Exercise Capacity in Patients With Obstructive Hypertrophic Cardiomyopathy: SEQUOIA-HCM Baseline Characteristics and Study Design

Patients with obstructive hypertrophic cardiomyopathy (oHCM) have increased risk of arrhythmia, stroke, heart failure, and sudden death. Contemporary management of oHCM has decreased annual hospitalization and mortality rates, yet patients have worsening health-related quality of life due to impaired exercise capacity and persistent residual symptoms. Here we consider the design of clinical trials evaluating potential oHCM therapies in the context of SEQUOIA-HCM (Safety, Efficacy, and Quantitative Understanding of Obstruction Impact of Aficamten in HCM). This large, phase 3 trial is now fully enrolled (N = 282). Baseline characteristics reflect an ethnically diverse population with characteristics typical of patients encountered clinically with substantial functional and symptom burden. The study will assess the effect of aficamten vs placebo, in addition to standard-of-care medications, on functional capacity and symptoms over 24 weeks. Future clinical trials could model the approach in SEQUOIA-HCM to evaluate the effect of potential therapies on the burden of oHCM. (Safety, Efficacy, and Quantitative Understanding of Obstruction Impact of Aficamten in HCM [SEQUOIA-HCM]; NCT05186818).

Genome-Wide Analysis of Left Ventricular Maximum Wall Thickness in the UK Biobank Cohort Reveals a Shared Genetic Background With Hypertrophic Cardiomyopathy

BACKGROUND

Left ventricular maximum wall thickness (LVMWT) is an important biomarker of left ventricular hypertrophy and provides diagnostic and prognostic information in hypertrophic cardiomyopathy (HCM). Limited information is available on the genetic determinants of LVMWT.

METHODS

We performed a genome-wide association study of LVMWT measured from the cardiovascular magnetic resonance examinations of 42 176 European individuals. We evaluated the genetic relationship between LVMWT and HCM by performing pairwise analysis using the data from the Hypertrophic Cardiomyopathy Registry in which the controls were randomly selected from UK Biobank individuals not included in the cardiovascular magnetic resonance sub-study.

RESULTS

Twenty-one genetic loci were discovered at P<5×10-8. Several novel candidate genes were identified including PROX1, PXN, and PTK2, with known functional roles in myocardial growth and sarcomere organization. The LVMWT genetic risk score is predictive of HCM in the Hypertrophic Cardiomyopathy Registry (odds ratio per SD: 1.18 [95% CI, 1.13-1.23]) with pairwise analyses demonstrating a moderate genetic correlation (rg=0.53) and substantial loci overlap (19/21).

CONCLUSIONS

Our findings provide novel insights into the genetic underpinning of LVMWT and highlight its shared genetic background with HCM, supporting future endeavours to elucidate the genetic etiology of HCM.

Toward Replacing Late Gadolinium Enhancement With Artificial Intelligence Virtual Native Enhancement for Gadolinium-Free Cardiovascular Magnetic Resonance Tissue Characterization in Hypertrophic Cardiomyopathy

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging is the gold standard for noninvasive myocardial tissue characterization but requires intravenous contrast agent administration. It is highly desired to develop a contrast agent-free technology to replace LGE for faster and cheaper CMR scans.

METHODS

A CMR virtual native enhancement (VNE) imaging technology was developed using artificial intelligence. The deep learning model for generating VNE uses multiple streams of convolutional neural networks to exploit and enhance the existing signals in native T1 maps (pixel-wise maps of tissue T1 relaxation times) and cine imaging of cardiac structure and function, presenting them as LGE-equivalent images. The VNE generator was trained using generative adversarial networks. This technology was first developed on CMR datasets from the multicenter Hypertrophic Cardiomyopathy Registry, using hypertrophic cardiomyopathy as an exemplar. The datasets were randomized into 2 independent groups for deep learning training and testing. The test data of VNE and LGE were scored and contoured by experienced human operators to assess image quality, visuospatial agreement, and myocardial lesion burden quantification. Image quality was compared using a nonparametric Wilcoxon test. Intra- and interobserver agreement was analyzed using intraclass correlation coefficients (ICC). Lesion quantification by VNE and LGE were compared using linear regression and ICC.

