Cardiomyopathy in the Kearns-Sayre syndrome

Cardiac Involvement in Mitochondrial Disorders

PURPOSE OF REVIEW

We review pathophysiology and clinical features of mitochondrial disorders manifesting with cardiomyopathy.

RECENT FINDINGS

Mechanistic studies have shed light into the underpinnings of mitochondrial disorders, providing novel insights into mitochondrial physiology and identifying new therapeutic targets. Mitochondrial disorders are a group of rare genetic diseases that are caused by mutations in mitochondrial DNA (mtDNA) or in nuclear genes that are essential to mitochondrial function. The clinical picture is extremely heterogeneous, the onset can occur at any age, and virtually, any organ or tissue can be involved. Since the heart relies primarily on mitochondrial oxidative metabolism to fuel contraction and relaxation, cardiac involvement is common in mitochondrial disorders and often represents a major determinant of their prognosis.

Cardiomyopathies in Children and Systemic Disorders When Is It Useful to Look beyond the Heart?

Cardiomyopathy (CMP) is a rare disease in the pediatric population, with a high risk of morbidity and mortality. The genetic etiology of CMPs in children is extremely heterogenous. These two factors play a major role in the difficulties of establishing standard diagnostic and therapeutic protocols. Isolated CMP in children is a frequent finding, mainly caused by sarcomeric gene variants with a detection rate that can reach up to 50% of analyzed cohorts. Complex multisystemic forms of pediatric CMP are even more heterogenous. Few studies in literature take into consideration this topic as the main core since it represents a rarity (systemic CMP) within a rarity (pediatric population CMP). Identifying etiology in this cohort is essential for understanding prognosis, risk stratification, eligibility to heart transplantation and/or mechanical-assisted procedures, preventing multiorgan complications, and relatives' recurrence risk calculation. The previous points represent a cornerstone in patients' empowerment and personalized medical care approach. The aim of this work is to propose a new approach for an algorithm in the setting of the diagnostic framework of systemic pediatric CMP. On the other hand, during the literature review, we noticed a relatively common etiologic pattern in some forms of complex/multisystem CMP. In other words, certain syndromes such as Danon, Vici, Alström, Barth, and Myhre syndrome share a common pathway of directly or indirectly defective "autophagy" process, which appears to be a possible initiating/triggering factor for CMPs. This conjoint aspect could be important for possible prognostic/therapeutic implications in this category of patients. However, multicentric studies detailed functional and experimental models are needed prior to deriving conclusions.

Generation and Evaluation of Isogenic iPSC as a Source of Cell Replacement Therapies in Patients with Kearns Sayre Syndrome

Kearns Sayre syndrome (KSS) is mitochondrial multisystem disorder with no proven effective treatment. The underlying cause for multisystem involvement is the energy deficit resulting from the load of mutant mitochondrial DNA (mtDNA), which manifests as loss of cells and tissue dysfunction. Therefore, functional organ or cellular replacement provides a promising avenue as a therapeutic option. Patient-specific induced pluripotent stem cells (iPSC) have become a handy tool to create personalized cell -based therapies. iPSC are capable of self-renewal, differentiation into all types of body cells including cardiomyocytes (CM) and neural progenitor cells (NPC). In KSS patients, mutations in mtDNA are largely found in the muscle tissue and are predominantly absent in the blood cells. Therefore, we conceptualized that peripheral blood mononuclear cells (PBMNC) from KSS patients can be reprogrammed to generate mutation free, patient specific iPSC lines that can be used as isogenic source of cell replacement therapies to treat affected organs. In the current study we generated iPSC lines from two female patients with clinical diagnosis of classic KSS. Our data demonstrate that iPSC from these KSS patients showed normal differentiation potential toward CM, NPC and fibroblasts without any mtDNA deletions over passages. Next, we also found that functional studies including ATP production, reactive oxygen species generation, lactate accumulation and mitochondrial membrane potential in iPSC, CM, NPC and fibroblasts of these KSS patients were not different from respective cells from healthy controls. PBMNCs from these KSS patients in the current study did not reproduce mtDNA mutations which were present in muscle biopsies. Furthermore, we demonstrate for the first time that this phenomenon provides opportunities to create isogenic mutation free iPSC with absent or very low level of expression of mtDNA deletion which can be banked for future cell replacement therapies in these patients as the disease progresses.

