[Metabolic and genetic investigations in childhood cardiomyopathies].
Metabolic cardiomyopathy of babies and children accounts for approximately 15% of all cardiomyopathies presenting at these ages. The confirmation of the aetiology is essential for treatment, which is rarely curative. For establishing a prognosis which is often poor, and, above all, for family counselling in cases of mendelian transmission or mitochondrial disease. Cardiomyopathy due to glycogen (Pompe's disease) or mucopolysaccharide (Hurler's disease) disorders are easy to diagnose because of obvious extracardiac manifestations. The diagnosis of the enzyme deficiency only requires a blood and/or urine test. Cardiomyopathies due to a deficit of oxidative metabolism are usually associated with multi-system abnormalities but may be isolated or the presenting sign of the deficit. The diagnosis should be suspected in cases of a positive 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 primary carnitine deficits are curable. The diagnosis of mitochondrial cardiomyopathy is based on the ratios of oxidoreduction and, above all, on spectrophotometric analysis of the respiratory chain complexes in skeletal or cardiac muscle (when the heart is the only 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 identified to this day.