RESULTS

A total of 1348 hypertrophic cardiomyopathy patients provided 4093 triplets of matched T1 maps, cines, and LGE datasets. After randomization and data quality control, 2695 datasets were used for VNE method development and 345 were used for independent testing. VNE had significantly better image quality than LGE, as assessed by 4 operators (n=345 datasets; P<0.001 [Wilcoxon test]). VNE revealed lesions characteristic of hypertrophic cardiomyopathy in high visuospatial agreement with LGE. In 121 patients (n=326 datasets), VNE correlated with LGE in detecting and quantifying both hyperintensity myocardial lesions (r=0.77-0.79; ICC=0.77-0.87; P<0.001) and intermediate-intensity lesions (r=0.70-0.76; ICC=0.82-0.85; P<0.001). The native CMR images (cine plus T1 map) required for VNE can be acquired within 15 minutes and producing a VNE image takes less than 1 second.

CONCLUSIONS

VNE is a new CMR technology that resembles conventional LGE but without the need for contrast administration. VNE achieved high agreement with LGE in the distribution and quantification of lesions, with significantly better image quality.

CalTrack: High-Throughput Automated Calcium Transient Analysis in Cardiomyocytes

[Figure: see text].

Myosin Sequestration Regulates Sarcomere Function, Cardiomyocyte Energetics, and Metabolism, Informing the Pathogenesis of Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is caused by pathogenic variants in sarcomere protein genes that evoke hypercontractility, poor relaxation, and increased energy consumption by the heart and increased patient risks for arrhythmias and heart failure. Recent studies show that pathogenic missense variants in myosin, the molecular motor of the sarcomere, are clustered in residues that participate in dynamic conformational states of sarcomere proteins. We hypothesized that these conformations are essential to adapt contractile output for energy conservation and that pathophysiology of HCM results from destabilization of these conformations.

METHODS

We assayed myosin ATP binding to define the proportion of myosins in the super relaxed state (SRX) conformation or the disordered relaxed state (DRX) conformation in healthy rodent and human hearts, at baseline and in response to reduced hemodynamic demands of hibernation or pathogenic HCM variants. To determine the relationships between myosin conformations, sarcomere function, and cell biology, we assessed contractility, relaxation, and cardiomyocyte morphology and metabolism, with and without an allosteric modulator of myosin ATPase activity. We then tested whether the positions of myosin variants of unknown clinical significance that were identified in patients with HCM, predicted functional consequences and associations with heart failure and arrhythmias.

RESULTS

Myosins undergo physiological shifts between the SRX conformation that maximizes energy conservation and the DRX conformation that enables cross-bridge formation with greater ATP consumption. Systemic hemodynamic requirements, pharmacological modulators of myosin, and pathogenic myosin missense mutations influenced the proportions of these conformations. Hibernation increased the proportion of myosins in the SRX conformation, whereas pathogenic variants destabilized these and increased the proportion of myosins in the DRX conformation, which enhanced cardiomyocyte contractility, but impaired relaxation and evoked hypertrophic remodeling with increased energetic stress. Using structural locations to stratify variants of unknown clinical significance, we showed that the variants that destabilized myosin conformations were associated with higher rates of heart failure and arrhythmias in patients with HCM.

CONCLUSIONS

Myosin conformations establish work-energy equipoise that is essential for life-long cellular homeostasis and heart function. Destabilization of myosin energy-conserving states promotes contractile abnormalities, morphological and metabolic remodeling, and adverse clinical outcomes in patients with HCM. Therapeutic restabilization corrects cellular contractile and metabolic phenotypes and may limit these adverse clinical outcomes in patients with HCM.

Analysis of 51 proposed hypertrophic cardiomyopathy genes from genome sequencing data in sarcomere negative cases has negligible diagnostic yield

PURPOSE

Increasing numbers of genes are being implicated in Mendelian disorders and incorporated into clinical test panels. However, lack of evidence supporting the gene-disease relationship can hinder interpretation. We explored the utility of testing 51 additional genes for hypertrophic cardiomyopathy (HCM), one of the most commonly tested Mendelian disorders.

METHODS

Using genome sequencing data from 240 sarcomere gene negative HCM cases and 6229 controls, we undertook case-control and individual variant analyses to assess 51 genes that have been proposed for HCM testing.

RESULTS

We found no evidence to suggest that rare variants in these genes are prevalent causes of HCM. One variant, in a single case, was categorized as likely to be pathogenic. Over 99% of variants were classified as a variant of uncertain significance (VUS) and 54% of cases had one or more VUS.

