Severe Hypertrophic Cardiomyopathy Research Articles

ALPK3 heterozygous truncating variants cause late-onset hypertrophic cardiomyopathy with frequent apical involvement and apical aneurysm.

Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous disorder with several established genotype-phenotype relationships. While biallelic truncating variants in the ALPK3 gene cause severe congenital HCM, recent studies have associated heterozygous truncating variants (ALPK3tv) with milder adult-onset HCM. Here we describe a multicenter cohort of 21 individuals with heterozygous ALPK3tv from 10 institutions in the United States, highlighting distinctive clinical characteristics compared to a control group of 132 patients with HCM caused by deleterious variants in sarcomeric genes. As compared to other HCM genotypes, ALPK3tv patients present at an older age (mean 57.25 years) with significantly lower left ventricular wall thickness (14.09 vs 19.78 mm with echocardiogram and 16.13 vs 21.13 mm with cardiac MRI), a lower prevalence of obstructive HCM (15% of ALPK3tv vs 45% of controls), and a strikingly higher incidence of apical aneurysm (22.22% vs. 2.40% in the control group). These results suggest a milder degree of hypertrophy in heterozygous ALPK3-related HCM as compared to other Mendelian causes of HCM, although the increased occurrence of apical aneurysms could have implications for ventricular arrhythmia risk. Our study underscores the importance of recognizing heterozygous ALPK3tv as a cause of adult-onset HCM and provides a comprehensive characterization of its clinical phenotype.

Cardiovascular magnetic resonance to differentiate veteran athlete's heart with cavity dilatation and mild dilated cardiomyopathy

Abstract Introduction Endurance athletic training may lead to left ventricular (LV) dilatation and mildly reduced resting LV function which can be difficult to differentiate from dilated cardiomyopathy (DCM). Myocardial fibrosis is increasingly recognised in lifelong athletes and is also prevalent in DCM where it confers adverse prognosis.(1,2) However, it is unknown whether the pattern and prevalence of fibrosis in athletes with cavity dilatation differs from DCM. In this study, we compared the CMR fibrosis distribution and tissue characteristics between athletic LV dilatation and mild DCM patients. Methods We prospectively recruited 113 males; 64 endurance athletes and 49 mild DCM patients. Inclusion criteria Age 50-80 years, LVEF 45-54% and LV end-diastolic volume indexed to body surface area (LVEDVi)≥110ml/m2. Athletes trained≥10 weekly hrs for≥15 yrs. Exclusion criteria; Chest pain, prior coronary revascularisation, severe valvular disease, myocarditis, hypertrophic cardiomyopathy, inducible ischaemia or myocardial infarction on CMR. CMR protocol included volumetric assessment, T1 mapping, quantitative stress perfusion and quantitative late gadolinium enhancement. Statistical analysis between groups was performed using unpaired t-test and receiver-operator curve (ROC) analysis. Results LVEDVi was not significantly different between athletes and mild DCM patients (123.3±12.6 vs 129.8±23.1ml/m2, P=0.057). However, LVEF (52.0±6.1 vs 47.6±5.2%, P<0.001) and right ventricular (RV) EDVi (121.0±14.3 vs 97.6±25.2ml/m2, P<0.001) were both greater in athletes. There was no difference in non-ischaemic fibrosis prevalence between both groups (50.0 vs 49.0%, P=0.915) nor the burden of fibrosis (3.5±2.9 vs 7.4±12.0g, P=0.087). However, the distribution of fibrosis varied with a significantly greater prevalence of basal mid-myocardial inferolateral fibrosis amongst athletes (87.5 vs 50.0%, P=0.002) whereas basal mid-myocardial inferoseptal fibrosis was significantly more common in mild DCM (45.8 vs 9.4%, P=0.002). Native T1 (1249.0±38.1 vs 1308.3±47.1ms, P<0.001) and extracellular volume (ECV) (22.0±2.1 vs 25.9±3.5%, P<0.001) were both lower in athletes than mild DCM patients. Furthermore, athletes had higher myocardial perfusion reserve (MPR) (3.65±1.30 vs 2.76±0.92, P<0.001) and stress myocardial blood flow (MBF) (2.09±0.70 vs 1.62±0.66, P<0.001). On ROC analysis, native T1 (area under curve (AUC) 0.89, P<0.001), ECV (AUC 0.85, P<0.001) and stress MBF (AUC 0.68, P<0.001) were able to differentiate athletes and mild DCM. Native T1 and ECV were significantly better at discriminating than MPR (P<0.001). Conclusion Myocardial fibrosis was highly prevalent in both veteran endurance athlete's heart and mild DCM whilst its distribution was distinctive between the groups. Native T1 and ECV were the best discriminators. Recognition of fibrosis patterns and associated tissue characteristics may be clinically useful to differentiate these two overlapping phenotypes.Figure 1; LGE distribution in athletes cFigure 2; CMR tissue characteristics to

