Cardiac troponin-I, a sarcomeric regulatory protein integral to skeletal and cardiac muscle contraction, has long been utilized as a diagnostic and prognostic biomarker of heart disease. For muscular dystrophies, elevated serum creatine kinase and troponin are associated with myopathic changes in muscle. Understanding the sensitivity of the analytical tools, as well as the types of cardiac issues that may result in elevated cardiac markers in serum, is critical to use of these assays in monitoring myotonic dystrophy type 1 (DM1) patients.
The constellation of cardiac involvement in DM1 includes atrioventricular block, prolonged QT interval, prolonged QRS interval, increased ventricular premature contractions, atrial fibrillation/flutter, right/left bundle branch block, non-sustained ventricular tachycardia and left ventricular systolic dysfunction (Petri et al., Int. J. Cardiol. 160: 82-88, 2012). Prior reports identified a correlation between CTG repeat length and cardiac dysfunction and linked the degree of neuromuscular and cardiac involvement in patients.
A large multi-center study in Scotland recently reported out an analysis of serum levels of cardiac troponin-I (cTnI) in a cohort of 117 well-characterized DM1 patients recruited from outpatient clinics. Nine subjects had cTnI levels that exceeded the 99th percentile of the general population. One-third of subjects with elevated cTnI also had left ventricular systolic dysfunction. The authors noted that elevations in cTnI did not correlate with CTG length, were not predictive of severe conduction abnormalities and did not correlate with muscle strength (by MIRS score). There also was no association between cTnI level and the presence of an implanted cardiac device.
Overall, the authors suggest that cTnI levels represent a potential biomarker to assess risks in the management of DM1 patients and for stratification of subjects in clinical trials. Although the lack of correlation of cTnI levels and MIRS score suggests a cardiac origin for elevated serum cTnI, the underlying responsible pathology in the context of known cardiac phenotype of DM1 is currently unclear. Finally, the authors suggest that the overall sample of patients with elevated cTnI is small and propose these findings as exploratory, requiring follow-up of this and other putative cardiac biomarkers in larger cohorts.
Elevated Plasma Levels of Cardiac Troponin-I Predict Left Ventricular Systolic Dysfunction in Patients with Myotonic Dystrophy Type 1: A Multicentre Cohort Follow-up Study.
Hamilton MJ, Robb Y, Cumming S, Gregory H, Duncan A, Rahman M, McKeown A, McWilliam C, Dean J, Wilcox A, Farrugia ME, Cooper A, McGhie J, Adam B, Petty R; Scottish Myotonic Dystrophy Consortium., Longman C, Findlay I, Japp A, Monckton DG, Denvir MA. PLoS One. 2017 Mar 21;12(3):e0174166. doi: 10.1371/journal.pone.0174166.