies between genes with distinct molecular mechanisms, we hypothesised that a disease-specific classifier may outperform existing genome-wide tools. MethodsWe present a novel disease-specific variant classification tool, CardioBoost, that estimates the probability of pathogenicity for rare missense variants in inherited cardiomyopathies and arrhythmias, trained with variants of known clinical effect. To benchmark against state-of-the-art genome-wide pathogenicity classification tools, we assessed classification of hold-out test variants using both overall performance metrics, and metrics of high-confidence (>90%) classifications relevant to variant interpretation. We further evaluated the prioritisation of variants associated with disease and patient clinical outcomes, providing validations that are robust to potential mis-classification in gold-standard reference datasets. ResultsCardioBoost has higher discriminating power than published genome-wide variant classification tools in distinguishing between pathogenic and benign variants based on overall classification performance measures with the highest area under the Precision-Recall Curve as 91% for cardiomyopathies and as 96% for inherited arrhythmias. When assessed at high-confidence (>90%) classification thresholds, prediction accuracy is improved by at least 120% over existing tools for both cardiomyopathies and arrhythmias, with significantly improved sensitivity and specificity. Finally, CardioBoost improves prioritisation of variants significantly associated with disease, and stratifies survival of patients with cardiomyopathies, confirming biologically relevant variant classification. ConclusionsWe demonstrate that a disease-specific variant pathogenicity prediction tool outperforms state-of-the-art genome-wide tools for the classification of rare missense variants of uncertain significance for inherited cardiac conditions. To facilitate evaluation of CardioBoost, we provide pre-computed pathogenicity scores for all possible rare missense variants in genes associated with cardiomyopathies and arrhythmias (https://www.cardiodb.org/cardioboost/). Our results also highlight the need to develop and evaluate variant classification tools focused on specific diseases and clinical application contexts. Our proposed model for assessing variants in known disease genes, and the use of application-specific evaluations, is broadly applicable to improve variant interpretation across a wide range of Mendelian diseases.

genetics↗