Genotype-phenotype relationship in hypertrophic cardiomyopathy

Abstract Background/Introduction Hypertrophic cardiomyopathy (HCM) is an inherited highly heterogeneous disease with variable penetrance and expression, but the exact relationship between the underlying genetic cause and the clinical course remains elusive. Purpose The aim of our study was to analyse the phenotypic and molecular characteristics of individuals with HCM examined and treated at our University Hospital. Methods Clinical data from adult HCM patients treated at our hospital between 2005 and 2023 were analysed. Informed consents to participate in the study were obtained from all participants. Clinical manifestation, instrumental examination and next generation sequencing (NGS) data of HCM related genes were collected. The Mann–Whitney U for two groups and Kruskal–Wallis tests for more than two groups were used to compare continuous variables. Univariate logistic regression was used to analyze categorical variables. Results The study involved 191 unrelated individuals, 58.6% males, the median age at HCM diagnosis was 50, interquartile range 37 – 60 years. A median follow-up was 3.9 [1.6-6.4] years. Pathogenic and likely pathogenic (P/LP) variants were identified in 45.5% (N=87) of affected individuals. Truncating variants were observed in 31 individuals. MYBPC3 P/LP variants were the most common (N=47), following by MYH7 (N=22) and other (N=18). Individuals with MYBPC3 P/LP truncating variants had higher HCM estimated 5-year risk of sudden cardiac death (SCD) during primary evaluation (3.1 [2.5-4.6]) compared to individuals with P/LP variants in other genes (2.4 [1.9-3.7]) and individuals with negative NGS results (1.8 [1.5-2.7], p<0,001). Patients with MYBPC3 P/LP variants experienced the earliest onset of symptoms (median age 37.0 [30.5-50.0] years) and HCM diagnosis (median age 38.0 [31.0-51.5] years) compared to individuals with other genes P/LP variants (median age 46.0 [31.0-56.2] years and 47.5 [31.5 – 59.5] years, respectively) and genotype negative individuals (median age 51.5 [44.0-61.0] years and 52.0 [45.0-63.2] years, respectively), p>0,001). The presence of P/LP variant was associated with significantly thicker left ventricular wall (maximal thickness) on cardiac imaging in comparison with negative NGS results (18.0 [15.0-21.0] mm vs. 16.0 [14.0-18.0] mm, p=0.002 on transthoracic echocardiography and 20.0 [17.0-22.5] mm vs. 18.0 [16.0-20.0] mm, p<0,001 on cardiac magnetic resonance). The presence of MYBPC3 truncating variants were associated with the greatest risk of ventricular tachycardia in comparison with negative NGS results (OR 3.05, 95% CI:1.3, 8.0, p=0.025). Conclusion More severe HCM phenotype is associated with detection of P/LP variants in HCM related genes. The presence of the MYBPC3 P/LP variant is associated with an earlier onset of the disease and truncating variants of this gene are related to a higher risk for ventricular tachycardia and an estimated 5-year risk of SCD.

How much protection does clopidogrel provide to cats with hypertrophic cardiomyopathy?

Cats with hypertrophic cardiomyopathy (HCM) have a risk of developing aortic thromboembolism (ATE). Clopidogrel reduces the risk of redeveloping ATE and delays recurrence of ATE in cats that have experienced an ATE episode. Consequently, cardiologists have recommended administering clopidogrel to cats as a primary preventative, suggesting that all cats with severe HCM be administered clopidogrel. However, clopidogrel is unpalatable in its manufactured format, making such administration problematic for many clients. Therefore, estimating the potential benefit of administration might help clinicians determine on a case-by-case basis the need to treat cats with clopidogrel. Relatively simple statistical analyses of currently available data, along with certain assumptions and extrapolations, allow such an estimation of benefit in terms of relative and absolute risk reduction conferred by clopidogrel. Using this approach, and provided certain assumptions are true, clopidogrel likely confers a reduction in risk of ATE in cats with moderate to severe HCM of approximately 3% to 4%. Given the difficulty of administering clopidogrel to cats, clinicians should weigh these relatively small potential benefits against the potential harms (difficulty of administration) and not necessarily insist that clients administer clopidogrel.

