Paul J. R. Barton

Background and Aims: Dilated cardiomyopathy (DCM) is a genetically heterogeneous cause of heart failure and sudden cardiac death. Many patients remain without a molecular diagnosis. MAP3K7 encodes TAK1, a serine/threonine kinase important for cardiac homeostasis . MAP3K7 variants are an established cause of syndromic disease, including cardiospondylocarpofacial syndrome (CSCF), in which DCM has been occasionally reported. Here, we demonstrate that MAP3K7 variants can cause apparently isolated DCM, expanding the phenotypic spectrum of MAP3K7 -related disorders. Methods: We integrated four lines of genetic evidence: de novo variation, common variant association, familial segregation, and rare variant enrichment, alongside functional characterisation. Results: In 117 paediatric cardiomyopathy trios from the 100,000 Genomes Project, two probands harboured rare de novo MAP3K7 missense variants, significantly more than expected (Bonferroni-adjusted p=0.036). Independent GWAS implicated MAP3K7 as a susceptibility locus for adult DCM. Across global DCM cohorts, we identified families harbouring rare MAP3K7 variants, including one with segregation in nine affected relatives (p.(Tyr125Cys), estimated LOD = 2.7). Rare damaging non-truncating variants were enriched in DCM versus INTERVAL (OR 22, P=0.007) and gnomAD controls (OR 14, P=6.2×10⁻⁴), while truncating variants were associated with DCM in Genomics England and increased left ventricular volumes in UK Biobank. DCM-associated variants reduced TAK1 kinase activity, supporting a loss-of-function mechanism consistent with CSCF-associated alleles. Conclusion: Multiple independent lines of evidence establish an association between MAP3K7 loss of function variants and DCM. Several affected individuals lacked overt syndromic features, demonstrating that MAP3K7 -related disease may present as apparently isolated DCM across the lifespan and supporting inclusion of MAP3K7 in DCM diagnostic pipelines. GRAPHICAL Key Question: Do MAP3K7 variants cause isolated dilated cardiomyopathy?: MAP3K7 variants are known to cause rare syndromic disease, including cardiospondylocarpofacial syndrome (CSCF). Some patients with CSCF develop dilated cardiomyopathy (DCM), however we do not know whether MAP3K7 variants cause primary or isolated DCM without overt syndromic disease. Key Finding: We present multiple orthogonal data sources supporting an association between MAP3K7 loss-of-function variants and DCM. The collective evidence for this gene-disease association encompasses paediatric trio de novo discovery, GWAS, familial segregation, rare variant case-control analysis and variant categorisation in vitro . Strong segregation evidence was obtained for p.(Tyr125Cys), with nine clinically affected genotype-positive individuals in one pedigree (estimated LOD score 2.7). Further, p.(Cys266del) was observed in three affected individuals in one family and a de novo paediatric case. Take-Home Message: Loss-of-function variants in MAP3K7 are associated with DCM and several affected individuals lack overt syndromic features. MAP3K7 -related disease may present as apparently isolated DCM across the lifespan. These findings support the incorporation of MAP3K7 testing into DCM diagnostic pipelines.

The alternative calcineurin A variant CnAβ1 has a unique C-terminal domain that provides it with distinct subcellular localization and mechanism of action different from other calcineurin isoforms. Here, we used mice lacking CnAβ1’s C-terminal domain (CnAβ1 ^Δi12 ) to show that the absence of this specific isoform strongly reprograms metabolism. CnAβ1 ^Δi12 mice on a high-fat diet showed reduced body weight, white adipose tissue (WAT) mass, and circulating triglycerides, together with enhanced insulin sensitivity. In brown adipose tissue (BAT), CnAβ1 deficiency increased mitochondrial content and upregulated fatty acid oxidation and thermogenic proteins, improving cold resistance. Conversely, under starvation, CnAβ1 ^Δi12 mice experienced rapid fat depletion and hypothermia. Importantly, BAT-specific FoxO1 knockout in CnAβ1 ^Δi12 mice reduced catabolism-related gene expression and partially reversed the metabolic phenotypes, increasing body weight and WAT mass. Our findings reveal a relevant role for CnAβ1 in orchestrating BAT metabolism, highlighting its potential as a therapeutic target for obesity and metabolic syndrome.

Hypertrophic cardiomyopathy (HCM) is an important cause of morbidity and mortality with both monogenic and polygenic components. Here, we report results from a large genome-wide association study and multitrait analysis including 5,900 HCM cases, 68,359 controls and 36,083 UK Biobank participants with cardiac magnetic resonance imaging. We identified 70 loci (50 novel) associated with HCM and 62 loci (20 novel) associated with relevant left ventricular traits. Among the prioritized genes in the HCM loci, we identify a novel HCM disease gene, SVIL , which encodes the actin-binding protein supervillin, showing that rare truncating SVIL variants confer a roughly tenfold increased risk of HCM. Mendelian randomization analyses support a causal role of increased left ventricular contractility in both obstructive and nonobstructive forms of HCM, suggesting common disease mechanisms and anticipating shared response to therapy. Taken together, these findings increase our understanding of the genetic basis of HCM, with potential implications for disease management.

