Cardiac troponin T Arg92Trp mutation and progression from hypertrophic to dilated cardiomyopathy

BACKGROUND: Mutations in the cardiac troponin T gene causing familial hypertrophic cardiomyopathy (HCM) are associated with a very poor prognosis but only mild hypertrophy. To date, the serial morphologic changes in patients with HCM linked to cardiac troponin T gene mutations have not been reported. HYPOTHESIS: The aim of this study was to determine the long-term course of patients with familial HCM caused by the cardiac troponin T gene mutation, Arg92Trp. METHODS: In all, 140 probands with familial HCM were screened for mutations in the cardiac troponin T gene. RESULTS: The Arg92Trp missense mutation was present in 10 individuals from two unrelated pedigrees. They exhibited different cardiac morphologies: three had dilated cardiomyopathy-like features, five had asymmetric septal hypertrophy with normal left ventricular systolic function, one had electrocardiographic abnormalities without hypertrophy, and one had the disease-causing mutation but did not fulfill the clinical criteria for the disease. The mean maximum wall thickness was 14.1 +/- 6.0 mm. The three patients with dilated cardiomyopathy-like features had progressive left ventricular dilation. Three individuals underwent right ventricular endomyocardial biopsy. There was a modest degree of myocardial hypertrophy (myocyte diameter: 18.9 +/- 5.2 microm), and minimal myocardial disarray and mild fibrosis were noted. CONCLUSION: The Arg92Trp substitution in the cardiac troponin T gene shows a high degree of penetrance, moderate hypertrophy, and early progression to dilated cardiomyopathy in Japanese patients. Early identification of individuals with this mutation may provide the opportunity to evaluate the efficacy of early therapeutic interventions.     

A new mutation of the cardiac troponin T gene causing familial hypertrophic cardiomyopathy without left ventricular hypertrophy

AIM—To screen for a mutation of the cardiac troponin T gene in two families where there had been sudden deaths without an increase in left ventricular mass but with myocardial disarray suggesting hypertrophic cardiomyopathy.
METHODS—DNA from affected individuals from both families was used to screen the cardiac troponin T gene on an exon by exon basis. Mutation screening was achieved by polymerase chain reaction and direct sequencing. Where appropriate, a mutation was confirmed by restriction digest.
RESULTS—A novel missense mutation of exon 9 was found in the affected individuals of one of the families. This mutation at amino acid 94 resulted in the substitution of arginine for leucine and was not found in 100 normal control samples. A mutation of the cardiac troponin T gene was excluded in the second family.
CONCLUSIONS—A mutation of the gene for the sarcomeric protein cardiac troponin T can cause familial hypertrophic cardiomyopathy with marked myocyte disarray and frequent premature sudden death in the absence of myocardial hypertrophy at clinical or macroscopic level.


Keywords: hypertrophic cardiomyopathy; troponin T     

Autopsy findings in siblings with hypertrophic cardiomyopathy caused by Arg92Trp mutation in the cardiac troponin T gene showing dilated cardiomyopathy-like features

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is caused by mutations in the genes that encode sarcomeric proteins. Although some patients with HCM have shown dilated cardiomyopathy (DCM)-like features, the relationship between genotype and histologic findings is not well known. HYPOTHESIS: Family members with the same gene mutation may show the same histopathologic changes and clinical manifestations. METHODS: Siblings with HCM caused by an Arg92Trp mutation in the cardiac troponin T gene, showing DCM-like features, were examined. RESULTS: The patients were a 69-year-old woman and her 57-year-old brother who both died from congestive heart failure. Their autopsies revealed the same histopathologic findings in the heart. The anterior walls and interventricular septa of their hearts were replaced with extensive fibrosis and showed thinning. Myocyte hypertrophy, disarray, and thickened medial walls of the intramural coronary arteries were found. On electron microscopy, the number of mitochondria was seen to be increased and they formed many clusters. CONCLUSIONS: Patients with HCM caused by an Arg92Trp mutation in the cardiac troponin T gene may have the same histopathologic findings, which may result in DCM-like features.     

