Cardiac involvement in mitochondrial DNA disease: clinical spectrum, diagnosis, and management

Longxuetongluo Capsule alleviate ischemia/reperfusion induced cardiomyocyte apoptosis through modulating oxidative stress and mitochondrial dysfunction

BACKGROUND

Chinese dragon's blood, the red resin of Dracaena cochinchinensis (Lour.) S. C. Chen., is widely used to treat cardiovascular and cerebrovascular diseases in China. Longxuetongluo Capsule (LTC) is a total phenolic compound extracted from Chinese dragon's blood, currently used in treating ischemic stroke. Myocardial injury can be aggravated after reperfusion of ischemic myocardium, which is called myocardial ischemia-reperfusion injury (MIRI), and the mechanism of MIRI is complex. However, the exact effect and mechanism of LTC on MIRI are still unclear. We explore the effect of LTC on alleviating MIRI based on mitochondrial dysfunction and oxidative stress.

AIM OF THE STUDY

To explore the cardioprotective mechanism of LTC against MIRI.

MATERIALS AND METHODS

A rat MIRI model was constructed through ligation of the left anterior descending coronary artery, and LTC was given continuously for 28 days before surgery. The H9c2 cardiomyocyte injury model was induced by oxygen-glucose deprivation/reperfusion (OGD/R), and LTC was given 24 h before OGD. Myocardial ischemia areas were detected with 2,3,5-triphenyltetrazolium chloride (TTC) staining. Cardiac histopathological changes were detected with hematoxylin-eosin (HE) staining. And biochemical indexes were detected with serum biochemical kit. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL) staining and flow cytometry were used to detect apoptosis. Fluorescent probes were used to observe reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm), Ca2+and other indexes. MitoTracker staining and immunofluorescence were used to observe the morphology of mitochondria and translocation of dynamin-related protein 1 (Drp1). Finally, immunohistochemistry and Western blotting were used to examine the expression of proteins related to apoptosis, mitochondrial fission and fusion and oxidative stress.

RESULTS

LTC could ameliorate cardiac pathological changes, decrease myocardial infarct area and the content or level of relevant serum cardiac enzymes, indicating that LTC could alleviate MIRI. Meanwhile, LTC could inhibit cardiomyocyte apoptosis via regulating apoptosis-related protein expression, and it could restore mitochondrial morphology, maintain ΔΨm, inhibit mitochondrial ROS generation and Ca2+ accumulation, increase the expression of mitochondrial fusion protein 2 (Mfn2), decrease the level of phosphorylation dynamin-related protein 1 (p-Drp1), and regulate ATP synthesis, thereby significantly ameliorating mitochondrial dysfunction. Moreover, LTC significantly reduced the expression of NADPH oxidase 2 (NOX2), NADPH oxidase 4 (NOX4) and neutrophil cytosolic factor 2 (NOXA2/p67phox), and reduced ROS production.

CONCLUSION

The study demonstrated that LTC could inhibit MIRI induced cardiomyocyte apoptosis by inhibiting ROS generation and mitochondrial dysfunction, and these fundings suggested that LTC can be used to alleviate MIRI, which provides a potential therapeutic approach for future treatment of MIRI.

Electrocardiographic abnormalities in patients with cardiomyopathies

Abnormalities in impulse generation and transmission are among the first signs of cardiac remodeling in cardiomyopathies. Accordingly, 12-lead electrocardiogram (ECG) of patients with cardiomyopathies may show multiple abnormalities. Some findings are suggestive of specific disorders, such as the discrepancy between QRS voltages and left ventricular (LV) mass for cardiac amyloidosis or the inverted T waves in the right precordial leads for arrhythmogenic cardiomyopathy. Other findings are less sensitive and/or specific, but may orient toward a specific diagnosis in a patient with a specific phenotype, such as an increased LV wall thickness or a dilated LV. A "cardiomyopathy-oriented" mindset to ECG reading is important to detect the possible signs of an underlying cardiomyopathy and to interpret correctly the meaning of these alterations, which differs in patients with cardiomyopathies or other conditions.