CONCLUSION

For almost all genes, the gene-disease relationship could not be validated and lack of evidence precluded variant interpretation. Thus, the incremental diagnostic yield of extending testing was negligible, and would, we propose, be outweighed by problems that arise with a high rate of uninterpretable findings. These findings highlight the need for rigorous, evidence-based selection of genes for clinical test panels.

Hypertrophic cardiomyopathy mutations in MYBPC3 dysregulate myosin

The mechanisms by which truncating mutations in MYBPC3 (encoding cardiac myosin-binding protein C; cMyBPC) or myosin missense mutations cause hypercontractility and poor relaxation in hypertrophic cardiomyopathy (HCM) are incompletely understood. Using genetic and biochemical approaches, we explored how depletion of cMyBPC altered sarcomere function. We demonstrated that stepwise loss of cMyBPC resulted in reciprocal augmentation of myosin contractility. Direct attenuation of myosin function, via a damaging missense variant (F764L) that causes dilated cardiomyopathy (DCM), normalized the increased contractility from cMyBPC depletion. Depletion of cMyBPC also altered dynamic myosin conformations during relaxation, enhancing the myosin state that enables ATP hydrolysis and thin filament interactions while reducing the super relaxed conformation associated with energy conservation. MYK-461, a pharmacologic inhibitor of myosin ATPase, rescued relaxation deficits and restored normal contractility in mouse and human cardiomyocytes with MYBPC3 mutations. These data define dosage-dependent effects of cMyBPC on myosin that occur across the cardiac cycle as the pathophysiologic mechanisms by which MYBPC3 truncations cause HCM. Therapeutic strategies to attenuate cMyBPC activity may rescue depressed cardiac contractility in patients with DCM, whereas inhibiting myosin by MYK-461 should benefit the substantial proportion of patients with HCM with MYBPC3 mutations.

Analysis of protein-coding genetic variation in 60,706 humans

Large-scale reference data sets of human genetic variation are critical for the medical and functional interpretation of DNA sequence changes. Here we describe the aggregation and analysis of high-quality exome (protein-coding region) DNA sequence data for 60,706 individuals of diverse ancestries generated as part of the Exome Aggregation Consortium (ExAC). This catalogue of human genetic diversity contains an average of one variant every eight bases of the exome, and provides direct evidence for the presence of widespread mutational recurrence. We have used this catalogue to calculate objective metrics of pathogenicity for sequence variants, and to identify genes subject to strong selection against various classes of mutation; identifying 3,230 genes with near-complete depletion of predicted protein-truncating variants, with 72% of these genes having no currently established human disease phenotype. Finally, we demonstrate that these data can be used for the efficient filtering of candidate disease-causing variants, and for the discovery of human 'knockout' variants in protein-coding genes.

Cardiac nitric oxide synthase 1 regulates basal and beta-adrenergic contractility in murine ventricular myocytes

BACKGROUND

Evidence indicates that myocardial NO production can modulate contractility, but the source of NO remains uncertain. Here, we investigated the role of a type 1 NO synthase isoform (NOS1), which has been recently localized to the cardiac sarcoplasmic reticulum, in the regulation of basal and beta-adrenergic myocardial contraction.

METHODS AND RESULTS

Contraction was assessed in left ventricular myocytes isolated from mice with NOS1 gene disruption (NOS1(-/-) mice) and their littermate controls (NOS1(+/+) mice) at 3 stimulation frequencies (1, 3, and 6 Hz) in basal conditions and during beta-adrenergic stimulation with isoproterenol (2 nmol/L). In addition, we examined the effects of acute specific inhibition of NOS1 with vinyl-L-N-5-(1-imino-3-butenyl)-L-ornithine (L-VNIO, 500 micromol/L). NOS1((-/-)) myocytes exhibited greater contraction at all frequencies (percent cell shortening at 6 Hz, 10.7+/-0.92% in NOS1(-/-) myocytes versus 7.21+/-0.8% in NOS1(+/+) myocytes; P<0.05) with a flat frequency-contraction relationship. Time to 50% relaxation was increased in NOS1(-/-) myocytes at all frequencies (at 6 Hz, 26.53+/-1.4 ms in NOS1(-/-) myocytes versus 21.27+/-1.3 ms in NOS1(+/+) myocytes; P<0.05). L-VNIO prolonged time to 50% relaxation at all frequencies (at 6 Hz, 21.28+/-1.7 ms in NOS1(+/+) myocytes versus 26.45+/-1.4 ms in NOS1(+/+)+L-VNIO myocytes; P<0.05) but did not significantly increase basal contraction. However, both NOS1(-/-) myocytes and NOS1(+/+) myocytes treated with L-VNIO showed a greatly enhanced contraction in response to beta-adrenergic stimulation (percent increase in contraction at 6 Hz, 25.2+/-10.8 in NOS1(+/+) myocytes, 68.2+/-11.2 in NOS1(-/-) myocytes, and 65.1+/-13.2 in NOS1(+/+)+L-VNIO myocytes; P<0.05).