Biallelic TYR and TKFC variants in Egyptian patients with OCA1 and new expanded TKFC features

BackgroundOculocutaneous albinism type1 (OCA1) is caused by the TYR gene's homozygous and compound heterozygous variants. TKFC gene variants cause triokinase & FMN cyclase deficiency syndrome with variable multisystemic disorders.ObjectivesTo determine the potential disease-causing variants in two deceased patients presenting atypical OCA1 features by demonstrating three generations for a single family. The two deceased neonates had severe skeletal abnormalities and fatal hypertrophic cardiomyopathy. We also explored the potential mechanisms for the causative relationship between TKFC and multisystem disorders.Patients and methodsDue to the new emerging symptoms that weren’t reported before with the TYR gene, the following methods were performed: Sanger sequencing for the TYR gene, followed by whole exome sequencing, co-segregation, and computational analyses.ResultsExtensive parental consanguinity was found, and consequently an autosomal recessive mode of inheritance was prioritized. Upon performing sequencing and segregation data, the following has been confirmed: positive co-segregation of nonsense homozygous NM_000372.5:c.346C > T p.(Arg116*) variant in TYR gene and multisystem disease-missense homozygous NM_015533.4:c.598G > A p.(Val200Ile) variant in TKFC gene in the two affected index patients who deceased due to hypertrophic cardiomyopathy. Using computational analysis, we found that c.598G > A p.(Val200Ile) pathogenicity has led to the failure of L2-K1 active site closure due to the potential differential fluctuation between valine and isoleucine residues. Subsequently, disruption of endogenous DHA phosphorylation was found. Two potential mechanisms exploring the causative relationship between TKFC gene and multisystem disorders have been suggested.ConclusionsThis study presented a first family with the co-existence of biallelic variants in TYR and TKFC genes associating severe skeletal abnormalities and lethal hypertrophic cardiomyopathy. Neither of these genes would have been pursued in the standard genetic counseling. Such discovery is paving the way for more efficient genetic counseling. Comparing TKFC results with literature data showed that our relevant expanded TKFC variant is the 3rd worldwide.

Carrying both the heterozygous Myh6-R453C and Tnnt2-R92W mutations aggravate the hypertrophic cardiomyopathy phenotype in mice

Hypertrophic cardiomyopathy (HCM) is an inherited disease of the heart muscle that is dominated by variations in eight genes encoding sarcomere proteins. Although there are clinical or basic research reports that carrying double mutations can lead to more severe HCM phenotypes, there are also research reports that after reanalyzing the reported mutations, the severity of clinical symptoms in patients with double mutations did not significantly increase compared to patients with only one mutation. To determine whether double pathogenic mutations can aggravate the phenotype of hypertrophic cardiomyopathy in mice, we constructed mice carrying single pathogenic heterozygous mutation Myh6-R453C or Tnnt2-R92W and mice carrying both pathogenic heterozygous mutations. Our results showed that mice with double heterozygous mutations exhibited significant hypertrophic cardiomyopathy phenotypes at 4 weeks of age, and the degree of hypertrophy was significantly higher than that of single heterozygous mutant mice of the same age. Our study suggests that carrying the two pathogenic heterozygous mutations simultaneously can aggravate the phenotype of HCM in mice, which provides experimental evidence for the genotype-phenotype relationship of double pathogenic mutations and provides reference significance for clinical risk stratification of HCM patients.

Avalglucosidase alfa in infantile-onset Pompe disease: A snapshot of real-world experience in Italy

IntroductionInfantile-onset Pompe disease (IOPD) is due to mutations in the GAA gene leading to profound deficiency of the lysosomal enzyme α-1,4-glucosidase. The disease is characterized by severe hypotonia, hypertrophic cardiomyopathy, macroglossia, and liver enlargement with onset in the first months of life. In the late-onset form (LOPD), muscle signs predominate with a clinical picture resembling muscle dystrophies. Enzyme replacement therapy with alglucosidase alfa (rhGAA) has been available since 2006 and patients treated with the enzyme show improved outcomes. Nevertheless, there is evidence that some patients have a suboptimal response or, after an initial improvement, reach a plateau with stabilization of the clinical picture. Thus, a new enzyme formulation, avalglucosidase alfa (neoGAA), with a higher degree of mannosylation, was developed. MethodsWe conducted a multicenter survey that collected data on four patients with IOPD, aged 6 to 16 years, who were switched to neoGAA thanks to a compassionate use program, after being treated for an average of 11.5 years with rhGAA. Follow-up data, including biochemical parameters and clinical features, were analyzed to determine clinical outcomes and the safety profile after a mean of 9 months. ResultsPatients with IOPD who were treated with neoGAA showed a positive change in biomarker levels. Moreover, the clinical picture revealed improved motor performance and cardiac parameters in patients who previously responded poorly. ConclusionThis study highlights the improved efficacy of neoGAA, as a next generation enzyme replacement therapy, in 4 Italian patients with IOPD. Several clinical parameters showed a positive response to the new formulation suggesting that, if used at diagnosis, neoGAA may result in better outcomes for patients with IOPD.

