Élévation de troponine I à coronarographie normale chez un patient porteur d’une myopathie de Duchenne

Cardiomyopathy in Duchenne Muscular Dystrophy and the Potential for Mitochondrial Therapeutics to Improve Treatment Response

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by mutations to the dystrophin gene, resulting in deficiency of dystrophin protein, loss of myofiber integrity in skeletal and cardiac muscle, and eventual cell death and replacement with fibrotic tissue. Pathologic cardiac manifestations occur in nearly every DMD patient, with the development of cardiomyopathy-the leading cause of death-inevitable by adulthood. As early cardiac abnormalities are difficult to detect, timely diagnosis and appropriate treatment modalities remain a challenge. There is no cure for DMD; treatment is aimed at delaying disease progression and alleviating symptoms. A comprehensive understanding of the pathophysiological mechanisms is crucial to the development of targeted treatments. While established hypotheses of underlying mechanisms include sarcolemmal weakening, upregulation of pro-inflammatory cytokines, and perturbed ion homeostasis, mitochondrial dysfunction is thought to be a potential key contributor. Several experimental compounds targeting the skeletal muscle pathology of DMD are in development, but the effects of such agents on cardiac function remain unclear. The synergistic integration of small molecule- and gene-target-based drugs with metabolic-, immune-, or ion balance-enhancing compounds into a combinatorial therapy offers potential for treating dystrophin deficiency-induced cardiomyopathy, making it crucial to understand the underlying mechanisms driving the disorder.

Current state of cardiac troponin testing in Duchenne muscular dystrophy cardiomyopathy: review and recommendations from the Parent Project Muscular Dystrophy expert panel

Cardiac disease is now the leading cause of death in Duchenne muscular dystrophy (DMD). Clinical evaluations over time have demonstrated asymptomatic cardiac troponin elevations and acute elevations are associated with symptoms and cardiac dysfunction in DMD. Clinicians require a better understanding of the relationship of symptoms, troponin levels and progression of cardiac disease in DMD. As clinical trials begin to assess novel cardiac therapeutics in DMD, troponin levels in DMD are important for safety monitoring and outcome measures. The Parent Project Muscular Dystrophy convened an expert panel of cardiologists, scientists, and regulatory and industry specialists on 16 December 2019 in Silver Spring, Maryland and reviewed published and unpublished data from their institutions. The panel recommended retrospective troponin data analyses, prospective longitudinal troponin collection using high-sensitivity cardiac troponin I assays, inclusion of troponin in future clinical trial outcomes and future development of clinical guidelines for monitoring and treating troponin elevations in DMD.

Troponin I Levels Correlate with Cardiac MR LGE and Native T1 Values in Duchenne Muscular Dystrophy Cardiomyopathy and Identify Early Disease Progression

Cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Elevated troponin levels are observed in DMD and may vary with disease progression. We studied troponin levels in DMD related to cardiac fibrosis and native T1 measures. This is a prospective, cross-sectional, observational study of 30 DMD subjects measuring native T1 levels and late gadolinium enhancement (LGE) on cardiac MR imaging (CMR) correlated with temporally associated serum troponin I levels. Non-parametric analyses including Spearman correlations and Kruskal-Wallis test were performed between groups. p values resulting from the pair-wise comparisons were adjusted for multiple comparisons using the Sidak method where appropriate. There were 15 DMD subjects with no LGE (age 12 ± 3 yo; EF% 60 ± 5) and troponin I level of 0.05 ± 0.08 ng/ml, of which three had an abnormal troponin level (over 0.04 ng/ml); 7 DMD subjects with mild LGE (age 17 ± 5 yo, EF% 52 ± 8) and troponin I level of 0.28 ± 0.36 ng/ml, of which five had an abnormal troponin level; and 8 DMD subjects with moderate-to-severe LGE (age 16 ± 6 yo; EF% 54 ± 8) and troponin I level of 0.11 ± 0.14 ng/ml, of which four had an abnormal troponin level. Troponin I levels in DMD subjects with mild LGE was significantly increased compared to subjects with no LGE (p = 0.02). There was a statistically significant positive correlation between troponin I levels and MOLLI septal native T1 values (r² = 0.173, p = 0.02). Overall, MOLLI lateral native T1 levels were increased with moderate-severe LGE compared to mild and none (p < 0.01). Serum biomarker troponin I levels were increased in DMD subjects with mild LGE and correlated with MOLLI septal native T1 values. Troponin I levels may be a useful minimally invasive outcome marker to monitor myocardial disease progression in DMD cardiomyopathy.

DMD carrier model with mosaic dystrophin expression in the heart reveals complex vulnerability to myocardial injury

Duchenne muscular dystrophy (DMD) is a devastating neuromuscular disease that causes progressive muscle wasting and cardiomyopathy. This X-linked disease results from mutations of the DMD allele on the X-chromosome resulting in the loss of expression of the protein dystrophin. Dystrophin loss causes cellular dysfunction that drives the loss of healthy skeletal muscle and cardiomyocytes. As gene therapy strategies strive toward dystrophin restoration through micro-dystrophin delivery or exon skipping, preclinical models have shown that incomplete restoration in the heart results in heterogeneous dystrophin expression throughout the myocardium. This outcome prompts the question of how much dystrophin restoration is sufficient to rescue the heart from DMD-related pathology. Female DMD carrier hearts can shed light on this question, due to their mosaic cardiac dystrophin expression resulting from random X-inactivation. In this work, a dystrophinopathy carrier mouse model was derived by breeding male or female dystrophin-null mdx mice with a wild type mate. We report that these carrier hearts are significantly susceptible to injury induced by one or multiple high doses of isoproterenol, despite expressing ~57% dystrophin. Importantly, only carrier mice with dystrophic mothers showed mortality after isoproterenol. These findings indicate that dystrophin restoration in approximately half of the heart still allows for marked vulnerability to injury. Additionally, the discovery of divergent stress-induced mortality based on parental origin in mice with equivalent dystrophin expression underscores the need for better understanding of the epigenetic, developmental, and even environmental factors that may modulate vulnerability in the dystrophic heart.

Increases of cardiac troponin in conditions other than acute coronary syndrome and heart failure

BACKGROUND

Although cardiac troponin (cTn) is a cornerstone marker in the assessment and management of patients with acute coronary syndrome (ACS) and heart failure (HF), cTn is not diagnostically specific for any single myocardial disease process. This narrative review discusses increases in cTn that result from acute and chronic diseases, iatrogenic causes, and myocardial injury other than ACS and HF.

CONTENT

Increased cTn concentrations have been reported in cardiac, vascular, and respiratory disease and in association with infectious processes. In cases involving acute aortic dissection, cerebrovascular accident, treatment in an intensive care unit, and upper gastrointestinal bleeding, increased cTn predicts a longer time to diagnosis and treatment, increased length of hospital stay, and increased mortality. cTn increases are diagnostically and prognostically useful in patients with cardiac inflammatory diseases and in patients with respiratory disease; in respiratory disease cTn can help identify patients who would benefit from aggressive management. In chronic renal failure patients the diagnostic sensitivity of cTn for ACS is decreased, but cTn is prognostic for the development of cardiovascular disease. cTn also provides useful information when increases are attributable to various iatrogenic causes and blunt chest trauma.

SUMMARY

Information on the diagnostic and prognostic uses of cTn in conditions other than ACS and heart failure is accumulating. Although increased cTn in settings other than ACS or heart failure is frequently considered a clinical confounder, the astute physician must be able to interpret cTn as a dynamic marker of myocardial damage, using clinical acumen to determine the source and significance of any reported cTn increase.