The West of Scotland Cohort of Mitochondrial Individuals with the m.3243A>G Variant: Variations in Phenotypes and Predictors of Disease Severity

BACKGROUND

The m.3243A>G variant is the commonest mitochondrial (mt) DNA pathogenic variant and a frequent cause of mitochondrial disease. Individuals present with a variety of clinical manifestations from diabetes to neurological events resembling strokes. Due to this, patients are commonly cared for by a multidisciplinary team.

OBJECTIVES

This project aimed to identify patients with confirmed mt.3243A>G-related mitochondrial disease attending the Muscle Clinic at Queen Elizabeth University Hospital in Glasgow. We explored potential correlates between clinical phenotypes and mtDNA heteroplasmy levels, HbA1c levels, body mass index, and specific clinical manifestations. We investigated if there were discrepancies between non-neurological speciality labelling in clinical records and individuals' phenotypes.

METHODS

Data were gathered from the West of Scotland electronic records. Phenotypes were ascertained by a clinician with expertise in mitochondrial disorders. Statistical analyses were applied to study relationships between tissue heteroplasmy, HbA1c and clinical phenotypes including body mass index (BMI).

RESULTS

Forty-six individuals were identified from 31 unrelated pedigrees. Maternally inherited diabetes and deafness was the prominent syndromic phenotype (48%). A significant association was found between overall number of symptoms and bowel dysmotility (p < 0.01). HbA1c was investigated as a predictor of severity with potential association seen. Although used widely as a prognosticator, neither corrected blood nor urine mtDNA heteroplasmy levels were associated with increased number of symptoms. In 74.1% of records, syndromic phenotypes were incorrectly used by non-neurological specialities.

CONCLUSIONS

This m.3243 A > G patient cohort present with marked clinical heterogeneity. Urine and blood heteroplasmy levels are not reliable predictors of disease severity. HbA1c may be a novel predictor of disease severity with further research required to investigate this association. We infer that prognosis may be worse in patients with low BMIs and in those with bowel dysmotility. These results underscore a multidisciplinary approach and highlight a problem with inaccurate use of the existing nomenclature.

Primary mitochondrial diseases

Primary mitochondrial diseases (PMDs) are a heterogeneous group of hereditary disorders characterized by an impairment of the mitochondrial respiratory chain. They are the most common group of genetic metabolic disorders, with a prevalence of 1 in 4,300 people. The presence of leukoencephalopathy is recognized as an important feature in many PMDs and can be a manifestation of mutations in both mitochondrial DNA (classic syndromes such as mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes; myoclonic epilepsy with ragged-red fibers [RRFs]; Leigh syndrome; and Kearns-Sayre syndrome) and nuclear DNA (mutations in maintenance genes such as POLG, MPV17, and TYMP; Leigh syndrome; and mitochondrial aminoacyl-tRNA synthetase disorders). In this chapter, PMDs associated with white matter involvement are outlined, including details of clinical presentations, brain MRI features, and elements of differential diagnoses. The current approach to the diagnosis of PMDs and management strategies are also discussed. A PMD diagnosis in a subject with leukoencephalopathy should be considered in the presence of specific brain MRI features (for example, cyst-like lesions, bilateral basal ganglia lesions, and involvement of both cerebral hemispheres and cerebellum), in addition to a complex neurologic or multisystem disorder. Establishing a genetic diagnosis is crucial to ensure appropriate genetic counseling, multidisciplinary team input, and eligibility for clinical trials.