Cardiomyopathies Due to Left Ventricular Noncompaction, Mitochondrial and Storage Diseases, and Inborn Errors of Metabolism

The normal function of the human myocardium requires the proper generation and utilization of energy and relies on a series of complex metabolic processes to achieve this normal function. When metabolic processes fail to work properly or effectively, heart muscle dysfunction can occur with or without accompanying functional abnormalities of other organ systems, particularly skeletal muscle. These metabolic derangements can result in structural, functional, and infiltrative deficiencies of the heart muscle. Mitochondrial and enzyme defects predominate as disease-related etiologies. In this review, left ventricular noncompaction cardiomyopathy, which is often caused by mutations in sarcomere and cytoskeletal proteins and is also associated with metabolic abnormalities, is discussed. In addition, cardiomyopathies resulting from mitochondrial dysfunction, metabolic abnormalities, storage diseases, and inborn errors of metabolism are described.

Solid organ transplantation in primary mitochondrial disease: Proceed with caution

Solid organ transplants are rarely performed in both adult and pediatric patients with primary mitochondrial disease. Poor outcomes have been described in case reports and small case series. It is unclear whether the underlying genetic disease has a significant impact on post-transplant morbidity and mortality. Data were obtained for 35 patients from 17 Mitochondrial Disease Centers across North America, the United Kingdom and Australia. Patient outcomes were noted after liver, kidney or heart transplantation. Excluding patients with POLG-related disease, post-transplant survival approached or met outcomes seen in non-mitochondrial disease transplant patients. The majority of mitochondrial disease patients did not have worsening of their mitochondrial disease within 90-days post-transplant. Post-transplant complications, including organ rejection, were not a common occurrence and were generally treatable. Many patients did not have a mitochondrial disease considered or diagnosed prior to transplantation. In conclusion, patients with mitochondrial disease in this cohort generally tolerated solid-organ transplantation. Such patients may not need to be excluded from transplant solely for their mitochondrial diagnosis; additional caution may be needed for patients with POLG-related disease. Transplant teams should be aware of mitochondrial disease as an etiology for organ-failure and consider appropriate consultation in patients without a known cause of their symptoms.

Dilated cardiomyopathy with cardiogenic shock in a child with Kearns-Sayre syndrome

Kearns-Sayre syndrome (KSS) is a mitochondrial myopathy resulting from mitochondrial DNA deletion. This syndrome primarily involves the central nervous system, eyes, skeletal muscles and the heart. The most well-known cardiac complications involve the conduction system; however, there have been case reports describing cardiomyopathy. We describe a case of a child with KSS who presented with decompensated cardiac failure from dilated cardiomyopathy representing cardiomyocyte involvement of KSS. Our patient had a rapidly progressing course, despite maximal medical management, requiring emergent institution of extracorporeal membrane oxygenation and transition to a ventricular assist device. To the best of our knowledge, this is the youngest patient in the literature to have dilated cardiomyopathy in KSS.

Cardiac involvement in hereditary ataxias

Although much attention has been focused on the neurological sequelae of the hereditary ataxias, patients with these conditions also may develop cardiac complications that represent a significant cause of disability and even death. In this article, the authors describe the hereditary ataxias with known cardiac involvement, discuss underlying causes, and review guidelines for screening and treatment. Continued progress will require coordinated clinical trial networks, interdisciplinary care teams, and team science.

Cardiovascular magnetic resonance imaging (CMR) reveals characteristic pattern of myocardial damage in patients with mitochondrial myopathy

BACKGROUND

Mitochondrial myopathy comprises various clinical subforms of neuromuscular disorders that are characterised by impaired mitochondrial energy metabolism due to dysfunction of the mitochondrial respiratory chain. No comprehensive and targeted cardiovascular magnetic resonance (CMR) studies have been performed so far in patients with mitochondrial disorders. The present study aimed at characterising cardiac disease manifestations in patients with mitochondrial myopathy and elucidating the in vivo cardiac damage pattern of patients with different subforms of mitochondrial disease by CMR studies.

