Endocardial fibroelastosis in mucopolysaccharidosis type VI

This case report describes two siblings less than 1 year of age who presented severely ill with a dilated cardiomyopathy. Full blood examination in both cases revealed marked granularity of neutrophils suggestive of mucopolysaccharidosis type VI. There were no physical features of a mucopolysaccharidosis but biochemical evaluation confirmed mucopolysaccharidosis type VI in both children. Autopsy in one patient confirmed endocardial fibroelastosis and electron microscopy of fibreblasts in the myocardium showed distention with membrane‐bound vacuoles, consistent with a mucopolysaccharidosis. These siblings developed endocardial fibroelastosis before other clinical manifestations of the mucopolysaccharidosis. Assessment for metabolic causes of a cardiomyopathy is important, as cardiac disease may be the initial manifestation of a metabolic disease.