Clinical features of hypertrophic cardiomyopathy caused by an Arg278Cys missense mutation in the cardiac troponin T gene

To further examine the genetic and clinical features of hypertrophic cardiomyopathy caused by mutations in the cardiac troponin T (cTnT) gene, we screened 143 probands from our hypertrophic cardiomyopathy population for mutations in this gene. We report that the Arg278Cys missense mutation in the cTnT gene had a different clinical presentation in 2 different families and was associated with a clinical profile that deviates from what is currently expected for cTnT gene mutations.     

Transgenic modeling of a cardiac troponin I mutation linked to familial hypertrophic cardiomyopathy

Multiple mutations in cardiac troponin I (cTnI) have been associated with familial hypertrophic cardiomyopathy. Two mutations are located in the cTnI inhibitory domain, a highly negatively charged region that alternately binds to either actin or troponin C, depending on the intracellular concentration of calcium. This region is critical to the inhibition of actin-myosin crossbridge formation when intracellular calcium is low. We modeled one of the inhibitory domain mutations, arginine145-->glycine (TnI(146Gly) in the mouse sequence), by cardiac-specific expression of the mutated protein in transgenic mice. Multiple lines were generated with varying degrees of expression to establish a dose relationship; the severity of phenotype could be correlated directly with transgene expression levels. Transgenic mice overexpressing wild-type cTnI were generated as controls and analyzed in parallel with the TnI(146Gly) animals. The control mice showed no abnormalities, indicating that the phenotype of TnI(146Gly) was not simply an artifact of transgenesis. In contrast, TnI(146Gly) mice showed cardiomyocyte disarray and interstitial fibrosis and suffered premature death. The functional alterations that seem to be responsible for the development of cardiac disease include increased skinned fiber sensitivity to calcium and, at the whole organ level, hypercontractility with diastolic dysfunction. Severely affected lines develop a pathology similar to human familial hypertrophic cardiomyopathy but within a dramatically shortened time frame. These data establish the causality of this mutation for cardiac disease, provide an animal model for understanding the resultant pathogenic structure-function relationships, and highlight the differences in phenotype severity of the troponin mutations between human and mouse hearts.     

Prevalence and determinants of elevated high-sensitivity cardiac troponin T in hypertrophic cardiomyopathy

BackgroundThis study was designed to evaluate the prevalence and determinants of increased high-sensitivity cardiac troponin T (hs-cTnT) as a marker of cardiac injury in patients with hypertrophic cardiomyopathy (HCM).MethodsA total of 98 consecutive patients with HCM (71.4% males; mean age 51.18 ± 15.47 years) between 2012 and 2013 were evaluated by measuring the level of serum hs-cTnT along with other clinical assessments.ResultsThere were 42 (42.9%) patients with a minimum serum hs-cTnT level of 14 ng/L. The mean hs-cTnT level was 12.37 ng/L (6.94–24.26 ng/L). There were significant differences in chest pain New York Heart Association functional class, left ventricular hypertrophy in the surface electrocardiogram, non-sustained ventricular tachycardia in 24-h electrocardiogram-Holter monitoring, left atrial (LA) area index, ratio of peak early (E) transmitral filling velocity to peak early diastolic annular velocity (Ea septal) at the level of the septal mitral annulus (E/Ea septal), maximum left ventricular (LV) wall thickness ≥ 30 mm, and peak LV outflow gradient ≥ 30 mmHg in echocardiography between the patients with hs-cTnT < 14 ng/L and those with hs-cTnT ≥ 14 ng/L. However, after multivariate analysis, age, maximum LV wall thickness, LA area index, and E/Ea septal remained as the independent determinants of elevated hs-cTnT in HCM.ConclusionsThe results demonstrated that hs-cTnT was elevated in a significant number of our HCM patients; therefore, hs-cTnT can be introduced as a valuable marker of myocardial injury in HCM patients.     

