Natural history of cardiac involvement in myotonic dystrophy (Steinert's disease): a 13-year follow-up study

Cardiac Pathology in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1), the most common muscular dystrophy affecting adults and children, is a multi-systemic disorder affecting skeletal, cardiac, and smooth muscles as well as neurologic, endocrine and other systems. This review is on the cardiac pathology associated with DM1. The heart is one of the primary organs affected in DM1. Cardiac conduction defects are seen in up to 75% of adult DM1 cases and sudden death due to cardiac arrhythmias is one of the most common causes of death in DM1. Unfortunately, the pathogenesis of cardiac manifestations in DM1 is ill defined. In this review, we provide an overview of the history of cardiac studies in DM1, clinical manifestations, and pathology of the heart in DM1. This is followed by a discussion of emerging data about the utility of cardiac magnetic resonance imaging (CMR) as a biomarker for cardiac disease in DM1, and ends with a discussion on models of cardiac RNA toxicity in DM1 and recent clinical guidelines for cardiologic management of individuals with DM1.

Variability of multisystemic features in myotonic dystrophy type 1--lessons from Serbian registry

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a rare disease. Creating registry for such a disease is of outstanding importance since it provides us with a full spectrum of the disorder.

AIM

To assess variability of different multisystemic features in a large cohort of patients with DM1.

PATIENTS AND METHOD

Data from the Serbian registry for myotonic dystrophies were used in the study. Final number of included DM1 subjects was 275.

RESULTS

Registry included 53.8% of male patients. Age at enrollment was 47.2 ± 9.9 years, mean disease duration 20.4 ± 9.9 years, and mean CTG repeats number 598.3 ± 269.8.Progression of muscle weakness was pretty slow, slower in proximal than distal muscles, and slower in arms than in legs. Severe ECG abnormality was found in 25.0% of patients and pacemaker was implanted in 9.5%. Lens opacities were observed in 83.5% of DM1 patients and 35.3% had ocular hypotony. Metabolic disturbances were very common, while 19.5% of patients had hypokalemia and 37.8% hypochloremia. Sterility was found in 20.5% of males and 4.1% of females. Cholelithiasis was found in 36.4% of patients and constipation in 29.9%.

CONCLUSIONS

We defined the most common characteristics of our DM1 patients and observed some treatable symptoms that have been neglected previously. Certain findings deserve further investigations in terms of their causes and consequences. Besides this, presented data analysis directs us to make further improvements of the registry.

Muscle wasting in myotonic dystrophies: a model of premature aging

Myotonic dystrophy type 1 (DM1 or Steinert’s disease) and type 2 (DM2) are multisystem disorders of genetic origin. Progressive muscular weakness, atrophy and myotonia are the most prominent neuromuscular features of these diseases, while other clinical manifestations such as cardiomyopathy, insulin resistance and cataracts are also common. From a clinical perspective, most DM symptoms are interpreted as a result of an accelerated aging (cataracts, muscular weakness and atrophy, cognitive decline, metabolic dysfunction, etc.), including an increased risk of developing tumors. From this point of view, DM1 could be described as a progeroid syndrome since a notable age-dependent dysfunction of all systems occurs. The underlying molecular disorder in DM1 consists of the existence of a pathological (CTG) triplet expansion in the 3′ untranslated region (UTR) of the Dystrophia Myotonica Protein Kinase (DMPK) gene, whereas (CCTG)n repeats in the first intron of the Cellular Nucleic acid Binding Protein/Zinc Finger Protein 9(CNBP/ZNF9) gene cause DM2. The expansions are transcribed into (CUG)n and (CCUG)n-containing RNA, respectively, which form secondary structures and sequester RNA-binding proteins, such as the splicing factor muscleblind-like protein (MBNL), forming nuclear aggregates known as foci. Other splicing factors, such as CUGBP, are also disrupted, leading to a spliceopathy of a large number of downstream genes linked to the clinical features of these diseases. Skeletal muscle regeneration relies on muscle progenitor cells, known as satellite cells, which are activated after muscle damage, and which proliferate and differentiate to muscle cells, thus regenerating the damaged tissue. Satellite cell dysfunction seems to be a common feature of both age-dependent muscle degeneration (sarcopenia) and muscle wasting in DM and other muscle degenerative diseases. This review aims to describe the cellular, molecular and macrostructural processes involved in the muscular degeneration seen in DM patients, highlighting the similarities found with muscle aging.