General approach to treatment of genetic leukoencephalopathies in children and adults

Despite the enormous advancements seen in recent years, curative therapies for patients with genetic leukoencephalopathies are available for only a relatively small number of disorders. Therefore, symptomatic treatment and preventive management of the multiple clinical manifestations of patients with genetic leukoencephalopathies are critical in their care. The goals of the symptomatic treatment are to improve patients' quality of life, increase their survival, and reduce the impact on medical resources and related expenses. The coordinated work of a multidisciplinary team, including all specialists involved in the care of these patients, is the gold standard approach to manage and treat their complex and evolving clinical picture. Along with a multidisciplinary team, the relationship and close collaboration with the patient and their caregivers are essential. Their insight into the disease manifestations and management of the different issues should be integrated with the assessments of the multidisciplinary team to prevent clinical complications and preserve the quality of life of patients and their caregivers. Genetic leukoencephalopathies are very heterogeneous in terms of age of onset, clinical features, and disease course. However, many clinical features and problems are shared by most forms. Consequently, common therapeutic strategies apply to the majority of these diseases. This chapter presents the symptomatic approach for shared core clinical features presented by patients with genetic leukoencephalopathies divided by systems and, for each system, the specificities of some genetic leukoencephalopathies.

A Patient with Mitochondrial Disease on Dialysis with Long-term Follow-up of Cardiomyopathy: An Autopsy Case Report

A 59-year-old man developed diabetes at 24 years old and underwent hemodialysis at 42 years old. At 54 years old, cardiac dysfunction with left ventricular hypertrophy was detected, followed by complete atrioventricular block at 57 years old. The patient was diagnosed with mitochondrial disease based on a myocardial biopsy and the presence of a mitochondrial DNA mutation (3243A>G). He died of septic shock at 59 years old, and an autopsy confirmed mitochondrial cardiomyopathy. If progressive cardiac hypertrophy and conduction disturbances are observed in patients with diabetes mellitus on long-term hemodialysis, mitochondrial disease needs to be considered.

Diagnosis and management of patients with left ventricular hypertrophy: Role of multimodality cardiac imaging. A scientific statement of the Heart Failure Association of the European Society of Cardiology

Left ventricular (LV) hypertrophy consists in an increased LV wall thickness. LV hypertrophy can be either secondary, in response to pressure or volume overload, or primary, i.e. not explained solely by abnormal loading conditions. Primary LV hypertrophy may be due to gene mutations or to the deposition or storage of abnormal substances in the extracellular spaces or within the cardiomyocytes (more appropriately defined as pseudohypertrophy). LV hypertrophy is often a precursor to subsequent development of heart failure. Cardiovascular imaging plays a key role in the assessment of LV hypertrophy. Echocardiography, the first-line imaging technique, allows a comprehensive assessment of LV systolic and diastolic function. Cardiovascular magnetic resonance provides added value as it measures accurately LV and right ventricular volumes and mass and characterizes myocardial tissue properties, which may provide important clues to the final diagnosis. Additionally, scintigraphy with bone tracers is included in the diagnostic algorithm of cardiac amyloidosis. Once the diagnosis is established, imaging findings may help predict future disease evolution and inform therapy and follow-up. This consensus document by the Heart Failure Association of the European Society of Cardiology provides an overview of the role of different cardiac imaging techniques for the differential diagnosis and management of patients with LV hypertrophy.

Acute myocardial infarction in a patient with MELAS syndrome: a possible link?

