Advanced pathological study for definite diagnosis of mitochondrial cardiomyopathy

AimsMitochondrial cardiomyopathy (MCM) is difficult to make a definite diagnosis because of various cardiovascular phenotypes and no diagnostic criteria in the pathology examination. We aim to add myocardial pathology to the diagnostic criteria for mitochondrial respiratory chain disorders.MethodsQuantitative analysis of mitochondria using electron microscopy and immunohistopathological analysis with respiratory chain enzyme antibodies were performed in 11 patients with hypertrophic or restrictive cardiomyopathy who underwent endomyocardial biopsy for possible MCM . Respiratory chain enzymatic assay in biopsied myocardium and genetic studies were also performed in all the subjects to define MCM.ResultsFour patients were diagnosed with MCM according to the recent criteria of mitochondrial respiratory chain disorders. Using electron microscopy with quantitative analysis, the volume density of mitochondria within cardiac muscle cells was significantly increased in the MCM group compared with the non-MCM group (p=0.007). Immunohistopathological results were compatible with the result of the respiratory chain enzymatic assay.ConclusionsPathological diagnosis of MCM could be confirmed by a quantitative study of electron microscopy and immunohistopathological analysis using the mitochondrial respiratory chain enzyme subunit antibody.

Cardiac involvement in children with respiratory chain disorders

In their article, Yaplito-Lee et al. reported about the cardiac findings in 89 children with mitochondrial disorders (MIDs) [1]. This retrospective study raises some concerns. It would be useful to know if all cardiac investigations applied to assess cardiac involvement (CI) were carried out in each of the 89 patients. We should be informed if focal myositis mentioned in table 2 was attributed to the underlying mitochondrial disorder as MIDs may induce inflammatory reactions [2]. It should be also explained why the “structural heart defect” was not attributed to the underlying disorder.