Cardiac involvement in carriers of Duchenne and Becker muscular dystrophy

Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule

The severe Duchenne and milder Becker muscular dystrophy are both caused by mutations in the DMD gene. This gene codes for dystrophin, a protein important for maintaining the stability of muscle-fiber membranes. In 1988, Monaco and colleagues postulated an explanation for the phenotypic difference between Duchenne and Becker patients in the reading-frame rule: In Duchenne patients, mutations induce a shift in the reading frame leading to prematurely truncated, dysfunctional dystrophins. In Becker patients, in-frame mutations allow the synthesis of internally deleted, but largely functional dystrophins. Currently, over 4700 mutations have been reported in the Leiden DMD mutation database, of which 91% are in agreement with this rule. In this study we provide an update of the mutational variability in the DMD gene, particularly focusing on genotype-phenotype correlations and mutations that appear to be exceptions to the reading-frame rule.

Long-term administration of pirfenidone improves cardiac function inmdx mice

Duchenne muscular dystrophy, an X-linked recessive neuromuscular disorder due to lack of the protein dystrophin, manifests as progressive muscle degeneration and cardiomyopathy with increased fibrosis. The exact mechanisms involved in fibrosis are unknown, but a cytokine, transforming growth factor-beta (TGF-beta), is a likely mediator. This study tested whether the TGF-beta antagonist, pirfenidone, could reduce cardiac fibrosis. Eight-month-old mdx mice were treated for 7 months with 0.4%, 0.8%, and 1.2% pirfenidone in drinking water; untreated water was given to control mdx and C57 mice. Mice treated with 0.8% and 1.2% pirfendone had lowered cardiac TGF-beta mRNA and improved in vitro cardiac contractility (P < 0.05) to levels consistent with C57 mice, yet without a change in cardiac stiffness or fibrosis. These results show that the TGF-beta antagonist, pirfenidone, can improve cardiac function in mdx mice, potentially providing a new avenue for developing cardiac therapies for patients with Duchenne muscular dystrophy.

Cardiovascular health supervision for individuals affected by Duchenne or Becker muscular dystrophy

Duchenne muscular dystrophy is the most common and severe form of the childhood muscular dystrophies. The disease is typically diagnosed between 3 and 7 years of age and follows a predictable clinical course marked by progressive skeletal muscle weakness with loss of ambulation by 12 years of age. Death occurs in early adulthood secondary to respiratory or cardiac failure. Becker muscular dystrophy is less common and has a milder clinical course but also results in respiratory and cardiac failure. The natural history of the cardiomyopathy in these diseases has not been well established. As a result, patients traditionally present for cardiac evaluation only after clinical symptoms become evident. The purpose of this policy statement is to provide recommendations for optimal cardiovascular evaluation to health care specialists caring for individuals in whom the diagnosis of Duchenne or Becker muscular dystrophy has been confirmed.

[Cardiac manifestations of muscular dystrophies]

Muscular dystrophies (MD) are a clinically and genetically heterogeneous disease group. In the last few years, remarkable progress has been made in understanding the close und various relations between skeletal muscle disease and heart muscle disease. Cardiac involvement has been documented in a number of primary MDs and is even the dominant feature in some of them. The myocardium can be affected in the form of a dilated cardiomyopathy while the conduction system can be affected resulting in arrhythmias and conduction defects. Many patients with MD die because of cardiac complications like sudden cardiac death or congestive heart failure. Detailed clinical data about cardiac involvement are available for Duchenne/Becker MD, Emery-Dreifuss MD, myotonic dystrophy, and the different limb girdle MDs. Cardiac manifestations were also found in congenital MD, central core disease, proximal myotonic myopathy, and nemaline myopathy. No data about cardiac abnormalities are available in oculopharyngeal MD and rippling muscle disease. The heart of patients with primary MD should be carefully investigated because of the life-threatening events caused by cardiac complications. There is a strong need for a close collaboration between neurologists and cardiologists in order to provide optimal disease management for the affected patients.

Occult Cardiac Contractile Dysfunction in Dystrophin-Deficient Children Revealed by Cardiac Magnetic Resonance Strain Imaging

Background— Duchenne muscular dystrophy (DMD) is an inherited disease characterized by early onset of skeletal muscle degeneration and progressive weakness. Although dilated cardiomyopathy may occur during adolescence, it is often undetected early in its course because of physical inactivity and generalized debilitation. The purpose of this study was to apply the technique of cardiac magnetic resonance (CMR) tagging to detect occult cardiac dysfunction in young subjects with DMD by measuring myocardial strain and torsion.

Methods and Results— Thirteen DMD pediatric subjects without clinically apparent heart disease and 9 age-matched healthy males were recruited. Each was scanned on a 1.5-T clinical scanner to acquire contiguous short-axis planes from the apex to the mitral valve plane and then 3 tagged images at base, midventricle, and apex. Global and segmental myocardial net twist and circumferential strain were computed with the use of 2D homogeneous strain analysis. Ventricular torsion was computed by normalizing net twist by the distance from apex to mitral valve plane. DMD patients exhibited normal left ventricular volumes and ejection fractions but manifested reduced midventricular and basal cross-sectional global circumferential strain compared with the reference group ( P <0.005). These alterations also appeared in segmental analyses in the septal, anterior, lateral, and inferior walls ( P <0.05).

Conclusions— In patients predisposed to cardiomyopathies because of dystrophinopathy, occult regional cardiac dysfunction can be diagnosed with CMR tagging. This method of strain imaging analysis may offer a sensitive approach for delineating the presence and progression of cardiovascular disease and for assessing therapies designed to modulate the onset and course of heart failure.

