Hypertrophic Cardiomyopathy Without Hypertrophy

Cardiac hypertrophy and arrhythmia in mice induced by a mutation in ryanodine receptor 2

Hypertrophic cardiomyopathy (HCM) is triggered mainly by mutations in genes encoding sarcomeric proteins, but a significant proportion of patients lack a genetic diagnosis. We identified a novel mutation in the ryanodine receptor 2, RyR2-P1124L, in a patient from a genotype-negative HCM cohort. The aim of this study was to determine whether RyR2-P1124L triggers functional and structural alterations in isolated RyR2 channels and whole hearts. We found that P1124L induces significant conformational changes in the SPRY2 domain of RyR2. Recombinant RyR2-P1124L channels displayed a cytosolic loss-of-function phenotype, which contrasted with a higher sensitivity to luminal [Ca2+], indicating a luminal gain-of-function. Homozygous mice for RyR2-P1124L showed mild cardiac hypertrophy, similar to the human patient. This phenotype, evident at 1 yr of age, was accompanied by an increase in the expression of calmodulin (CaM). P1124L mice also showed higher susceptibility to arrhythmia at 8 mo of age, before the onset of hypertrophy. RyR2-P1124L has a distinct cytosolic loss-of-function and a luminal gain-of-function phenotype. This bifunctionally-divergent behavior triggers arrhythmias and structural cardiac remodeling, and involves overexpression of calmodulin as a potential hypertrophic mediator. This study is relevant to continue elucidating the possible causes of genotype-negative HCM and the role of RyR2 in cardiac hypertrophy.

Biomarkers of cardiovascular stress and fibrosis in preclinical hypertrophic cardiomyopathy

Objective

Sarcomeric gene mutation carriers without overt left ventricular hypertrophy (G+/LVH-) can harbour subclinical changes in cardiovascular structure and function that precede the development of hypertrophic cardiomyopathy (HCM). We sought to investigate if circulating biomarkers of cardiovascular stress and collagen metabolism among G+/LVH- individuals, measured at rest and following exercise provocation, yield further insights into the underlying biology of HCM.

Methods

We studied 76 individuals with overt HCM, 50 G+/LVH- individuals and 41 genotype-negative related controls enrolled in a cross-sectional, multicentre observational study (HCMNet). Biomarkers of cardiac stress (N-terminal pro-B-type natriuretic peptide, NT-proBNP; high-sensitivity troponin I, hsTnI; soluble ST2) and fibrosis (carboxy-terminal propeptide of procollagen type I; C-terminal telopeptide of type I collagen; galectin-3; periostin) were measured.

Results

Individuals with overt HCM had elevated NT-proBNP and hsTnI compared with G+/LVH- subjects and controls at rest, along with an exaggerated increase in NT-proBNP and hsTnI in response to exercise. We found no detectable differences in resting or exercise-provoked biomarker profiles of cardiovascular stress and fibrosis among G+/LVH- individuals compared with healthy controls despite subtle echocardiographic differences in cardiac structure and function.

Conclusion

Dynamic exercise testing exaggerated resting differences in natriuretic peptides and troponin elevations among individuals with overt HCM. In contrast, we found no differences in biomarker profiles of cardiovascular stress and fibrosis among G+/LVH- individuals compared with controls even after maximal exercise provocation. Our findings highlight the need for continued investigation into early phenotypes of sarcomeric gene mutations and the evolution of HCM.

Diastolic Dysfunction of Hypertrophic Cardiomyopathy Genotype-Positive Subjects Without Hypertrophy Is Detected by Tissue Doppler Imaging: A Systematic Review and Meta-analysis

OBJECTIVES

To evaluate whether diastolic dysfunction derived by tissue Doppler imaging (TDI) would be an earlier manifestation in genotype-positive hypertrophic cardiomyopathy (HCM) subjects without left ventricular hypertrophy (LVH).

METHODS

We systematically searched Pubmed, Medline, and Web of Science with an upper date limit of June 2016 for studies evaluating the diastolic function of HCM genotype-positive subjects without hypertrophy (G+/LVH-). Based on the inclusion criteria, eligible studies were selected. The quality of selected studies was assessed by the Newcastle-Ottawa Scale before being included in the meta-analysis. The statistic data such as weighted mean difference (WMD) and 95% confidence interval (CI) were calculated by Stata 12.0 software.

RESULTS

Seventeen studies were included in the systematic review, and 12 were finally involved in the meta-analysis. The G+/LVH- subjects showed decreased Ea derived by TDI on both the interventricular septum (WMD [95% CI] = -1.822 [-3.104, -0.541]) and lateral wall (WMD [95% CI] = -2.269 [-3.820, -0.719]), and increased E/Ea on both interventricular septum (WMD [95% CI] = 1.363 [0.552, 2.174]) and lateral (WMD [95% CI] = 1.339 [0.386, 2.293]) wall.