METHODS AND RESULTS

In a prospective study, 37 patients with mitochondrial myopathy underwent comprehensive neurological and cardiac evaluations including physical examination, resting ECG and CMR. The CMR studies comprised cine-CMR, T2-weighted "edema" imaging and T1-weighted late-gadolinium-enhancement (LGE) imaging. Various patterns and degrees of skeletal myopathy were present in the participants of this study, whereas clinical symptoms such as chest pain symptoms (in eight (22%) patients) and various degrees of dyspnea (in 16 (43%) patients) were less frequent. Pathological ECG findings were documented in eight (22%) patients. T2-weighted "edema" imaging was positive in one (3%) patient with MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes) only. LGE imaging demonstrated the presence of non-ischemic LGE in 12 (32%) patients: 10 out of 24 (42%) patients with CPEO (chronic progressive external ophthalmoplegia) or KSS (Kearns-Sayre syndrome) and 2 of 3 (67%) patients with MELAS were LGE positive. All 10 LGE-positive patients with CPEO or KSS demonstrated a potentially typical pattern of diffuse intramural LGE in the left-ventricular (LV) inferolateral segments.

CONCLUSIONS

Cardiac involvement is a frequent finding in patients with mitochondrial myopathy. A potentially characteristic pattern of diffuse intramural LGE in the LV inferolateral segments was identified in patients suffering from the subforms CPEO or KSS.

The molecular genetics of arrhythmias and sudden death

The current status of the research in genetics of cardiac diseases causing sudden death is reviewed. Few techniques will impact medicine as will those of molecular biology. The identification of the gene-causing diseases will allow the use of better preventive, diagnostic, and therapeutic options. From genetic counseling at present to gene therapy in the future, the new challenge for the clinician will be to acquire the new information provided by molecular biology and apply it at the bedside to improve the quality of life for the patient.

Cardiac dysfunction in patients with chronic progressive external ophthalmoplegia

BACKGROUND

Chronic progressive external ophthalmoplegia (CPEO), which includes Kearns-Sayre syndrome, is a mitochondrial disorder with large deletions of mitochondrial DNA. Recently, mtDNA deletions in cardiac muscle cells were thought to be a cause of dilated cardiomyopathy. However, the cardiac involvement in patients with CPEO is generally considered to be limited to the cardiac conduction system.

HYPOTHESIS

The purpose of this study was to evaluate left ventricular function in patients with CPEO.

METHODS

We evaluated the cardiac function of five patients with CPEO by means of carotid pulse recording and Doppler echocardiography.

RESULTS

The ratio of the pre-ejection period to ejection time was increased to 0.67 in one patient and to 0.50 in another. Echocardiography showed left ventricular dilatation and diffuse hypokinetic wall motion in both cases. Left ventricular fractional shortening was decreased to 5 and 19%, respectively, and the mean rate of circumferential shortening was decreased to 0.12 and 0.63 circ/s, respectively. One of the two patient died of congestive heart failure 2 months after the study. The Doppler pattern of left ventricular filling in the three remaining patients showed a decrease in the ratio of peak flow velocity in early diastole to that in late diastole, with an increase in deceleration time.

CONCLUSION

Although cardiac involvement in patients with CPEO is generally considered to be limited to the cardiac conduction system, left ventricular dysfunction may be present and should receive more attention in the management of patients with CPEO.

Continuous venovenous hemodiafiltration for life-threatening mitochondrial myopathy with lactic acidosis and rhabdomyolysis

We report here the clinical course of a 31-year-old male who recovered from a fulminant form of mitochondrial myopathy with lactic acidosis. The patient was transferred to our hospital with acute dyspnea and a convulsive seizure. On admission, he was in a state of shock, and presented with severe high-output heart failure, acute renal failure, and rhabdomyolysis. Treatment with continuous venovenous hemodiafiltration (CVVHDF) resulted in an excellent response, with no signs of hemodynamic instability. This case suggests that CVVHDF with serial hemodynamic monitoring may be effective in treating hypotensive patients with a life-threatening mitochondrial disorder.

Cardiac hypertrophy: mechanisms and therapeutic opportunities

Cardiac hypertrophy and heart failure are major causes of morbidity and mortality in Western societies. Many factors have been implicated in cardiac remodeling, including alterations in gene expression in myocytes, cardiomyocytes apoptosis, cytokines and growth factors that influence cardiac dynamics, and deficits in energy metabolism as well as alterations in cardiac extracellular matrix composition. Many therapeutic means have been shown to prevent or reverse cardiac hypertrophy. New concepts for characterizing the pathophysiology of cardiac hypertrophy have been drawn from various aspects, including medical therapy and gene therapy, or use of stem cells for tissue regeneration. In this review, we focus on various types of cardiac hypertrophy, defining the causes of hypertrophy, describing available animal models of hypertrophy, discussing the mechanisms for development of hypertrophy and its transition to heart failure, and presenting the potential use of novel promising therapeutic strategies derived from new advances in basic scientific research.