Early biomarkers of disease in hypertrophic cardiomyopathy: does telomere length matter?

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Biomedical Research Institute of Murcia (IMIB-Arrixaca) Introduction Hypertrophic cardiomyopathy (HCM) is the leading cause of sudden death in people under 35 years of age. (1) The variability of the phenotype together with its incomplete penetrance has been an obstacle to a complete understanding of the clinical spectrum and consequences of the disease. In recent years, there has been increasing interest in telomeric shortening and several authors have linked it to age-related diseases and HCM. (2, 3) Our aim was to study whether telomere length could affect the age at presentation and the severity of the HCM phenotype in genetic carriers. Methods Measurement of telomere length in circulating leukocytes (LTLc) was performed in 96 patients carrying a mutation in MYBPC3 causing HCM [58 affected (24 severely affected), 38 unaffected]. The variants included were c.2308+1G>A, p.Pro108Alafs*9, p.Arg891Alafs*160 and p.Glu258Lys, all considered founder mutations in our region. Peripheral venous blood samples were obtained from patients at the Inherited Heart Diseases Unit and stored at -80 ºC after informed consent had been signed by all participants. For telomere length analysis, a telomeric restriction fragment (TRF) assay was performed using the TeloTAGGGTelomereLenghtAssay kit (Roche, 12209136001) according to the manufacturer's protocol with slight modifications. Results Our results show a lower LTLc in those affected patients with a more severe HCM phenotype compared to the affected and unaffected group (p=0.023) independently of age and sex, which are two variables that affect LTLc. Similarly, a shorter telomere length was associated with greater severity of the phenotype, with patients presenting a larger left atrial size (p=0.032), septal size (p=0.023) and greater obstruction (p=0.044). The presence of atrial fibrillation (p=0.039) and sudden death (p=0.024) was also higher in patients with shorter telomeres. Conclusions Telomere length is a variable that influences the expression of the phenotype in HCM patients carrying a MYBPC3 variant. This is an observation that supports the thesis of numerous publications linking HCM and other age-related diseases, sometimes called telomeropathies,(2) to telomere shortening. It has also been linked to non-hereditary conditions(3). This fact sheds some light on the complex phenotypic variability present in HCM, raising LTL as a promising prognostic biomarker of the disease, as has already been suggested by other authors.(4, 5, 6).Workflow in the telomere legth analysisClinical associations of LTLc

Generation of induced pluripotent stem cells from an individual with early onset and severe hypertrophic cardiomyopathy linked to MYBPC3: c.772G > A mutation

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in the MYPBC3 gene, which encodes the cardiac myosin-binding protein C (cMyBP-C). Most pathogenic variants in MYPBC3 are either nonsense mutations or result in frameshifts, suggesting that the primary disease mechanism involves reduced functional cMyBP-C protein levels within sarcomeres. However, a subset of MYPBC3 variants are missense mutations, and the molecular mechanisms underlying their pathogenicity remain elusive. Upon in vitro differentiation into cardiomyocytes, induced pluripotent stem cells (iPSCs) derived from HCM patients represent a valuable resource for disease modeling. In this study, we generated two iPSC lines from peripheral blood mononuclear cells (PBMCs) of a female with early onset and severe HCM linked to the MYBPC3: c.772G > A variant. Although this variant was initially classified as a missense mutation, recent studies indicate that it interferes with splicing and results in a frameshift. The generated iPSC lines exhibit a normal karyotype and display hallmark characteristics of pluripotency, including the ability to undergo trilineage differentiation. These novel iPSCs expand the existing repertoire of MYPBC3-mutated cell lines, broadening the spectrum of resources for exploring how diverse mutations induce HCM. They additionally offer a platform to study potential secondary genetic elements contributing to the pronounced disease severity observed in this individual.

Influence of Clinical Aspects and Genetic Factors on Feline HCM Severity and Development.