Structural myocardial involvement in adult patients with type 1 myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is the commonest muscular dystrophy in adults, affecting multiple organs in addition to skeletal muscles. Cardiac conduction system abnormalities are well recognized as an important component of DM1 phenotype; however, primary structural myocardial abnormalities, which may predispose these patients to congestive heart failure, are not as well characterized. We reviewed the retrospective analysis of the clinical and echocardiographic findings in adult patients with DM1. Among 27 patients (16 male; age 19–61 years) with DM1, the echocardiogram (ECHAO) was abnormal in 10 (37%) including one of 6 patients (16%) with congenital myotonic dystrophy. Reduced left ventricular ejection fraction (LVEF ≤50%) was noted in 5, diastolic dysfunction in 4, left atrial dilatation in 3, left ventricular hypertrophy in 2, apical hypokinesia in 1 and mitral valve prolapse in 3 patients. One patient had paradoxical septal movement in the setting of left bundle branch block. Echocardiographic abnormalities significantly correlated with older age; however, patients with systolic dysfunction on echocardiogram ranged in age from 27 to 52 years including 2 patients aged 27 and 34 years. We can conclude that echocardiographic abnormalities are frequent in adult patients with DM1. The incidence is similar in the classical and congenital type of DM1. Overall, echocardiographic abnormalities in DM1 correlate with increasing age; however, reduced LVEF is observed even at young age. Cardiac assessment and monitoring in adult patients with DM1 should include evaluation for primary myocardial involvement.

[Heart and Steinert's disease]

Myotonic dystrophy type 1 (Steinert disease) is an autosomal dominant disease characterized by myotonia and multiorgan damage. This latter is the most frequent of the adult-onset muscular dystrophies. Heart involvement is often associated, including cardiomyopathies, atrioventricular block, atrial and ventricular arrhythmias.

Evaluation of biventricular functions with tissue Doppler imaging in patients with myotonic dystrophy

BACKGROUND

Myotonic dystrophy (MD) is characterized by myotonia with dystrophic involvement of the muscles. Cardiac involvement is usually not evident in the early stages of MD.

HYPOTHESIS

We investigated biventricular functions by tissue Doppler imaging (TDI) in MD patients with no overt cardiac involvement to explore the value of TDI in the early detection of myocardial dysfunction.

METHODS

A total of 21 MD patients (15 male, age: 32.2 +/- 12.3 yrs) and 21 healthy controls (13 male, age: 32.2 +/- 7.8 yrs) were included. In addition to conventional echocardiography, pulsed Doppler and TDI were performed including measurement of myocardial performance index (MPI); peak systolic (Sm) and early (Em) and atrial (Am) diastolic myocardial velocities at the basal mitral and tricuspid annulus.

RESULTS

All patients and controls had normal ejection fraction. Transmitral E peak velocity was significantly lower while both deceleration time of E velocity and isovolumic relaxation time were significantly longer in MD patients (P = 0.007, P = 0.001, and P < 0.001, respectively). Sm, Em and Am peak velocities were significantly lower in MD patients in all segments except for Em of the mitral anterior annulus and Am of the tricuspid lateral annulus. Both left and right ventricular MPI were significantly higher in MD patients (P < 0.001 and P = 0.013, respectively).

CONCLUSION

There are changes in myocardial systolic and diastolic functions in MD patients although they have no overt heart failure. Myocardial tissue velocities and MPI are useful in identifying subclinical biventricular involvement in these patients.

Usefulness of clinical and electrocardiographic data for predicting adverse cardiac events in patients with myotonic dystrophy

BACKGROUND

Myotonic dystrophy type 1 (DM1) has been associated with an increased risk of sudden death, either by heart block or malignant ventricular arrhythmias. Identifying patients at risk remains difficult and no consensus has been reached regarding the best approach for follow-up and prevention of sudden death.

OBJECTIVES

To identify noninvasive clinical and electrocardiographic predictors of adverse cardiac events in patients with DM1.

METHODS

Clinical and serial electrocardiographic data on 428 patients with a DNA-proven diagnosis of DM1, followed during a mean period of 11.7 years, were reviewed. Variables associated with adverse cardiac events were identified.

RESULTS

Eleven patients (2.6%) experienced sudden death and 13 (3.0%) required implantation of a pacemaker. On univariate analysis, adverse events were associated with advancing age, prolongation of the PR, QRS and corrected QT (QTc) intervals, as well as the degree of neuromuscular impairment. No such relationship was found with the extent of genetic anomaly (number of cytosine-thymine-guanine repeats). However, multivariate analysis using Cox proportional hazards models showed that only baseline PR and QTc intervals were significantly linked to the end points of sudden death or pacemaker implantation; the age-adjusted RR was 3.7 (95% CI 1.5 to 8.6) if baseline PR was 200 ms or longer (P=0.003), and 3.0 (95% CI 1.0 to 8.8) if the baseline QTc was 450 ms or longer (P=0.047).

CONCLUSIONS

In a large unselected cohort of 428 patients with DM1, the cumulative incidence of sudden death was relatively low, and the delayed conduction on surface electrocardiogram was found to be potentially helpful for identifying patients at risk for sudden death or pacemaker implantation.