The anesthetic management of ventricular septal defect (VSD) repair in a child with mitochondrial cytopathy

PURPOSE

To present the anesthetic management for the correction of a ventricular septal defect (VSD) in a patient with multiple acyl CoA dehydrogenase deficiency (glutaric aciduria type II; GAII). A review of the literature about anesthetic management of patients with mitochondrial diseases undergoing cardiopulmonary bypass (CPB) is also included.

CLINICAL FEATURES

An 11-yr-old girl with GAII manifested as severe hypoglycemia since she was a newborn and generalized muscle weakness. She underwent open-heart surgery for VSD correction with CPB. The anesthetic management avoided inhalational anesthetics, maintained the blood sugar within normal limits and continued normothermia during CPB in order to avoid the stress of hypothermia for her abnormal mitochondria. The patient tolerated the procedure well and experienced a good recovery.

CONCLUSION

The anesthetic management of patients with any mitochondrial disease requires normoglycemia, normothermia and the avoidance of metabolic stress in order to preserve energy production by the diseased mitochondria.

Cardiac abnormalities in patients with mitochondrial DNA mutation 3243A>G

BACKGROUND

Tissues that depend on aerobic energy metabolism suffer most in diseases caused by mutations in mitochondrial DNA (mtDNA). Cardiac abnormalities have been described in many cases, but their frequency and clinical spectrum among patients with mtDNA mutations is unknown.

METHODS

Thirty-nine patients with the 3243A>G mtDNA mutation were examined, methods used included clinical evaluation, electrocardiogram, Holter recording and echocardiography. Autopsy reports on 17 deceased subjects were also reviewed. The degree of 3243A>G mutation heteroplasmy was determined using an Apa I restriction fragment analysis. Better hearing level (BEHL0.5-4 kHz) was used as a measure of the clinical severity of disease.

RESULTS

Left ventricular hypertrophy (LVH) was diagnosed in 19 patients (56%) by echocardiography and in six controls (15%) giving an odds ratio of 7.5 (95% confidence interval; 1.74-67). The dimensions of the left ventricle suggested a concentric hypertrophy. Left ventricular systolic or diastolic dysfunction was observed in 11 patients. Holter recording revealed frequent ventricular extrasystoles (>10/h) in five patients. Patients with LVH differed significantly from those without LVH in BEHL0.5-4 kHz, whereas the contribution of age or the degree of the mutant heteroplasmy in skeletal muscle to the risk of LVH was less remarkable.

CONCLUSIONS

Structural and functional abnormalities of the heart were common in patients with 3243A>G. The risk of LVH was related to the clinical severity of the phenotype, and to a lesser degree to age, suggesting that patients presenting with any symptoms from the mutation should also be evaluated for cardiac abnormalities.

Pearson marrow-pancreas syndrome with worsening cardiac function caused by pleiotropic rearrangement of mitochondrial DNA

Pearson marrow-pancreas syndrome is a usually fatal disorder that involves the hematopoietic system, exocrine pancreas, liver, kidneys, and often presents clinically with failure to thrive. We report a 5-year-old patient who developed, in addition to the typical features of Pearson syndrome, worsening cardiac function, mainly affecting the left ventricle. The latter finding is particularly interesting because cardiac involvement has not yet been regarded as a major feature of Pearson syndrome. The diagnosis was proved by the finding of so far undescribed pleioplasmatic rearrangement of mitochondrial (mt)DNA (loss of 5,630 bp, 70% deleted and duplicated mtDNA) in blood cells. Our report demonstrates that patients with Pearson syndrome may also have impaired cardiac function. Thus, Pearson syndrome should be considered in the differential diagnosis of patients with left ventricular dysfunction of unknown origin and other clinical findings suggestive of a mitochondrial disease.