Hypertrophic cardiomyopathy (HCM), which is associated with thickening of the left ventricular wall, is one of the most common heart pathologies in cats. This disease has a hereditary etiology and is primarily related to mutations in the MYBPC3 and MYH7 genes. This study aims to determine the effect of the presence of heterozygosity or homozygosity for the p. A31P mutation (c.91G>C) in the MYBPC3 gene in cats (Maine Coon) of different ages referring to the HCM severity and development, and to compare echocardiographic data and various clinical aspects for the most objective detection of disease in cats of different breeds. The incidence of HCM was 59% of the 103 cases of heart disease in cats in this study. In 23 cats diagnosed with HCM, cats heterozygous for the mutation accounted for 34%, and homozygous cats accounted for 26%. Cats homozygous for this mutation had moderate to severe HCM, suggesting an association with high penetrance of HCM and a significant risk of cardiac death in this group. The penetrance of the heterozygous type was lower than that of the homozygous genotype. This study also indicates that HCM has some age-related penetrance. The disease did not occur in the study group of cats aged up to 1 year, whereas at the age of 7 and older, the percentage of animals diagnosed with HCM was the highest and amounted to 44.3% of the total number of studied cats with HCM.

Endovascular treatment in Danon disease: a case report

BackgroundDanon disease is a lysosomal storage disorder with X-linked inheritance. The classic triad is severe hypertrophic cardiomyopathy, myopathy, and intellectual disability, with different phenotypes between both genders. Ischemic stroke is an uncommon complication, mostly cardioembolic, related to intraventricular thrombus or atrial fibrillation, among others.Case reportWe report the case of a 14-year-old Caucasian male patient with Danon disease who suffered from an acute ischemic stroke due to occlusion in the M1 segment of the middle cerebral artery. He underwent mechanical thrombectomy, resulting in successful revascularization with satisfactory clinical outcome. We objectified the intraventricular thrombus in the absence of arrhythmic events.ConclusionTo our knowledge, we report the first case of ischemic stroke related to Danon disease treated with endovascular treatment.

Association between Hypertrophic Cardiomyopathy and Variations in Sarcomere Gene and Calcium Channel Gene in Adults

Introduction: Calcium channel gene variations have been reported to be associated with hypertrophic cardiomyopathy (HCM) in family, but the relationship between calcium channel gene variations and HCM remains undefined in the population. Methods: A total of 719 HCM unrelated patients were initially enrolled. Finally, 371 patients were identified based on inclusion and exclusion criteria, including 145 patients with gene negative, 28 patients with a single rare calcium channel gene variation (calcium gene variation), 162 patients with a single pathogenic/likely pathogenic sarcomere gene variation (sarcomere gene variation) and 36 patients with a single pathogenic/likely pathogenic sarcomere gene variation and a single rare calcium channel gene variation (double gene variations). Then the demographic, electrocardiographic, echocardiographic, and follow-up data were collected. Results: Patients with double gene variations were at an earlier age and had more percent of family history of HCM, and had thicker walls, higher left ventricular outflow tract pressure gradient, more pathological Q waves, and more bundle branch blocks as compared with those with single sarcomere gene variation. During the follow-up period, patients with double gene variations had more primary endpoints than the other three groups (p = 0.0013). Multivariate analysis showed that double gene variations were the independent predictor of primary endpoint events in patients (HR: 4.82, 95% CI: 1.77–13.2; p = 0.002). Conclusion: We found that patients with double gene variations had more severe HCM phenotype and prognosis. The pathogenesis effects of sarcomere gene variation and calcium channel gene variation may be cumulative in HCM populations.

Innovation in surgical treatment of hypertrophic obstructive cardiomyopathy in children.

Hypertrophic cardiomyopathy is the second most common cardiomyopathy affecting children and adolescents and is the main cause of sudden death of young athletes. The natural prognosis of children with severe hypertrophic obstructive cardiomyopathy is not optimistic, and it is not uncommon for children with hypertrophic obstructive cardiomyopathy who do not respond to medication. Surgical treatment is often the only solution. Conventional surgical methods in the past include classic or modified extended Morrow operation, classic or modified Konno operation, and Ross-Konno operation. In recent years, with the development of minimally invasive surgery, various minimally invasive surgical methods have emerged endlessly. Because the incision of minimally invasive cardiac surgery is significantly smaller than that of traditional surgery, it causes less trauma, recovers quickly after surgery, and has the advantage of no difference in surgical effect compared with traditional median sternotomy. Tally endoscopic transmitral myectomy, RTM, minimally right thoracotomy, and other surgical methods have achieved encouraging results in adults and some older children with hypertrophic obstructive cardiomyopathy. The appearance of transapical beating-heart septectomy has brought the treatment of hypertrophic obstructive cardiomyopathy from the era of cardiopulmonary bypass and cardiac arrest to a new era of minimally invasive beating-heart surgery. In the past, there were few articles about the treatment of children with hypertrophic obstructive cardiomyopathy. This article reviewed the new progress and prognosis of surgical treatment of children with hypertrophic obstructive cardiomyopathy at home and abroad.

