Metabolic and genetic investigations of cardiomyopathy in childhood.

Metabolic cardiomyopathy of babies and children accounts for approximately 15% of all cardiomyopathies presenting at these ages. The confirmation of t he aetiology is essential for treatment, which is rarely curative. For esta blishing a prognosis which is often poor, and, above all, for family counse lling in cases of mendelian transmission or mitochondrial disease. Cardiomyopathy due to glycogen (Pompe's disease) or mucopolysaccharide (Hur ler's disease) disorders are easy to diagnose because of obvious extracardi ac manifestations. The diagnosis of the enzyme deficiency only requires a b lood and/or urine test. Cardiomyopathies due to a deficit of oxidative metabolism are usually assoc iated with multi-system abnormalities but may be isolated or the presenting sign of the deficit. The diagnosis should be suspected in cases of a posit ive family history of cardiomyopathy or sudden death, of co-sanguinity, of unusual or unexplained extracardiac disease, of atypical ECG changes or of hypoglycaemia. Chromatography of organic acids, analysis of acylcarnitines and -oxidation of the fatty acid oxidation. Of these conditions, only prima ry carnitine deficits are curable. The diagnosis of mitochondrial cardiomyopathy is based on the ratios of oxi doreduction and, above all, on spectrophotometric analysis of the respirato ry chain complexes in skeletal or cardiac muscle (when the heart is the onl y organ involved). Genetic counselling is difficult and punctual mutations or deletions of mitochondrial DNA are rarely observed, and also few nuclear genes coding for the proteins of the respiratory chain have been identifie d to this day.