Mitochondria and the heart

Since the identification of the first pathogenic mutations of mitochondrial DNA in 1988, a plethora of information about human mitochondrial diseases has been brought to light. Not surprisingly, many of these disorders affect the myocardium, because this tissue relies heavily upon oxidative metabolism. This review focuses on disorders of the respiratory chain, the only area of mammalian cellular metabolism under the control of two genomes, nuclear and mitochondrial. Consequently, defects of aerobic synthesis of adenosine triphosphate (ATP) can be due to mutations of either genome. We describe genetic mitochondrial cardiomyopathies and briefly review mouse models and the mitochondrial theory of presbycardia.

Genetic aspects of arrhythmias

Advances in the treatment and prevention of heart disease have led to consistently declining morbidity and mortality rates over the past 30 years. Despite these advances, therapy remains largely palliative. The development of curative therapies is limited by our lack of knowledge of the basic mechanisms of disease. In the next decade, we will probably change many of these current approaches from treating the crisis to preventing the disease. Molecular biology and genetics have elucidated several basic pathways. It is hoped that targeted therapies will prevent or arrest many of these cardiac diseases, in particular, arrhythmias and sudden death. With the discovery of the genes causing familial diseases like long QT, hypertrophic cardiomyopathy, and Brugada syndrome, we have identified several substrates responsible for triggering malignant arrhythmias.

Role of molecular biology in identifying individuals at risk for sudden cardiac death

Cardiology has participated in the new developments in molecular biology and the impact of the Human Genome Project. In these last few years, we have observed how the research in human physiology and journal publications have been focusing on the most basic molecular level. Clinicians have likely been having trouble keeping up with the new developments and, more importantly, with the highly publicized discoveries trying to discern what is research and what can already be applied at the bedside. Molecular biology has just started, and there is no doubt that it will have a tremendous impact in the diagnosis, prevention, and therapy of most diseases, including sudden death and cardiac arrhythmia. In the last few years, we have seen new data in the field of genetics and arrhythmia that are already shaping our approach to an inherited disease. Routine clinical tests are not yet available, mainly due to the lack of sufficiently powerful technology, but with the pace of evolution at this turn of the millennium, we can certainly assume that such testing is just a matter of time.

Genetics of neonatal cardiomyopathy

Cardiomyopathies, primary disorders of the myocardium, are a leading cause of morbidity and mortality in children and adults, and these disorders are responsible for a significant percentage of sudden cardiac deaths and cardiac transplants. Neonatal cardiomyopathies commonly are associated with poor prognosis, and the underlying etiology of this disorder differs considerably from cardiomyopathies in older children, adolescents, and adults with similar phenotypes. In this review, the major causes of neonatal cardiomyopathy are described.

Mitochondrial encephalomyopathy (Kearns-Sayre syndrome) with complete atrioventricular block: a case report

A pacemaker was implanted into a 17-year-old man with cardiac failure due to complete atrioventricular block complicated by mitochondrial encephalomyopathy (Kearns-Sayre syndrome). Due to the possible complication of latent myocardial dysfunction, it was decided to implant the dual chamber pacemaker (DDD) and the operation mode was set to DDD 70 ppm 1 year after implantation; this alleviated the cardiac failure. In this case, the necessity of preventive pacemaker implantation in the early stage of cardiac failure was recognized.

[Genetic bases of arrhythmias]

We have long known that there are diseases which are inherited from the parents, but it has not been until this last decade, with the introduction of the techniques of molecular biology, that we have been able to study them. These techniques have enable us to localize and detect the gene that causes a disease in the members of a family. The identification of a disease-causing gene does not lead only to the diagnosis and possible treatment of a very select patient population (the one with the familial disease), but also to a better understanding of the molecular basis and pathogenesis of the non-familial forms of the disease. Cardiology, despite having received these techniques more slowly, is now completely. Involved in the study of the molecular basis of cardiac diseases. The first gene to be mapped was that of hypertrophic cardiomyopathy in 1989. Since then, advances have been achieved at all levels in familial cardiac diseases. Hypertension, atherosclerosis, congenital heart diseases, and arrhythmias have all benefitted from the new techniques. Spectacular progress has been achieved in understanding familial heart rhythm disturbances, like long QT syndrome, both as congenital and acquired diseases. In the last five years 4 loci and 3 genes have been identified. The first studies of genetic based therapy have shown that in the near future patients with receive medication depending on the affected gene. Other familial arrhythmias are presently under study. Loci have been detected in some, such as bundle branch block and familial atrial fibrillation. At the speed that the techniques are evolving, and with the impressive advances of the Human Genome Project, we can expect to find the rest of the genes causing familial diseases in the next few years. These results are encouraging and clearly indicate the need for genetic diagnosis in all patients with these diseases. The diagnostic and therapeutic implications of all these discoveries could be of paramount importance.