Metabolic profiling of aortic stenosis and hypertrophic cardiomyopathy identifies mechanistic contrasts in substrate utilization.

Aortic stenosis (AS) and hypertrophic cardiomyopathy (HCM) are distinct disorders leading to left ventricular hypertrophy (LVH), but whether cardiac metabolism substantially differs between these in humans remains to be elucidated. We undertook an invasive (aortic root, coronary sinus) metabolic profiling in patients with severe AS and HCM in comparison with non-LVH controls to investigate cardiac fuel selection and metabolic remodeling. These patients were assessed under different physiological states (at rest, during stress induced by pacing). The identified changes in the metabolome were further validated by metabolomic and orthogonal transcriptomic analysis, in separately recruited patient cohorts. We identified a highly discriminant metabolomic signature in severe AS in all samples, regardless of sampling site, characterized by striking accumulation of long-chain acylcarnitines, intermediates of fatty acid transport across the inner mitochondrial membrane, and validated this in a separate cohort. Mechanistically, we identify a downregulation in the PPAR-α transcriptional network, including expression of genes regulating fatty acid oxidation (FAO). In silico modeling of β-oxidation demonstrated that flux could be inhibited by both the accumulation of fatty acids as a substrate for mitochondria and the accumulation of medium-chain carnitines which induce competitive inhibition of the acyl-CoA dehydrogenases. We present a comprehensive analysis of changes in the metabolic pathways (transcriptome to metabolome) in severe AS, and its comparison to HCM. Our results demonstrate a progressive impairment of β-oxidation from HCM to AS, particularly for FAO of long-chain fatty acids, and that the PPAR-α signaling network may be a specific metabolic therapeutic target in AS.

Preclinical evaluation of CRISPR-based therapies for Noonan syndrome caused by deep-intronic LZTR1 variants

Gene variants in LZTR1 are implicated to cause Noonan syndrome associated with a severe and early-onset hypertrophic cardiomyopathy. Mechanistically, LZTR1 deficiency results in accumulation of RAS GTPases and, as a consequence, in RAS-MAPK signaling hyperactivity, thereby causing the Noonan syndrome-associated phenotype. Despite its epidemiological relevance, pharmacological as well as invasive therapies remain limited. Here, personalized CRISPR/Cas9 gene therapies might offer a novel alternative for a curative treatment in this patient cohort. In this study, by utilizing a patient-specific screening platform based on iPSC-derived cardiomyocytes from two Noonan syndrome patients, we evaluated different clinically translatable therapeutic approaches using small Cas9 orthologs targeting a deep-intronic LZTR1 variant to cure the disease-associated molecular pathology. Despite high editing efficiencies in cardiomyocyte cultures transduced with lentivirus or all-in-one AAVs, we observed crucial differences in editing outcomes in proliferative iPSCs versus non-proliferative cardiomyocytes. While editing in iPSCs rescued the phenotype, the same editing approaches did not robustly restore LZTR1 function in cardiomyocytes, indicating critical differences in the activity of DNA double-strand break repair mechanisms between proliferative and non-proliferative cell types and highlighting the importance of cell type-specific screens for testing CRISPR/Cas9 gene therapies.

Pompe disease in China: clinical and molecular characteristics.