CONCLUSIONS

Tissue Doppler imaging-derived diastolic dysfunction can be found in HCM genotype-positive subjects without hypertrophy.

The Muscle-Bound Heart

Hypertrophic cardiomyopathy (HCM) is a familial cardiac disease manifested in a wide phenotype and diverse genotype and, thus, presenting unpredictable risks mainly on young adults. Extensive studies are being conducted to categorize patients and link phenotype with genotype for a better management and control of the disease with all its complications. Because the full mechanisms behind HCM are still not revealed, therapeutics are not definitive. Further research is to be conducted for the generation of a complete picture and directed therapy for HCM.

The influence of clinical and genetic factors on left ventricular wall thickness in Ragdoll cats

OBJECTIVES

To investigate the effect of various genetic and environmental modifiers on left ventricular (LV) wall thickness in a cohort of cats genotyped for the myosin binding protein C3 mutation (MYBPC3).

ANIMALS

Sixty-four Ragdoll cats.

METHODS

All cats were screened for HCM with echocardiography and genotyping for the HCM-associated MYBPC3:R820W mutation. Cats were also genotyped for previously identified variant polymorphisms of the angiotensin-converting enzyme (ACE) and cardiac beta-adrenergic receptor (ADRB1) genes. Plasma N-terminal pro-B-type natriuretic peptide and cardiac troponin I were also measured. Associations were evaluated between genotype (MYBPC3 negative/positive, and ACE and ADRB1 negative/heterozygous/homozygous), patient factors (body weight, age and sex) and echocardiographic measurements of LV wall thickness.

RESULTS

Male cats had greater maximum wall thickness (LVmax; 5.8 mm, IQR 5.1-6.4 mm) than females (4.7 mm, IQR 4.4-5.3 mm, p = 0.002). Body weight positively correlated with LVmax (ρ = 0.604, p < 0.001). The MYBPC3:R820W-positive cats had a greater LVmax (5.44 mm, IQR 4.83-6.28 mm) than the negative cats (4.76 mm, IQR 4.36-5.32 mm, p = 0.001). Also, the ACE polymorphism genotype was associated with LVmax: the homozygous cats (5.37 mm, IQR 5.14-6.4 mm) had greater LVmax than the heterozygous cats (4.73 mm, IQR 4.41-5.55 mm, p = 0.014). Only the MYBPC3 genotype and body weight were independently associated with wall thickness in multivariable analysis.

CONCLUSIONS

This study provides evidence that the MYBPC3:R820W mutation is independently associated with LV wall thickness in Ragdoll cats. Body weight is also independently associated with maximum LV wall thickness, but is not currently accounted for in HCM screening. In addition, other genetic modifiers may be associated with variation in LV wall thickness in Ragdolls.

Targets for therapy in sarcomeric cardiomyopathies

To date, no compounds or interventions exist that treat or prevent sarcomeric cardiomyopathies. Established therapies currently improve the outcome, but novel therapies may be able to more fundamentally affect the disease process and course. Investigations of the pathomechanisms are generating molecular insights that can be useful for the design of novel specific drugs suitable for clinical use. As perturbations in the heart are stage-specific, proper timing of drug treatment is essential to prevent initiation and progression of cardiac disease in mutation carrier individuals. In this review, we emphasize potential novel therapies which may prevent, delay, or even reverse hypertrophic cardiomyopathy caused by sarcomeric gene mutations. These include corrections of genetic defects, altered sarcomere function, perturbations in intracellular ion homeostasis, and impaired myocardial energetics.

Using genetic testing to guide therapeutic decisions in cardiomyopathy

OPINION STATEMENT

Genetic analysis of human cardiomyopathy has rapidly transitioned from a strictly research endeavor to a diagnostic tool readily available to clinicians across the globe. In contemporary practice, genetic testing improves the efficiency of family evaluations and clarifies the etiology of ambiguous clinical presentations. The great promise of genetic diagnosis is to enable preventative therapies for individuals at high risk of future disease development, a strategy that is under active clinical investigation. However, in the present and future, careful interpretation of DNA sequence variation is critical, and can be ensured by referral to a specialized cardiovascular genetics clinic.

