Hypertrophic cardiomyopathy in three generations of a large Norwegian family. A clinical, echocardiographic, and genetic study

Cardiomyopathy in childhood, mitochondrial dysfunction, and the role of L-carnitine

Cardiomyopathy in childhood is associated with high morbidity and mortality rates. Many metabolic causes have been identified, including genetic or acquired defects in mitochondrial energy production affecting beta-oxidation, carnitine transport, and the electron transport chain. Combining conventional inotropic and antiarrhythmic therapy with metabolic interventions has improved overall outcome. L-carnitine, a natural substance involved in mitochondrial transport of fatty acids, is one such therapy and plays a central role in the regulation of the inner mitochondrial supply of free coenzyme A. Carnitine deficiency can be caused by both genetic and environmental causes with resultant signs and symptoms of metabolic disease, including cardiomyopathy. Administration of L-carnitine can result in improvement or resolution of the cardiomyopathy.

Sporadic hypertrophic cardiomyopathy due to de novo myosin mutations

Hypertrophic cardiomyopathy occurs as an autosomal dominant familial disorder or as a sporadic disease without familial involvement. While missense mutations in the beta cardiac myosin heavy chain (MHC) gene account for approximately half of all cases of familial hypertrophic cardiomyopathy, the molecular causes of sporadic hypertrophic cardiomyopathy are unknown. To determine whether beta cardiac MHC mutations are also associated with sporadic disease, we screened this gene in seven individuals with sporadic hypertrophic cardiomyopathy. Mutations in the beta cardiac MHC genes were identified in two probands with sporadic disease. In that their parents were neither clinically nor genetically affected, we conclude that mutations in each proband arose de novo. Transmission of the mutation and disease to an offspring occurred in one pedigree, predicting that these are germline mutations. The demonstration of hypertrophic cardiomyopathy arising within a pedigree coincident with the appearance of a de novo mutation provides compelling genetic evidence that beta cardiac MHC mutations cause this disease. We suggest that de novo mutations account for some instances of sporadic hypertrophic cardiomyopathy and that these mutations can be transmitted to children. The clinical benefits of defining mutations responsible for familial hypertrophic cardiomyopathy should also be available to some patients with sporadic disease.

Hypertrophic cardiomyopathy in identical twins

Hypertrophic cardiomyopathy was diagnosed in identical twin boys in early childhood. One underwent myomectomy at the age of 12 years because of progressive severe exertional dyspnoea accompanied by considerable obstruction of the left ventricular outflow tract shown on both echocardiography and cardiac catheterisation. Seven years later, at the age of 19, he remains incapacitated to a moderate degree. By contrast, the other twin has led a relatively normal life to date and no left ventricular outflow obstruction has been shown.

Electrocardiographic changes can precede the development of myocardial hypertrophy in the setting of hypertrophic cardiomyopathy

A comparison was made of electrocardiographic findings in 107 first-degree relatives of patients with hypertrophic cardiomyopathy without any clinical and echocardiographic signs of the disease and 188 healthy persons with a negative family history. A significantly larger number of electrocardiographic signs of left ventricular hypertrophy (P less than 0.05) and abnormal Q wave (P less than 0.005) was shown in the group of the relatives. Abnormalities of the R wave in V1-3 and of the ST-T segment were also more frequent in this group, but the difference is not statistically significant. In all, electrocardiographic abnormalities were found in 13 of 107 asymptomatic relatives of the patients with hypertrophic cardiomyopathy. These relatives had normal clinical and echocardiographic findings. These 13 patients underwent long-term follow-up (4.5-8 years). Typical hypertrophic cardiomyopathy developed in two patients (an increase in the myocardial thickness from 6 to 15 m in six years and from 8 to 13 mm in 4.5 years, respectively) which was accompanied by progression of the electrocardiographic findings. Electrocardiography is the only commonly available method which may reveal the latent forms of hypertrophic cardiomyopathy at the stage when neither myocardial hypertrophy nor other signs of the disease are expressed. Longitudinal follow-up is necessary for all the relatives of the patients with hypertrophic cardiomyopathy who have abnormal or borderline electrocardiographic findings. A normal echocardiogram cannot exclude the disease at this stage.