[Cardiac involvement in neuromuscular diseases]

Many neuromuscular disorders involve the heart, occasionally with overt clinical disease. Muscular dystrophies (dystrophinopathies, limb girdle muscular dystrophy, Emery-Dreifuss muscular dystrophy, Steinert's myotonic dystrophy), congenital myopathies, inflammatory myopathies and metabolic diseases (glycogenosis, periodic paralysis, mitochondrial diseases) may produce dilated or hypertrophic cardiomyopathy and heart rhythm or conduction disturbances. Furthermore the heart is commonly involved in some hereditary and degenerative diseases (Friedreich's ataxia and Kugelberg-Welander syndrome) and acquired (Guillain-Barré syndrome) or inherited (Refsum's disease and Charcot-Marie-Tooth syndrome) polyneuropathies. A cardiologist's high clinical suspicion and a simple but systematic skeletal muscle and peripheral nerve investigation, including muscle enzymes quantification, neurophysiological study and muscle biopsy, are necessary for an accurate diagnosis. In selected patients, more sophisticated biochemical and genetic analysis will be necessary. In most cases, endomyocardial biopsy is not essential for the diagnosis.

Correlation between left ventricular hypertrophy and GAA trinucleotide repeat length in Friedreich's ataxia

BACKGROUND

Friedreich's ataxia (FA), the most common inherited ataxia, is associated frequently with cardiac hypertrophy, and death is often cardiac related. Recently, the disease has been associated with a mutation that consists of an unstable expansion of GAA repeats in the first intron of the gene encoding frataxin on chromosome 9.

METHODS AND RESULTS

We studied 44 consecutive patients with FA, determined the size of GAA expansions in the frataxin gene, and examined the relation between the genotype and cardiac phenotype assessed by M-mode and two-dimensional echocardiography. All the patients were homozygous for the mutation. The size of the GAA expansion on the smaller allele varied from 270 to 1200. We found a correlation between the size of GAA expansion and the left ventricular wall thickness (r = .51, P < .001) and the left ventricular mass index (r = .45, P = .002). Left ventricular hypertrophy was observed in 81% of patients with a number of GAA repeats above the median value of 770 compared with only 14% in the other group (P = .002).

CONCLUSIONS

These data demonstrate that in FA, the severity of left ventricular hypertrophy is related to the number of GAA repeats. These results suggest that abnormalities of the gene encoding frataxin, a protein of unknown function highly expressed in the normal heart, may play an important role in the modulation of cardiac hypertrophy.

Clinical approach to genetic cardiomyopathy in children

BACKGROUND

Cardiomyopathy (CM) remains one of the leading cardiac causes of death in children, although in the majority of cases, the cause is unknown. To have an impact on morbidity and mortality, attention must shift to etiology-specific treatments. The diagnostic evaluation of children with CM of genetic origin is complicated by the large number of rare genetic causes, the broad range of clinical presentations, and the array of specialized diagnostic tests and biochemical assays.

METHODS AND RESULTS

We present a multidisciplinary diagnostic approach to pediatric CM of genetic etiology. We specify criteria for abnormal left ventricular systolic performance and structure that suggest CM based on established normal echocardiographic measurements and list other indications to consider an evaluation for CM. We provide a differential diagnosis of genetic conditions associated with CM, classified as inborn errors of metabolism, malformation syndromes, neuromuscular diseases, and familial isolated CM disorders. A diagnostic strategy is offered that is based on the clinical presentation: biochemical abnormalities, encephalopathy, dysmorphic features or multiple malformations, neuromuscular disease, apparently isolated CM, and pathological specimen findings. Adjunctive treatment measures are recommended for severely ill patients in whom a metabolic cause of CM is suspected. A protocol is provided for the evaluation of moribund patients.

