Until recently, the contribution of inherited metabolic diseases to conditions presenting primarily with symptoms of cardiac disease would have been considered to be small, and devoting an entire chapter of a clinical text like this to them would have been considered unusual. However, over the past 15 years, presentation as serious cardiac disease has become associated in particular with two types of inherited metabolic disorders, inborn errors of fatty acid oxidation and mitochondrial electron transport chain (ETC) defects. Clinically significant cardiac involvement is also now recognized to be a serious complication, if not the present problem, in patients with some inherited metabolic diseases in which it was previously unknown, rare, or trivial.

Cardiomyopathy

Many of the inherited metabolic disorders in which cardiac disease is particularly prominent present as cardiomyopathy (Table 5.1). The clinical characteristics of the cardiomyopathy itself are often not much help in determining whether it is the result of an inborn error of metabolism or some nonmetabolic condition, such as infection or intoxication. Moreover, even among the inherited metabolic diseases, the clinical characteristics of the cardiac involvement are usually not characteristic enough to suggest a specific diagnosis without further investigation.

In most inherited metabolic diseases presenting with cardiomyopathy, echocardiography shows some thickening of the left ventricular wall. However, in some, notably in patients with systemic carnitine deficiency, the marked enlargement of the heart seen on radiographs of the chest is principally the result of dilatation. Cardiac enlargement and dilatation is commonly accompanied by arrhythmias.