Response to Letter Regarding Article, “Cardiomyopathy in a Duchenne Muscular Dystrophy Carrier and Her Diseased Son: Similar Pattern Revealed by Cardiovascular MRI”
We appreciated the interest of Drs Giglio and Mangiola in our muscular dystrophy (MD) case report.1 We agree with the suggestion of White et al2 that for clinical diagnosis, duplications in the dystrophin gene should be treated with special care. Indeed, multiplex ligation-dependent probe amplification was performed in both the child with Duchenne muscular dystrophy (DMD) and his mother, proving the diagnosis. We also mentioned in our article that serum creatine kinase levels were elevated in the DMD carrier mother. However, we do not agree with Drs Giglio and Mangiola’s opinion that “skewed X-chromosome inactivation assay must be performed because this factor is currently believed to be a main contributor to phenotypic manifestations in a Duchenne carrier.” We do not consider the work of Yoshioka et al3 to be compelling evidence because this study was based on only 9 MD carriers. In contrast, another study comprising 107 MD carriers clearly suggested that a highly skewed X-chromosome pattern in blood is not enough to predict the phenotypic development of muscular weakness in MD carriers.4 Hence, we think that not performing this analysis in the reported patients was justified.
Classifying cardiomyopathy on the basis of ejection fraction may only underestimate the extent of disease that is most evident in patients with hypertrophic cardiomyopathy. In our opinion, both mother and child have advanced cardiomyopathy because late gadolinium enhancement (LGE) cardiovascular MRI already revealed significant myocardial tissue damage (LGE in the child, 12.0%; in the mother, 17.6% of left ventricular mass). These areas of LGE were previously shown to represent the critical substrate for malignant arrhythmias in patients with nonischemic cardiomyopathy.5 Future studies have to evaluate whether measurement of LGE might even be superior to the measurement of left ventricular ejection fraction relative to accurate risk prediction in MD patients and carriers.
When preparing Figure 3 in our article, we intentionally chose images of a patient with Becker MD because, as outlined by Drs Giglio and Mangiola, dystrophin immunostaining of this subject showed a mosaic pattern (feature of DMD carrier and/or a patient with Becker MD) and the absence of dystrophin in most cardiomyocytes (feature of a patient with DMD). We think that this patient nicely illustrates the features present in both the DMD child and his carrier mother.
Regarding the frequency and clinical value of LGE and its association with the severity of cardiomyopathy in MD carriers, we are currently preparing a manuscript that will emphasize the clinical value of our observation in this case report and further explore the questions raised by Drs Giglio and Mangiola about this interesting issue.
Source of Funding
This work was financially supported by a grant from the German Heart Foundation (Deutsche Stiftung für Herzforschung, grant-ID F/15/07 to Dr Yilmaz).