No cardiomyopathy in X-linked myopathy with excessive autophagy

Abstract

In X-linked myopathy with excessive autophagy (XMEA) progressive sarcoplasmic accumulation of autolysosomes filled with undegraded debris leads to atrophy and weakness of skeletal muscles. XMEA is caused by compromised acidification of lysosomes resulting from hypofunction of the proton pump vacuolar ATPase (V-ATPase), due to hypomorphic mutations in VMA21, whose protein product assembles V-ATPase. To what extent the cardiac muscle is affected is unknown. Therefore we performed a comprehensive cardiac evaluation in four male XMEA patients, and also examined pathology of one deceased patient's cardiac and skeletal muscle. None of the symptomatic men (aged 25-48 years) had history or symptoms of cardiomyopathy. Resting electrocardiograms and echocardiographies were normal. MRI showed normal left ventricle ejection fraction and myocardial mass. Myocardial late-gadolinium enhancement was not detected. The deceased patient's skeletal but not cardiac muscle showed characteristic accumulation of autophagic vacuoles. In conclusion, in classic XMEA the myocardium is structurally, electrically and clinically spared.

Keywords: Autolysosomes; Cardiomyopathy; Danon disease; Electron microscopy; Organellar acidification; X-linked myopathy with excessive autophagy.