Pompe disease (PD) is a rare, progressive, and autosomal recessive lysosomal storage disorder caused by mutations in the acid α-glucosidase gene. The clinical course and molecular mechanism of this disease in China have not been well defined. In this single-center cohort study, we investigated a total of 15 Chinese patients with Pompe disease to better understand the clinical manifestations, echocardiographic imaging and genetic characteristics in this population. The median age of 15 patients at symptom onset was 5.07 months (1-24 months). The median age at diagnosis was 19.53 months (range: 3 to 109 months, n = 15). Average diagnostic delay was 13.46 months. None of the patients had received enzyme replacement therapy (ERT). Fifteen patients died at a median age of 24.80 months due to cardiorespiratory failure (range 3-120 months). Myasthenia symptoms and severe hypertrophic cardiomyopathy were universally present (15/15 = 100%). Global longitudinal strain (GLS) by echocardiography was significantly lower in these patients. After adjusting for gender, body surface area (BSA), left ventricular ejection fraction (LVEF), E/e'ratio, maximum left ventricular wall thickness (MLVWT), left ventricular posterior wall (LVPW), left ventricular outflow tract (LVOT)gradient, GLS was independently correlated with survival time (hazard ratio (HR) = 0.702, 95% confidence Interval (CI): 0.532-0.925, P = 0.012). In our cohort, we identified 4 novel GAA mutation: c.2102T > C (p.L701P), c.2006C > T (p.P669l), c.766T > A (p.Y256N), c.2405G > T (p.G802V). 12 patients were compound heterozygotes, and 4 homozygotes. Our study provides a comprehensive examination of PD clinical course and mutations of the GAA gene for patients in China. We showed clinical utility of echocardiography in quantifying heart involvement in patients with suspected PD. GLS can provide prognostic information for mortality prediction. We reported four novel mutations in the GAA gene for the first time. Our findings may improve early recognition of PD characteristics in Chinese patients.

Neonatal hypertrophic cardiomyopathy with dyspnoea as the first symptom: a case report

Neonatal hypertrophic cardiomyopathy (HCM) is an idiopathic disease characterised by myocardial hypertrophy with normal or small ventricular chambers, a systolic hyperdynamic state and diastolic dysfunction. The etiology, pathogenesis and clinical manifestations of HCM are diverse, and it is likely to progress to sudden cardiac death. The highly heterogeneous nature of this disease determines the difficulty of its diagnosis, and it is especially rare to report that can be diagnosed conclusively in the neonatal period. However, when it does occur, the younger the age of onset is, the higher the mortality rate and the worse the prognosis. The genetic variants and diagnostic timing can affect the life course of the patient. This case report describes a neonate with a family history of HCM who was diagnosed with hypertrophic non-obstructive cardiomyopathy by echocardiography shortly after birth. At 4 years of age, the patient presented with slow weight gain, feeding difficulties, tachypnoea and diaphoresis, and cardiac ultrasound findings suggesting progression to severe hypertrophic obstructive cardiomyopathy, with a high likelihood of arrhythmias, heart failure, pulmonary hypertension, syncope and even sudden death. Neonatal congenital hypertrophic cardiomyopathy is extremely rare and difficult to diagnose before the onset of symptoms. Echocardiography has a definite diagnostic value in hypertrophic cardiomyopathy and helps in early detection and treatment. At the time of clinical diagnosis, children with hypertrophic cardiomyopathy should be asked about their family history and, if necessary, a survey of family members should be conducted for the early detection of mildly ill patients and gene carriers to enable timely intervention and treatment, which remains the focus of our research and efforts.

Abstract 14479: Compound Heterozygosity With Two Novel Mutations in MYBPC3 as a Cause of Severe and Early-Onset Hypertrophic Cardiomyopathy

Case presentation: A 8-year-old male was diagnosed with severe hypertrophic cardiomyopathy (HCM) after a cardiac arrest from which he was successfully defibrillated. Maximal wall thickness was 23 mm (z-score 6.36) on echocardiography. An implantable cardioverter defibrillator (ICD) was implanted and atenolol was started. After 4 ventricular fibrillation-terminating ICD shocks in the following 2 months, further treatment is under consideration. A genetic test identified the likely pathogenic intronic variant (c.1927+337G>T) in the MYBPC3 gene. An additional variant in the same gene (p.Arg817Gly), of uncertain significance but potentially relevant for the phenotype, was also found. His 10-year-old sister was also diagnosed with severe HCM, genetic test identified the two previously referred variants and ICD was also implanted. In the 4-year-old one sister, who is apparently healthy, only the likely pathogenic intronic variant (c.1927+337G>T) was found. Regarding their parents, both with no evidence of cardiomyopathy, c.1927+337G>T variant was identified in the father, while p.Arg817Gly was present in the mother. Discussion: This clinical case is noteworthy as an example of compound heterozygosity in which each parent donates one alternate allele, being these alleles located at different loci within the same gen, which emphasizes the importance of family genetic testing. The variant of uncertain significance p.Arg817Gly appears to be a disease modifier, causing the phenotype to be expressed early and severely in the presence of the probably pathogenic intronic variant c.1927+337G>T in MYBPC3. This deep intronic variant has not been described previously but was found in thirteen index cases referred for HCM and a history of familial sudden death at an early age, being overrepresented in the cohort of HCM in the north of Spain. Being a carrier of both these two novel variants appears to cause an extremely aggressive childhood-onset phenotype.