Mutations in the cardiac troponin T gene show various prognoses in Japanese patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder resulting from mutations in genes for at least 15 various sarcomere-related proteins including cardiac β-myosin heavy chain, cardiac myosin-binding protein C, and cardiac troponin T. The troponin T gene (TNNT2) mutation has the third incidence of familial HCM, and the genotype–phenotype correlation of this gene still remains insufficient in Japanese familial HCM. Therefore, in the present study, we focused on screening the TNNT2 mutation in 173 unrelated Japanese patients with familial HCM, and found three reported mutations and a new mutation of TNNT2 in 11 individuals from four families. In these families, two individuals from one family had double mutations, Arg130Cys and Phe110Ile, six individuals from two other families had an Arg92Trp mutation, and one individual of another family had a new mutation, Ile79Thr, of TNNT2. The phenotype of each family was often different from reported cases, even if they had the same genetic mutation. In addition, families with the same genetic mutation showed a similar trend in the phenotype, but it was not exactly the same. However, sudden death in youth was observed in all of these families. Although the type of genetic mutation is not useful for predicting prognosis in HCM, the possibility of sudden cardiac death remains. Therefore, the prognosis of individuals bearing the TNNT2 mutation with familial HCM should be more carefully observed from birth.     

心脏肌钙蛋白T对扩张性心肌病患者的预测价值

目的探讨心脏肌钙蛋白T(cTnT)对扩张性心肌病(DCM)的预测价值。方法用酶联免疫法测定60例DCM患者的血清cTnT水平并将患者分为cTnT升高组和cTnT正常组;观察其两组恶性心律失常,心源性死亡和因心衰再入院的发生率。结果在60例DCM患者中,cTnT升高26例(43.3%),cTnT升高组恶性心律失常,因心衰再入院的发生率显著高于cTnT正常组(P<0.01)。cTnT升高对因心衰再入院的阳性预测值为30.7%,阴性预测值为96%。结论cTnT对扩张性心肌病的预后相关。     

Serum levels of high-sensitivity troponin T: a novel marker for cardiac remodeling in hypertrophic cardiomyopathy

BackgroundHypertrophic cardiomyopathy (HCM) is characterized by inappropriate hypertrophy, small-vessel coronary artery disease, myocyte disarray, and increased interstitial fibrosis. High-sensitivity troponin T (hs-TnT) could be a reliable indicator of myocardial remodeling, a proposed prognostic marker in HCM. Therefore we hypothesized that increased hs-TnT levels are related to different variables associated with myocardial remodeling, such as the presence of fibrosis assessed with cardiac magnetic resonance imaging (MRI).Methods and ResultsWe included 95 hemodynamically stable HCM patients, 72 male, aged 45.7 ± 14.2 years, and 45 healthy control subjects with similar age and gender. A complete history and clinical examination was performed, including 12-lead electrocardiogram (ECG), echocardiography, 24-hour ECG-Holter monitoring, symptom-limited treadmill exercise test, and late gadolinium enhancement in cardiac MRI. Risk factors for sudden death were evaluated. A blinded cardiac MRI was performed with late gadolinium enhancement study. Serum hs-TnT levels were assayed. A high proportion (42%) of hemodynamically stable patients studied showed increased levels of hs-TnT. The hs-TnT levels were raised in patients with severe dyspnea: New York Heart Association (NYHA) functional class ≥3 (P = .020), outflow obstruction (P = .013), systolic dysfunction (P = .037), abnormal blood pressure response (P = .036), and presence of gadolinium enhancement (P = .021). The hs-TnT levels correlated positively with the maximum left ventricular wall thickness (r = 0.47; P < .001), left atrial diameter (r = 0.36, P = .014), and outflow gradient (r = 0.28; P = .008).ConclusionsA high proportion of hemodynamically stable patients show increased levels of hs-TnT. We observed that raised hs-TnT serum levels are associated with different conditions related to the severity of the disease.     

肥厚型心肌病患者心脏肌钙蛋白T基因变异及其相关临床表型分析

目的 探讨中国人群肥厚型心肌病(HCM)患者中心脏肌钙蛋白T(cardiac troponin T,TNNT2)基因变异的情况,并分析基因型与临床表型的关系.方法 对100例确诊为HCM的患者及部分家属进行临床评估分析并随访,聚合酶链反应扩增所有编码序列及内含子-外显子拼接部位,直接测序法分析TNNT2基因多态/突变情...     