Cardiomyopathy in dystrophin-deficient hearts is prevented by expression of a neuronal nitric oxide synthase transgene in the myocardium

Null mutation of dystrophin causes the lethal pathology of Duchenne muscular dystrophy (DMD) in which there is progressive pathology of skeletal and cardiac muscles. A large proportion of DMD patient deaths are attributable to cardiac dysfunction associated with ventricular fibrosis, arrhythmias and conduction abnormalities, although the relationships between the dystrophin mutation and the cardiac defects are unknown. Here, we tested whether cardiac pathology in dystrophin-deficient mdx mice can be corrected by the elevated production of nitric oxide (NO) by the myocardium. Dystrophin-deficient mdx mice were produced in which there was myocardial expression of a neuronal nitric oxide synthase (nNOS) transgene. Expression of the transgene prevented the progressive ventricular fibrosis of mdx mice and greatly reduced myocarditis. Electrocardiographs (ECG) attained by radiotelemetry of freely ambulatory mice showed that mdx mice displayed cardiac abnormalities that are characteristic of DMD patients, including deep Q-waves, diminished S:R ratios, polyphasic R-waves and frequent premature ventricular contractions. All of these ECG abnormalities in mdx mice were improved or corrected by nNOS transgene expression. In addition, defects in mdx cardiac autonomic function, which were reflected by decreased heart rate variability, were significantly reduced by nNOS transgene expression. These findings indicate that increasing NO production by dystrophic hearts may have therapeutic value.

Complications of anaesthesia in neuromuscular disorders

The purpose of this review is to alert non-anaesthesiologists to the various complications from which patients with neuromuscular disorders and those susceptible to malignant hyperthermia can suffer during anaesthesia. The patient's outcome correlates with the quality of consultation between anaesthesiologists, surgeons, neurologists and cardiologists. Special precautions must be taken, since many anaesthetics and muscle relaxants can aggravate the clinical features or trigger life-threatening reactions. Complications frequently occur in these patients, although anaesthetic procedures have become safer by the reduced administration of suxamethonium and the use of total intravenous anaesthesia, new volatile anaesthetics and non-depolarising relaxants. This review provides a synopsis of pre-operative anaesthetic considerations and adverse drug effects on skeletal, cardiac and smooth muscle tissue. It describes the pathogenetic aspects of typical complications and introduces anaesthetic procedures for the various neuromuscular disorders, including regional anaesthesia for patients in whom a restriction of respiratory and/or cardiac function is predicted.

Cardiac complications of childhood myopathies

The management of individuals with a neuromuscular disorder is usually focused on the skeletal muscle weakness and resulting complications, such as respiratory failure. Long-term prognosis of a number of neuromuscular conditions is, however, also determined by the type and severity of cardiac involvement. Early recognition and treatment of the cardiovascular complications are part of the task of the multidisciplinary team involved in the care of these patients. Although for several of the common conditions, there is general consensus on the cardiac investigations and treatments, in the rarer disorders, evidence-based recommendations are not available, and suggestions from experts provide an acceptable solution. This review summarizes the recent advances in our understanding of the pathogenesis and phenotypic diversity of cardiac complications associated with pediatric myopathies and provides a rational framework for planning the monitoring and therapeutic intervention in individual conditions.

Cardiac assessment in childhood carriers of Duchenne and Becker muscular dystrophies

Cardiac disease in adult female carriers of the X-linked dystrophinopathies, Duchenne and Becker muscular dystrophies, is a well-recognised entity. A single study has reported a 15% incidence of cardiac abnormalities in female carriers under 16 years. Our study aims, clinically and with electrocardiograph and echocardiograph, to determine the incidence of cardiac abnormality in young girls who are proven carriers of X-linked dystrophinopathies. Twenty-three girls aged 6.2-15.9 years were assessed. All had normal cardiac examination. None had electrocardiograph abnormalities consistent with dystrophic cardiomyopathy. Left ventricular fractional shortening ranged from 33 to 55% (normal>28%). Septal thickness, posterior wall thickness and wall thickness ratio were within normal limits. No cardiac abnormalities have been demonstrated in young girls who are proven carriers of X-linked dystrophinopathies in our study. This has important implications for planning timing of carrier determination and cardiac assessment.

Cardiac abnormalities and skeletal muscle weakness in carriers of Duchenne and Becker muscular dystrophies and controls

Cardiac abnormalities, cardiomyopathy and skeletal muscle weakness have been described in female carriers of the Xp21 (Duchenne and Becker) muscular dystrophies (J Neurol 1975;209(4):279-285; Br Med J 1969;2:418-420; J AmMed Assoc 1996;275(17):1335-1338; Neurology 1980;30(5):497-501; Neuromusc Disord 1999;9:347-351; Arch Neurol 1989;46:673-675). We have screened volunteers from our Xp21 genetics register and found the prevalence of previously unrecognized, clinically relevant, abnormalities in this group to be less than previously reported. We studied 91 women (56 carriers and 35 controls), aged between 18 and 69 years, from our local population known to the Oxford Regional Genetics Register. Our study included controls, with the investigators being blind to the subject's genetic status. The prevalence of previously unrecognised cardiac abnormalities on echocardiogram and ECG was 18% (10/56). Seven percent (4/56) of carriers had cardiomyopathy, defined by significant LV dilatation and decreased shortening fraction. In most cases, subjects with abnormal cardiac findings were asymptomatic. Echocardiography was more frequently abnormal than electrocardiography, but in many subjects the measurements of left ventricular dimensions were only just outside the normal ranges. The prevalence of skeletal muscle weakness was 12% (7/56). It was usually recognized by the individual, although not previously volunteered, but was mild and did not substantially affect activities of daily living.