Early results of sarcomeric gene screening from the Egyptian National BA-HCM Program

The present study comprised sarcomeric genotyping of the three most commonly involved sarcomeric genes: MYBPC3, MYH7, and TNNT2 in 192 unrelated Egyptian hypertrophic cardiomyopathy (HCM) index patients. Mutations were detected in 40 % of cases. Presence of positive family history was significantly (p = 0.002) associated with a higher genetic positive yield (49/78, 62.8 %). The majority of the detected mutations in the three sarcomeric genes were novel (40/62, 65 %) and mostly private (47/62, 77 %). Single nucleotide substitution was the most frequently detected mutation type (51/62, 82 %). Over three quarters of these substitutions (21/27, 78 %) involved CpG dinucleotide sites and resulted from C > T or G > A transition in the three analyzed genes, highlighting the significance of CpG high mutability within the sarcomeric genes examined. This study could aid in global comparative studies in different ethnic populations and constitutes an important step in the evolution of the integrated clinical, translational, and basic science HCM program.

Diastolic abnormalities in normal phenotype hypertrophic cardiomyopathy gene carriers: a study using speckle tracking echocardiography

BACKGROUND

Tissue Doppler imaging (TDI) of the mitral annulus has been proposed as an alternative for the identification of hypertrophic cardiomyopathy (HCM) genetically affected subjects without left ventricular hypertrophy (G+/LVH-). Unfortunately, conflicting results have been described in the literature, potentially caused by the angle-dependency of TDI. This study sought to assess abnormalities in mitral annular velocities in G+/LVH- subjects as detected by speckle tracking echocardiography (STE).

METHODS

The study population consisted of 23 consecutive genotyped family members without major or minor criteria for the diagnosis of HCM (mean age 37 ± 13 years, 9 men) and 23 healthy volunteers (age 38 ± 12 years, 12 men) who prospectively underwent STE.

RESULTS

There were no significant differences in global peak systolic annular velocity (7.4 ± 1.2 vs. 7.1 ± 1.0 cm/sec) and early diastolic annular velocity (10.2 ± 2.5 vs. 11.3 ± 2.2 cm/sec) between G+/LVH- and control subjects. Global peak late diastolic annular velocity was higher in G+/LVH- subjects (8.1 ± 1.7 vs. 5.7 ± 1.1 cm/sec, P < 0.001). Regionally, this difference was seen in all 6 studied LV walls.

CONCLUSIONS

This STE study confirms our previous TDI observations on increased peak late diastolic annular velocities in G+/LVH- subjects. Because of the complete overlap in early diastolic annular velocities this parameter cannot be used in the genotypes we studied to differentiate genotype (+) from genotype (-) individuals.

MRI of nonischemic cardiomyopathy

OBJECTIVE

The purpose of this article is to present current clinical and research issues in MRI evaluation of nonischemic cardiomyopathy, a diverse set of diseases, many of which have a genetic basis.

CONCLUSION

Cardiac cine MRI along with delayed myocardial enhancement MRI and other MRI techniques can provide information beyond echocardiography for tissue characterization. MRI is increasingly being used for evaluation of genetically positive, phenotypically negative patients as well as for risk stratification.

Hypertrophic cardiomyopathy with restrictive phenotype and myocardial crypts

This report describes a 22-year-old woman who has clinical and physiologic features of a restrictive cardiomyopathy. Magnetic resonance imaging showed myocardial delayed enhancement and interventricular septal crypts characteristic of hypertrophic cardiomyopathy (HCM). Transcatheter biopsy confirmed the diagnosis, revealing marked myocyte hypertrophy, interstitial fibrosis, and fiber disarray, which are findings consistent with HCM. A review of the literature suggests that this is the first case of HCM reported with a restrictive pattern and myocardial crypts.

A new era in clinical genetic testing for hypertrophic cardiomyopathy

Building on seminal studies of the last 20 years, genetic testing for hypertrophic cardiomyopathy (HCM) has become a clinical reality in the form of targeted exonic sequencing of known disease-causing genes. This has been driven primarily by the decreasing cost of sequencing, but the high profile of genome-wide association studies, the launch of direct-to-consumer genetic testing, and new legislative protection have also played important roles. In the clinical management of hypertrophic cardiomyopathy, genetic testing is primarily used for family screening. An increasing role is recognized, however, in diagnostic settings: in the differential diagnosis of HCM; in the differentiation of HCM from hypertensive or athlete's heart; and more rarely in preimplantation genetic diagnosis. Aside from diagnostic clarification and family screening, use of the genetic test for guiding therapy remains controversial, with data currently too limited to derive a reliable mutation risk prediction from within the phenotypic noise of different modifying genomes. Meanwhile, the power of genetic testing derives from the confidence with which a mutation can be called present or absent in a given individual. This confidence contrasts with our more limited ability to judge the significance of mutations for which co-segregation has not been demonstrated. These variants of "unknown" significance represent the greatest challenge to the wider adoption of genetic testing in HCM. Looking forward, next-generation sequencing technologies promise to revolutionize the current approach as whole genome sequencing will soon be available for the cost of today's targeted panel. In summary, our future will be characterized not by lack of genetic information but by our ability to effectively parse it.