Molecular insights from a novel cardiac troponin I mouse model of familial hypertrophic cardiomyopathy

Gene mutations in cardiac troponin I (cTnI) account for up to 5% of genotyped families with familial hypertrophic cardiomyopathy (FHC). Little is known about how cTnI mutations cause disease. Five lines of transgenic mice were generated which overexpress the human disease-causing cTnI gene mutation, Gly203Ser (designated cTnI-G203S), in a cardiac-specific manner. Mice were compared to transgenic mice that overexpress normal cTnI (cTnI-wt) and non-transgenic littermates (NTG). cTnI-G203S mice developed all the characteristic features of FHC by age 21 weeks. Left ventricular hypertrophy was observed on echocardiography (1.25+/-0.05 mm vs. 0.86+/-0.02 mm in cTnI-wt, P<0.01), associated with a significant 4-fold increase in RNA markers of hypertrophy, ANF and BNP. Myocyte hypertrophy, myofiber disarray and interstitial fibrosis were observed in cTnI-G203S mice. Expression of the cTnI-G203S mutation in neonatal cardiomyocytes resulted in a significant increase in myocyte volume, and reduced interactions with both troponins T and C. Ca2+ cycling was abnormal in adult cardiomyocytes extracted from cTnI-G203S mice, with a prolonged decay constant in Ca2+ transients and a reduced decay constant in response to caffeine treatment. Mice with the cTnI-G203S gene mutation develop all the phenotypic features of human FHC. The cTnI-G203S mutation disrupts interactions with partner proteins, and results in intracellular Ca2+ dysregulation early in life, suggesting a pathogenic role in development of FHC.     

Deletion in the cardiac troponin I gene in a family from northern Sweden with hypertrophic cardiomyopathy

The cardiac troponin I gene has been described to be associated with hypertrophic cardiomyopathy. Until now, mutations in this gene have been found only in the Japanese population. We now present the first non-Japanese family, from northern Sweden, with a mutation in the cardiac troponin I gene. Clinical diagnose was based on echocardiography, with a maximum left ventricular wall thickness of >13 mm, or major electrocardiographic abnormalities, excluding subjects with other known causes of cardiac hypertrophy. Mutation screening was performed with a single-strand conformation polymorphism analysis and identification of mutation by direct DNA sequencing. We have identified a 33-bp deletion in exon 8 encompassing the stop codon. Nine individuals in three generations were tested, and four were carriers of this deletion. The mother was genetically affected and died of heart failure aged 90. Echocardiography at 71 years of age revealed no hypertrophy, but the electrocardiogram showed signs of left ventricular hypertrophy. Her two sons, also genetically affected, had left ventricular hypertrophy, with maximum wall thickness of 15 and 16 mm, respectively. One daughter and four grandchildren were clinically unaffected, but one of them, a 27-year-old woman with maximum wall thickness of 8 mm and normal electrocardiogram, was found to be genetically affected. In conclusion, we describe a non-Japanese family in which hypertrophic cardiomyopathy is due to a genetic defect in the cardiac troponin I gene. This mutation is a deletion of 33 bp in the last exon, whereas the previously described mutations in this gene are single nucleotide changes and a single codon deletion. The deletion of the C-terminal part of the cardiac troponin I protein, seems in this particular family to be associated with a mild phenotypic expression of familial hypertrophic cardiomyopathy.     

Septal wall thinning and systolic dysfunction in patients with hypertrophic cardiomyopathy caused by a cardiac troponin I gene mutation

Background Lysine 183 deletion in the cardiac troponin I gene is 1 of the mutations that causes hypertrophic cardiomyopathy (HCM). However, the clinical course and determinants of poor prognosis in patients with this mutation have not been well established. Methods and Results We analyzed 10 probands with HCM caused by this mutation and their family members. Forty-six of these 79 subjects were found to be carriers, and 33 were non-carriers. All non-carriers had a percent fractional shortening (%FS) of >25% at all ages. By contrast, 7 of 24 carriers >40 years of age had a %FS of <25%, and no carriers <40 years of age had a %FS of <25%. The change in interventricular septal thickness and the change in %FS were significantly correlated (R = 0.758; P = .0017). Conclusion These results suggest that about 30% of patients with HCM caused by a lysine 183 deletion mutation in the cardiac troponin I gene have systolic dysfunction develop after 40 years of age, and that patients with this mutation whose interventricular septal thickness shows a serial decrease should be followed-up closely for development of systolic dysfunction. (Am Heart J 2002;143:690-5.)