The mitochondrial encephalomyopathy, lactic acidosis, and stroke (MELAS) syndrome is a mitochondrial disorder, commonly caused by m.3243A>G mutation in the MT-TL1 gene. It encodes for the mitochondrial leucine transfer RNA (tRNA Leu [UUR]), implicated in the translation of proteins involved in the assembly and function of mitochondrial complexes in the electron transport chain. The m.3243A>G mutation determines complex I (CI) deficiency, ultimately leading to NADH accumulation, higher rates of glycolysis in order to compensate for the reduced ATP production and increase in lactates, the end-product of glycolysis. Disruption of the oxidative phosphorylation function with an inability to produce sufficient energy results in multi-organ dysfunction, with high energy demanding cells, such as myocytes and neurons, being the most affected ones. Therefore, MELAS syndrome is characterized by a heterogeneous clinical spectrum. Here we report on a case of a 55-year-old man affected by MELA syndrome with no cardiovascular risk factors. He was admitted to our department because of a non ST-segment elevation myocardial infarction (NSTEMI). A coronary angioplasty of the posterior descending artery and of the left anterior descending artery was realized. Transthoracic echocardiography showed inferior and anterior left ventricular wall hypokinesis together with a moderate left ventricle hypertrophy. Cardiac involvement is reported in about a third of the patients and left ventricular hypertrophy (LVH) is the most common phenotype, with possible dilated cardiomyopathy in end-stage disease; brady- arrhythmias and tachy-arrhythmias are also frequently reported as well as Wolff- Parkinson-White (WPW) syndrome. Organ impairment and clinical manifestations depend on the heteroplasmy level of mutant DNA in cells that can differ among individuals, explaining why some patients present a more severe disease. A clear relationship between MELAS syndrome and atherosclerosis has never been established, however recently advocated. In vitro studies in MELAS patients have shown that higher mitochondrial ROS levels and increased expression of oxidative stress-related genes, as a consequence of complex I deficiency and disrupted electron transport, allow circulating LDL to be promptly oxidized into ox-LDL, contributing to endothelial dysfunction and atherosclerosis plaque formation. In light of the recent evidence suggesting a possible link between mitochondrial disorders and atherosclerosis, we speculate that MELAS syndrome may have played a role in the pathogenesis of coronary artery disease in our patient. Further investigations are needed to confirm a pathogenetic link.

Focal segmental glomerulosclerosis with a mutation in the mitochondrially encoded NADH dehydrogenase 5 gene: A case report

NADH dehydrogenase 5 (ND5) is one of 44 subunits composed of Complex I in mitochondrial respiratory chain. Therefore, a mitochondrially encoded ND5 (MT-ND5) gene mutation causes mitochondrial oxidative phosphorylation (OXPHOS) disorder, resulting in the development of mitochondrial diseases. Focal segmental glomerulosclerosis (FSGS) which had podocytes filled with abnormal mitochondria is induced by mitochondrial diseases. An MT-ND5 mutation also causes FSGS. We herein report a Japanese woman who was found to have proteinuria and renal dysfunction in an annual health check-up at 29 years old. Because her proteinuria and renal dysfunction were persistent, she had a kidney biopsy at 33 years of age. The renal histology showed FSGS with podocytes filled with abnormal mitochondria. The podocytes also had foot process effacement and cytoplasmic vacuolization. In addition, the renal pathological findings showed granular swollen epithelial cells (GSECs) in tubular cells, age-inappropriately disarranged and irregularly sized vascular smooth muscle cells (AiDIVs), and red-coloured podocytes (ReCPos) by acidic dye. A genetic analysis using peripheral mononuclear blood cells and urine sediment cells detected the m.13513 G > A variant in the MT-ND5 gene. Therefore, this patient was diagnosed with FSGS due to an MT-ND5 gene mutation. Although this is not the first case report to show that an MT-ND5 gene mutation causes FSGS, this is the first to demonstrate podocyte injuries accompanied with accumulation of abnormal mitochondria in the cytoplasm.

Healthcare resource utilization of patients with mitochondrial disease in an outpatient hospital setting

BACKGROUND AND OBJECTIVES

Mitochondrial diseases present as multi-system disorders requiring a comprehensive multidisciplinary approach. The data on healthcare resource utilization associated with mitochondrial diseases and the clinical drivers of these costs are limited including for the out-patient setting where the majority of the clinical care for mitochondrial disease patients occurs. We performed a cross-sectional retrospective study of out-patient healthcare resource utilization and costs for patients with a confirmed diagnosis of mitochondrial disease.

METHODS

We recruited participants from the Mitochondrial Disease Clinic in Sydney and stratified them into three groups: those with mitochondrial DNA (mtDNA) mutations (Group 1), those with nuclear DNA (nDNA) mutations and the predominant phenotype of chronic progressive external ophthalmoplegia (CPEO) or optic atrophy (Group 2) and those without a confirmed genetic diagnosis but clinical criteria and muscle biopsy findings supportive of a diagnosis of mitochondrial disease (Group 3). Data was collected through retrospective chart review and out-patient costs were calculated using the Medicare Benefits Schedule.