Cardiovascular manifestations of myotonic dystrophy-1

Myotonic dystrophy (DM) is an inherited disorder transmitted in an autosomal dominant fashion and characterized by myotonia with dystrophic involvement of muscles and other multisystemic manifestations. It is the most common muscular dystrophy in whites. DM1, the most common type of DM, is associated with conduction defects, tachyarrhythmia, cardiomyopathy, and other cardiac disorders such as valvular diseases. The conduction defects in patients with DM1 are progressive; therefore, these patients should undergo careful work-up and follow-up, even if presenting with a benign conduction defect such as first-degree atrioventricular block. Atrial tachyarrhythmias are the most common arrhythmias in DM1, although ventricular tachycardia (VT) with a bundle branch re-entry mechanism can also occur. Interestingly, such VT can be cured by right bundle branch ablation with no need for an implantable cardioverter defibrillator. A significant portion of DM1 patients have heart failure, which is not clinically apparent, in part, because of the limited ability for exertion. Therefore, a low threshold should be used regarding when evaluating the heart by echocardiogram. Cardiovascular manifestations of DM1 have several important aspects that require careful attention and knowledge of the current evidence to make the best treatment decision. This article reviews the relevant DM1 literature and provides suggestions for diagnosis and treatment of patients with DM1.

Subclinical cardiac involvement in myotonic dystrophy manifesting as decreased myocardial Doppler velocities

To assess subendocardial (long-axis) and mid-wall (short-axis) left ventricular (LV) function in patients with type 1 myotonic dystrophy (MD1), with no symptoms or clinical signs of heart disease, to investigate if they have subclinical cardiac involvement, 28 subjects (14 with MD1, and 14 age- and sex-matched normals) had conventional and tissue Doppler echocardiography. Myocardial velocities and timings to peak systolic contractions were measured. LV wall thickness, diameters, and ejection fraction were not different between the groups. 4/14 of the MD1 patients (29%) had global diastolic dysfunction. Both long-axis and short-axis systolic and early diastolic myocardial velocities were lower in patients with MD1, whereas time-to-peak myocardial contraction was longer; mean longitudinal systolic velocity was 5.5+/-1.7 cm/s in patients with MD1, compared with 7.8+/-1.3 cm/s in normal subjects (P<0.001) 10/14 of the patients (71%) had reduced longitudinal systolic function. Longitudinal systolic and diastolic velocities were inversely related to the duration of the QRS complex ( r=-0.86 and r=-0.63 respectively, both P<0.01), but they did not correlate with the CTG-repeat size. Patients with MD1 have subclinical cardiac impairment revealed by measurement of myocardial velocities using tissue Doppler echocardiography.

Abnormal contractile activity and calcium cycling in cardiac myocytes isolated from DMPK knockout mice

Dysfunction of the gene encoding DMPK (myotonic dystrophy protein kinase) has been implicated in the human neuromuscular disease myotonic dystrophy (DM1). The cardiac features of the disease include progressive conduction defects and ventricular arrhythmias. These defects have been observed in hearts of mice deficient for DMPK function. We have investigated the role of DMPK in the function of ventricular cardiomyocytes using dmpk knockout (KO) mice. A deficit in DMPK caused enhanced basal contractility of single cardiomyocytes and an associated increase in intracellular Ca(2+), measured using fura-2. Biochemical measurements indicated hyperphosphorylation of phospholamban (PLB) in KO mice. This suggests increased Ca(2+) uptake into the sarcoplasmic reticulum (SR) as the underlying cause of enhanced contractility. This conclusion was supported by the larger amplitude of caffeine-induced Ca(2+) release from the SR in KO cardiomyocytes. Concurrent with hyperphosphorylated PLB, the response to isoprenaline was reduced. These observations suggest dmpk has a modulatory role in the control of intracellular Ca(2+) concentration in mouse ventricular cardiomyocytes, loss of which may contribute to cardiac dysfunction in DM1.

Proximal myotonic myopathy: a syndrome with a favourable prognosis?

Cardiac involvement in myotonic dystrophy type 1 (DM1) is well known. In contrast, the severity and frequency of cardiac abnormalities in proximal myotonic myopathy (PROMM) are still unclear. To identify similarities and differences in the rate of progression of muscle weakness and cardiac disturbances in these two disorders, 16 patients with PROMM (3q-unlinked PROMM: n=10; uniformative for linkage: n=6) were compared to 33 patients with moderately severe myotonic dystrophy type 1 (DM1). There was no significant difference in disease duration between PROMM and DM1. Patients underwent serial manual muscle strength testing, EKG, 24-h Holter monitoring, 2D-echocardiography. Muscle weakness progressed slowly in both groups. Most DM1 patients developed conduction defects. No significant atrioventricular disturbances on initial and follow-up examinations were found in PROMM patients. One patient developed right bundle branch block. Many families with PROMM appear to have more benign cardiac manifestations and less severe prognosis compared to DM1. Further studies of subgroups of PROMM (linked to the 3q21 locus and without linkage) are necessary to determine whether the cardiac conduction disturbances are more common in a specific genotype of PROMM.