CONCLUSIONS

In summary, we hope to assist pediatric cardiologists and other subspecialists in the evaluation of children with CM for a possible genetic cause using a presentation-based approach. This should increase the percentage of children with CM for whom a diagnosis can be established, with important implications for treatment, prognosis, and genetic counseling.

The therapy of respiratory chain encephalomyopathy: a critical review of the past and current perspective

The mitochondrial respiratory chain encephalomyopathies represent an important group of multisystem disorders. No curative treatment is currently available. A number of measures have been reported to have a theoretical potential to improve respiratory function. These treatment strategies have variable scientific support, many reports being anecdotal. We critically review the various therapeutic measures employed and suggest future treatment directions.

Cardiomyopathy in respiratory chain disorders

Disorders of mitochondrial oxidative phosphorylation may disturb cardiac energy metabolism and cause cardiomyopathy. Twenty one cases from the literature and one further patient with cardiomyopathy due to biochemically defined respiratory chain defects were reviewed for clinical course, morphology, and pathophysiological mechanisms of the cardiomyopathy. All cases showed concentric hypertrophy of the myocardium without an outflow tract obstruction. In most patients the cardiomyopathy was diagnosed early in infancy and showed rapid deterioration with death before the age of 2 years. Hypertrophy of the myocardium appears to result from swelling of the cardiomyocytes caused by accumulation of mitochondria and by morphologically abnormal megamitochondria.

A gene defect that causes conduction system disease and dilated cardiomyopathy maps to chromosome 1p1-1q1

Longitudinal evaluation of a seven generation kindred with an inherited conduction system defect and dilated cardiomyopathy demonstrated autosomal dominant transmission of a progressive disorder that both perturbs atrioventricular conduction and depresses cardiac contractility. To elucidate the molecular genetic basis for this disorder, a genome-wide linkage analysis was performed. Polymorphic loci near the centromere of chromosome 1 demonstrated linkage to the disease locus (maximum multipoint lod score = 13.2 in the interval between D1S305 and D1S176). Based on the disease phenotype and map location we speculate that gap junction protein connexin 40 is a candidate for mutations that result in conduction system disease and dilated cardiomyopathy.

Sinus dysrhythmia in Kearns-Sayre syndrome

Kearns-Sayre syndrome is the triad of progressive external ophthalmoplegia, pigmentary retinopathy, and complete AV block. The etiology is unknown, but is thought to be due to a mitochondrial DNA deletion. Reported electrocardiographic abnormalities include first-degree AV block, fascicular blocks, and complete heart block, as well as non-specific S-T segment changes and T wave abnormalities, but has not included sinus node dysfunction. We report a case with episodes of sinus arrest in an asymptomatic patient with Kearns-Sayre syndrome resulting in pauses lasting up to 6 seconds.

Mitochondrial DNA deletions in dilated cardiomyopathy: a clinical study employing endomyocardial sampling

OBJECTIVES

The aim of this study was to assess the occurrence of the two most commonly encountered mitochondrial DNA (mtDNA) deletions in the hearts of patients with idiopathic dilated cardiomyopathy.

BACKGROUND

The mutation frequency of mtDNA is high, and sporadic cases of cardiomyopathies associated with mtDNA deletions have been described. Reports of increases in mtDNA deletions with advancing age also exist.

METHODS

We studied 15 consecutive patients with typical signs of idiopathic dilated cardiomyopathy, without a family history, together with 16 control hearts obtained at autopsy from patients who died of noncardiac causes. The patients underwent both right and left heart catheterization, during which endomyocardial biopsy samples were taken. The mtDNA in these samples and in the control hearts was analyzed by the polymerase chain reaction technique for the occurrence and proportion of 5- and 7.4-kilobase (kb) deletions (Cambridge sequence map positions from nucleotides 8469 to 13447 and 8637 to 16084, respectively).

RESULTS

The 5-kb mtDNA deletion was observed in the hearts of all of the patients with idiopathic dilated cardiomyopathy, accounting for 0.32 +/- 0.05% (mean +/- SEM) of the total mtDNA. The 7.4-kb deletion was found in 7 of the 15 patients with idiopathic dilated cardiomyopathy and comprised 0.28 +/- 0.08% of the total. The 5- and 7.4-kb deletions were detected in 12 and 9 control hearts, respectively, quantitatively similar to the patients with idiopathic dilated cardiomyopathy. A sigmoidal age dependency of the mtDNA deletions was found both in the patients with cardiomyopathy and in the control hearts, but after elimination of the confounding age variable, there was no difference between these groups.