CONCLUSIONS

NOS1 disruption enhances basal contraction and the inotropic response to beta-adrenergic stimulation in murine ventricular myocytes. These findings indicate that cardiac NOS1-derived NO plays a significant role in the autocrine regulation of myocardial contractility.

Genotype at a promoter polymorphism of the interleukin-6 gene is associated with baseline levels of plasma C-reactive protein

OBJECTIVE

Baseline concentrations of plasma C-reactive protein (CRP) are associated with coronary heart disease. Interleukin-6 (IL-6) regulates CRP gene expression; a promoter polymorphism (-174G/C) of the IL-6 gene has been shown to influence IL-6 transcription but the relationship between genotype at this polymorphism and circulating levels of inflammatory markers remains unclear. We hypothesised that plasma CRP would be a heritable phenotype that would be influenced by genotype at this polymorphism.

METHODS

We measured baseline plasma CRP and determined genotypes at the -174G/C polymorphism of the IL-6 gene in 588 members of 98 nuclear families. The heritability of plasma CRP and the association of plasma CRP with genotype were determined using variance components methods.

RESULTS

Baseline CRP levels were highly heritable (h(2)=0.39, P<0.0000001). Presence of the -174C allele was associated with higher baseline CRP levels, both in the whole population (P=0.01), and in the founders only (n=128, P=0.001). Family-based analyses confirmed the association (P=0.02) suggesting that it arises from chromosomal proximity or identity of the typed polymorphism with a genetic variant influencing baseline CRP levels.

CONCLUSIONS

Baseline plasma CRP is a significantly heritable cardiovascular risk factor. Levels are associated with genotype at the -174G/C polymorphism of the IL-6 gene.

Maintenance of Crohn's disease over 12 months: fixed versus flexible dosing regimen using budesonide controlled ileal release capsules

BACKGROUND

It may be possible to achieve more effective management of Crohn's Disease by introducing a flexible dosage regimen sensitive to patients' needs.

AIM

Comparison of the efficacy and tolerability of a fixed vs. flexible budesonide controlled ileal release treatment regimen for the prevention and management of relapse in Crohn's disease patients. Budesonide controlled ileal release is an oral formulation which delivers drug directly to disease sites in the ileum and ascending colon, by preventing more proximal release and absorption.

METHODS

A randomized, double-blind comparison of a fixed dose of budesonide controlled ileal release (6 mg o.m.) and a flexible dose of budesonide controlled ileal release (3, 6 or 9 mg o.m.) for 12 months, in 143 patients in remission from ileal or ileo-caecal Crohn's Disease.

RESULTS

Very low rates of clinical relapse in Crohn's disease were achieved with budesonide controlled ileal release 6 mg o.m. There was no significant difference between the treatment groups with respect to the survival estimate of percentage of treatment failures (flexible group 15%, fixed group 19%; P=0.61). The average consumed dose of budesonide was comparable in both groups (5.8 mg flexible, 6.0 mg fixed). Similar proportions of patients reported adverse events (flexible 100%, fixed 97%). There were 33 serious adverse events (flexible 19, fixed 14) and 13 withdrawals due to significant adverse events (flexible 9, fixed 4).

CONCLUSION

Maintenance treatment with budesonide controlled ileal release 6 mg o.m. is well-tolerated and is associated with low rates of clinical relapse in stable Crohn's disease over 12 months. Flexible dosing remains an option for individual patients, but this study has shown no advantage over a standard fixed dosing regimen.