Hypertrophic cardiomyopathy (HCM) is an important cause of morbidity and mortality, with pathogenic variants found in about a third of cases. Large-scale genome-wide association studies (GWAS) demonstrate that common genetic variation contributes to HCM risk. Here we derive polygenic scores (PGS) from HCM GWAS and genetically correlated traits and test their performance in the UK Biobank, 100,000 Genomes Project, and clinical cohorts. We show that higher PGS significantly increases the risk of HCM in the general population, particularly among pathogenic variant carriers, where HCM penetrance differs 10-fold between those in the highest and lowest PGS quintiles. Among relatives of HCM probands, PGS stratifies risks of developing HCM and adverse outcomes. Finally, among HCM cases, PGS strongly predicts the risk of adverse outcomes and death. These findings support the broad utility of PGS across clinical settings, enabling tailored screening and surveillance and stratification of risk of adverse outcomes.

Gene panels represent a widely used strategy for genetic testing in a vast range of Mendelian disorders. While this approach aids reliable bioinformatic detection of short coding variants, it fails to detect most larger variants. Recent studies have recommended the adoption of pangenomes to augment detection of large variants from targeted sequencing, potentially providing diagnostic laboratories with the possibility to streamline diagnostic work-ups and reduce costs. Here, we analyze a large-scale cohort comprising 1,952 cardiomyopathy cases and 1,805 technically matched controls and show that a pangenome-based workflow, GRAF, conjugates higher precision and recall (F1 score 0.86) compared with conventional orthogonal methods (F1 0-0.57) in detecting potentially pathogenic ≥20bp variants from short-read panel data. Our results indicate that pangenome-based workflows aid precise and cost-effective detection of large variants from targeted sequencing data in the clinical context. This will be particularly relevant for conditions in which these variants explain a high proportion of the disease burden.

Dilated cardiomyopathy (DCM) is a leading cause of heart failure and cardiac transplantation. We report a genome-wide association study and multi-trait analysis of DCM (14,256 cases) and three left ventricular traits (36,203 UK Biobank participants). We identified 80 genomic risk loci and prioritized 62 putative effector genes, including several with rare variant DCM associations (MAP3K7, NEDD4L and SSPN). Using single-nucleus transcriptomics, we identify cellular states, biological pathways, and intracellular communications that drive pathogenesis. We demonstrate that polygenic scores predict DCM in the general population and modify penetrance in carriers of rare DCM variants. Our findings may inform the design of genetic testing strategies that incorporate polygenic background. They also provide insights into the molecular etiology of DCM that may facilitate the development of targeted therapeutics.

Background: Interleukin 11 (IL11) was initially thought important for platelet production, which led to recombinant IL11 being developed as a drug to treat thrombocytopenia. IL11 was later found to be redundant for haematopoiesis and its use in patients is associated with unexplained cardiac side effects. Here we identify previously unappreciated and direct cardiomyocyte toxicities associated with IL11 therapy. Methods: We injected recombinant mouse lL11 (rmIL11) into mice and studied its molecular effects in the heart using immunoblotting, qRT-PCR, bulk RNA-seq, single nuclei RNA-seq (snRNA-seq) and ATAC-seq. The physiological impact of IL11 was assessed by echocardiography in vivo and using cardiomyocyte contractility assays in vitro . To determine the activity of IL11 specifically in cardiomyocytes we made two cardiomyocyte-specific Il11ra1 knockout mouse models using either AAV9-mediated and Tnnt2 -restricted (vCMKO) or Myh6 (m6CMKO) Cre expression and an Il11ra1 floxed mouse strain. In pharmacologic studies, we studied the effects of JAK/STAT inhibition on rmIL11-induced cardiac toxicities. Results: Injection of rmIL11 caused acute and dose-dependent impairment of left ventricular ejection fraction (saline (2 µL/kg), 60.4%±3.1; rmIL11 (200 mcg/kg), 31.6%±2.0; pAnkrd1 , Ankrd23 , Xirp2 ), activator protein-1 (AP-1) transcription factor genes and Nppb in the cardiomyocyte compartment. Following rmIL11 injection, ATAC-seq identified epigenetic enrichment of the Ankrd1 and Nppb genes and stress-responsive, AP-1 transcription factor binding sites. Cardiomyocyte-specific effects were examined in vCMKO and m6CMKO mice, which were both protected from rmIL11-induced left ventricular impairment and molecular pathobiologies. In mechanistic studies, inhibition of JAK/STAT signalling with either ruxolitinib or tofacitinib prevented rmIL11-induced cardiac dysfunction. Conclusions: Injection of IL11 directly activates JAK/STAT3 in cardiomyocytes to cause acute heart failure. Our data overturn the earlier assumption that IL11 is cardioprotective and explain the serious cardiac side effects associated with IL11 therapy, which questions its continued use in patients. Clinical Perspective: What is new?: Injection of IL11 to mice causes acute and dose-dependent left ventricular impairment IL11 activates JAK/STAT3 in cardiomyocytes to cause cell stress, inflammation and impaired calcium handling These data identify, for the first time, that IL11 is directly toxic in cardiomyocytes, overturning the earlier literature that suggested the opposite What are the clinical implications?: Recombinant human IL11 (rhIL11) is used as a drug to increase platelets in patients with thrombocytopenia but this has severe and unexplained cardiac side effects We show that IL11 injection causes cardiomyocyte dysfunction and heart failure, which explains its cardiac toxicities that were previously thought non-specific These findings have immediate translational implications as they question the continued use of rhIL11 in patients around the world