CONCLUSIONS

Because of the similarity of the age-dependent increase in the frequency of mtDNA deletions in cardiomyopathic and control hearts, the deletions have no causal relation with idiopathic dilated cardiomyopathy. The present results confirm the notion of an increase in mtDNA deletions with advancing age and show that endomyocardial tissue sampling is a feasible method for detecting mtDNA defects in affected hearts.

The causes of dilated cardiomyopathy: a clinicopathologic review of 673 consecutive patients

OBJECTIVES

The purpose of this study was to document the various causes of dilated cardiomyopathy in a large group of adult patients with congestive heart failure.

BACKGROUND

Previous reports of the causes of dilated cardiomyopathy have usually been case reports of a single specific etiology or review articles. The frequency of any single specific heart muscle disease is largely unknown.

METHODS

We evaluated 673 patients referred for congestive heart failure due to dilated cardiomyopathy. The evaluation included medical history, physical examination, routine blood chemistry and hematologic measurements, electrocardiography and echocardiography. Thyroid function tests, antinuclear antibody tests and urinary vanillylmandelic acid and metanephrine levels were also obtained. Endomyocardial biopsy with right heart catheterization was performed in every patient. Coronary arteriography was performed in patients who had at least two standard cardiovascular risk factors or a history suggestive of myocardial ischemia. The cases were retrospectively reviewed, and a final cause for dilated cardiomyopathy was listed for each patient.

RESULTS

The most common causes of dilated cardiomyopathy were idiopathic origin (47%), idiopathic myocarditis (12%) and coronary artery disease (11%). The other identifiable causes of dilated cardiomyopathy made up 31% of the total cases.

CONCLUSIONS

Idiopathic dilated cardiomyopathy is a common cause of congestive heart failure. Specific heart muscle diseases occur with much less frequency.

Successful mitral valve replacement for MELAS

Successful mitral valve replacement for severe mitral regurgitation in a patient with mitochondrial encephalomyopathy is reported. Renal failure due to low cardiac output improved dramatically after mitral valve replacement and he was discharged 10 weeks after surgery. The surgical indication and timing for valvular dysfunction in patients with mitochondrial cardiomyopathy are discussed.

Cardiac transplantation in an incomplete Kearns-Sayre syndrome with mitochondrial DNA deletion

A 38-yr-old man with external ophthalmoplegia, cardiac conduction abnormalities, hearing loss, and ragged-red fibres in skeletal muscle biopsy, developed severe signs of cardiac failure within a few months. Echocardiography and angiography demonstrated a dilated cardiomyopathy. Ubiquinone 140 mg day-1 did not stop the worsening of the cardiac status and cardiac transplantation was performed. Molecular analysis showed a heteroplasmic 4.5 kb mitochondrial DNA deletion in endomyocardial tissue. Eighteen months later, cardiac evolution is good and neurological status is stable.

Mitochondrial DNA deletion diagnosed by analysis of an endomyocardial biopsy specimen from a patient with Kearns-Sayre syndrome and complete heart block

Defects of mitochondrial DNA have been found at necropsy in the myocardium of patients with Kearns-Sayre syndrome. A patient with characteristics typical of Kearns-Sayre syndrome and a complete heart block is described. Southern blot analysis showed a deletion of 3.3 kb in the mitochondrial DNA in an endomyocardial biopsy specimen and in skeletal muscle. The deletion led to the disappearance of the genes for four transfer RNAs and four subunits of complex I (NADH:ubiquinone oxidoreductase) in the mitochondrial respiratory chain. The defect could not be demonstrated in whole blood despite amplification of the mitochondrial DNA region of interest by the polymerase chain reaction technique. There can be heteroplasmy--that is, normal and abnormal mitochondrial DNA populations in one cell--in different tissues, and the degree of heteroplasmy may be crucial in the development of organ-specific symptoms. This patient raises the possibility that some tissues can be specifically enriched with mitochondria with DNA defects and emphasises the need for elective sampling of the target tissue and polymerase chain reaction technique to exclude these defects. The role of mitochondrial DNA defects in idiopathic cardiomyopathies could perhaps be studied by analysis of mitochondrial DNA from endomyocardial biopsy specimens.