Cardiac function in muscular dystrophy associates with abdominal muscle pathology

Background: The muscular dystrophies target muscle groups differentially. In mouse models of muscular dystrophy, notably the mdx model of Duchenne Muscular Dystrophy, the diaphragm muscle shows marked fibrosis and at an earlier age than other muscle groups, more reflective of the histopathology seen in human muscular dystrophy. Methods: Using a mouse model of limb girdle muscular dystrophy, the Sgcg mouse, we compared muscle pathology across different muscle groups and heart.Acohort of nearly 200 Sgcg mice were studied using multiple measures of pathology including echocardiography, Evans Blue dye uptake and hydroxyproline content in multiple muscle groups. Spearman rank correlations were determined among echocardiographic and pathological parameters. Findings: The abdominal muscles were found to have more fibrosis than other muscle groups, including the diaphragm muscle. The abdominal muscles also had more Evans blue dye uptake than other muscle groups. The amount of diaphragm fibrosis was found to correlate positively with fibrosis in the left ventricle, and abdominal muscle fibrosis correlated with impaired left ventricular function. Fibrosis in the abdominal muscles negatively correlated with fibrosis in the diaphragm and right ventricles. Together these data reflect the recruitment of abdominal muscles as respiratory muscles in muscular dystrophy, a finding consistent with data from human patients.