Amplification of sequences from affected individuals

This unit describes methods for obtaining DNA sequences from an individual affected by a genetic disorder. Target sequences that may be present at very low copy number in patient samples are amplified by the polymerase chain reaction (PCR). The first Basic Protocol 1 describes harvesting of mRNA from peripheral lymphocytes, which can even be utilized for genes with tissue-specific patterns of expression. This technique has the advantage of ease of access to appropriate patient samples and also may provide a more efficient means of screening coding sequences than would analysis of individual exons. An alternate protocol describes modifications in PCR conditions that facilitate mutation analysis and sequencing. When the genomic sequence for a given candidate gene is known, the second Basic Protocol 2 may be used to obtain appropriate sequences for analysis of individual exons or noncoding regions of interest.

Detection of mutations by RNase cleavage

Ribonucleases can specifically recognize and cleave RNA at the site of sequence mismatches in RNA-DNA or RNA-RNA hybrids. The cleavage products are then characterized by gel electrophoresis. In this unit, a procedure is presented for RNase cleavage of (32)P-labeled riboprobes (transcribed from a cloned copy of the normal sequence) that have been annealed to amplified sequences of a candidate gene or cDNA obtained from affected individuals. A Support Protocol explains how to prepare riboprobes from a genomic or cDNA template obtained from a nonmutant individual. An alternate protocol describes cleavage of RNARNA hybrids using a nonisotopic RNase cleavage mutation assay. Sequential PCR and in vitro transcription steps generate sufficient quantities of duplex RNA targets so that the cleavage products can be detected on a gel by ethidium bromide staining. The unit also discusses the use of alternative ribonucleases for cleaving singlebase mismatches.

Familial Hypertrophic cardiomyopathy with Wolff-Parkinson-White syndrome maps to a locus on chromosome 7q3

We have mapped a disease locus for Wolff-Parkinson-White syndrome (WPW) and familial hypertrophic cardiomyopathy (FHC) segregating in a large kindred to chromosome 7 band q3. Although WPW syndrome and FHC have been observed in members of the same family in prior studies, the relationship between these two diseases has remained enigmatic. A large family with 25 surviving individuals who are affected by one or both of these conditions was studied. The disease locus is closely linked to loci D7S688, D7S505, and D7S483 (maximum two point LOD score at D7S505 was 7.80 at theta = 0). While four different FHC loci have been described this is the first locus that can be mutated to cause both WPW and/or FHC.

Assignment of the human a-tropomyosin gene TPM3 to 1q22-->q23 by fluorescence in situ hybridisation

The human tropomyosin 3 (TPM3) gene was previously localized to chromosome 1. The non-muscle isoform of the TPM3 gene product becomes fused to a gene product from the tyrosine kinase receptor gene (NTRK1), previously localized to 1q23-->q24, to generate an active oncogene. Two sequence tagged sites spanning three exons and two introns in the carboxy coding region of the gene were used to localize TPM3 to 1q22-->q23 by fluorescence in situ hybridization. This localization now places the NTRK1 and TPM3 genes in close proximity, so that a gene fusion rearrangement would not be cytologically detected. The 1q22-->q23 localization of TPM3 is within the NEM1 locus associated with autosomal dominant nemaline myopathy, making TPM3 a candidate for this disorder.

An evaluation of ribonuclease protection assays for the detection of beta-cardiac myosin heavy chain gene mutations

BACKGROUND

Ribonuclease (RNase) protection has been used to identify beta-cardiac myosin heavy chain (MHC) gene mutations that cause familial hypertrophic cardiomyopathy (FHC). Since more than 10 different mutations within this gene have been demonstrated to cause FHC in unrelated individuals, the genetic diagnosis of this condition will involve screening the beta-MHC gene. The accuracy with which RNase protection identifies such mutations is critical to defining the utility of this methodology in detecting mutations that cause FHC.

METHODS AND RESULTS

Twelve unrelated individuals with FHC were selected for further study because their beta-MHC genes had been screened for mutations by use of RNase protection, and no mutation was found. We performed linkage analysis of the families of these 12 probands using polymorphic short tandem repeats within the beta-MHC gene to determine whether FHC was genetically linked to the MHC locus on chromosome 14. FHC was not genetically linked to the MHC locus in 11 families whose beta-cardiac MHC gene did not contain mutations detectable by RNase protection.

CONCLUSIONS

We conclude that RNase protection is a sensitive method for screening for mutations within the beta-cardiac MHC gene. Further, mutations in the noncoding regions of the beta-MHC gene and mutations in the alpha-cardiac MHC gene are not a common cause of FHC. Negative RNase protection assays of affected individuals suggest that their FHC is due to mutations at other loci.