Abstract 12080: Comprehensive Proteomics Profiling of Human Myocardium Reveals Signaling Pathways Dysregulated in Severe Forms of Hypertrophic Cardiomyopathy

Introduction: Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease, affecting 1 in 200-500 people. There is significant heterogeneity in disease severity. The signaling pathways that link gene mutations to severe HCM disease remain unknown. Analysis of the myocardial proteome is a novel approach to understanding severe forms of HCM. Hypothesis: Comprehensive proteomics profiling of myocardium identifies signaling pathways that are differentially regulated in severe forms of HCM. Methods: Proteomics profiling of 7289 proteins from myocardium was performed on patients with HCM. Univariable analysis with the Wilcoxon rank sum test or Spearman’s rank correlation test was used to determine the association between protein concentration and 5 clinical indicators of severe HCM: 1) left ventricular ejection fraction (LVEF), 2) atrial fibrillation (AF), 3) ventricular arrhythmias, 4) maximum septal thickness, and 5) late gadolinium enhancement (LGE) by cardiac magnetic resonance (CMR). Pathway analysis of proteins with significantly different concentrations (i.e., nominal p<0.05) in association with each clinical indicator was executed. Results: There were 106 patients with HCM included in the study. Pathway analysis of proteins associated with each indicator of severe HCM revealed dysregulation of inflammatory pathways and Ras-MAPK-related pathways ( Figure ). Metabolic pathways and adhesion pathways were dysregulated in association with LVEF and AF. Dysregulation of angiogenesis pathways (e.g., HIF-1, VEGF) was associated with LGE (FDR<0.05). Conclusions: Comprehensive proteomics profiling of human HCM myocardium was used to identify dysregulated signaling pathways associated with clinical features of severe HCM. Findings from this study support the role of both known (e.g., inflammation, metabolism, adhesion, and angiogenesis) and novel (e.g., Ras-MAPK) pathways in the development of severe forms of HCM.

Abstract 15732: Chronic Mavacamten Treatment Has Opposing Effects on Contractility in Engineered Heart Tissue Models of Severe vs. Mild Hypertrophic Cardiomyopathy

Many hypertrophic cardiomyopathy (HCM) causing mutations result in myocardial hypercontractility by increasing the number of myosin crossbridges in the disordered relaxed (DRX) state, or by sensitizing the sarcomere to the effects of Ca 2+ . Mavacamten (Mava) recently became the first FDA-approved treatment of obstructive HCM that directly targets hypercontractility by reducing the number of DRX cross bridges. Mava improves outcomes in patients with obstructive HCM but has not been approved in children or adults without obstructive HCM. The efficacy of chronic Mava treatment at preventing phenotype development in asymptomatic HCM mutation carriers remains largely unexplored. We recently showed that ablation of cardiac myosin binding protein-C (cMyBP-C -/-) in engineered heart tissue (EHT) causes rapid phenotype development in a dish. Initial hypercontractility progresses to hypocontractility with impaired relaxation, mediated by Ca 2+ mishandling. Here we investigate whether chronic Mava administration prevents phenotype progression. cMyBP-C +/+, +/- and -/- EHT were treated with 100nM Mava starting on day 7 of EHT culture. Serial twitch force (TF) measurements were performed weekly for 5 weeks, using the Mantarray platform. At day 7, prior to Mava treatment, +/- and -/- produced significantly more TF than +/+ EHT (392 ± 9 μN vs. 390 ± 15 μN vs. 199 ± 13 μN). At day 14, Mava treatment reduced TF by 31% (p < 0.001) in +/+ EHT, 30% (p < 0.001) in +/- EHT and 12% (p = 0.115) in -/- EHT. After an additional 4 weeks, chronic Mava treatment reduced TF by 54% (p < 0.001) in +/+ EHT, 65% (p < 0.001) in +/- EHT but increased TF by 23% (p = 0.034) in -/- EHT.These data show that chronic Mava treatment prevents/slows maladaptive remodeling in -/- EHT, but depresses contractility in +/+ and +/- ECT, suggesting that chronic Mava treatment may be detrimental to patients with mild HCM. Our ongoing studies are assessing the effect of chronic Mava treatment on other EHT models of HCM and on Ca 2+ -handling.