RESULTS

We analyzed the data from 91 participants and found that Group 1 had the greatest average out-patient costs per person per annum ($838.02; SD 809.72). Neurological investigations were the largest driver of outpatient healthcare costs in all groups (average costs per person per annum:-Group 1: $364.11; SD 340.93, Group 2: $247.83; SD 113.86 and Group 3: $239.57; SD 145.69) consistent with the high frequency (94.5%) of neurological symptoms. Gastroenterological and cardiac-related out-patient costs were also major contributors to out-patient healthcare resource utilization in Groups 1 and 3. In Group 2, ophthalmology was the second-most resource intensive specialty ($136.85; SD 173.35). The Group 3 had the greatest average healthcare resource utilization per person over the entire duration of out-patient clinic care ($5815.86; SD 3520.40) most likely due to the lack of a molecular diagnosis and a less customized management approach.

CONCLUSION

The drivers of healthcare resource utilization are dependent on the phenotype-genotype characteristics. Neurological, cardiac, and gastroenterological costs were the top three drivers in the out-patient clinics unless the patient had nDNA mutations with predominant phenotype of CPEO and/or optic atrophy wherein ophthalmological-related costs were the second most resource intensive driver.

Clinical, Genetic, and Histological Characterization of Patients with Rare Neuromuscular and Mitochondrial Diseases Presenting with Different Cardiomyopathy Phenotypes

Cardiomyopathies are mostly determined by genetic mutations affecting either cardiac muscle cell structure or function. Nevertheless, cardiomyopathies may also be part of complex clinical phenotypes in the spectrum of neuromuscular (NMD) or mitochondrial diseases (MD). The aim of this study is to describe the clinical, molecular, and histological characteristics of a consecutive cohort of patients with cardiomyopathy associated with NMDs or MDs referred to a tertiary cardiomyopathy clinic. Consecutive patients with a definitive diagnosis of NMDs and MDs presenting with a cardiomyopathy phenotype were described. Seven patients were identified: two patients with ACAD9 deficiency (Patient 1 carried the c.1240C>T (p.Arg414Cys) homozygous variant in ACAD9; Patient 2 carried the c.1240C>T (p.Arg414Cys) and the c.1646G>A (p.Ar549Gln) variants in ACAD9); two patients with MYH7-related myopathy (Patient 3 carried the c.1325G>A (p.Arg442His) variant in MYH7; Patient 4 carried the c.1357C>T (p.Arg453Cys) variant in MYH7); one patient with desminopathy (Patient 5 carried the c.46C>T (p.Arg16Cys) variant in DES); two patients with mitochondrial myopathy (Patient 6 carried the m.3243A>G variant in MT-TL1; Patient 7 carried the c.253G>A (p.Gly85Arg) and the c.1055C>T (p.Thr352Met) variants in MTO1). All patients underwent a comprehensive cardiovascular and neuromuscular evaluation, including muscle biopsy and genetic testing. This study described the clinical phenotype of rare NMDs and MDs presenting as cardiomyopathies. A multidisciplinary evaluation, combined with genetic testing, plays a main role in the diagnosis of these rare diseases, and provides information about clinical expectations, and guides management.

α1 Adrenoreceptor antagonism mitigates extracellular mitochondrial DNA accumulation in lung fibrosis models and in patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is increasingly associated with nerve-driven processes and endogenous innate immune ligands such as mitochondrial DNA (mtDNA). Interestingly, a connection between these entities has not been explored. Here, we report that noradrenaline (NA) derived from the lung's adrenergic nerve supply drives α-smooth muscle actin (αSMA)-expressing fibroblast accumulation via mechanisms involving α1 adrenoreceptors and mtDNA. Using the bleomycin model, we compared ablation of the lung's adrenergic nerve supply with surgical adrenal resection and found that NA derived from local but not adrenal sources contributes to experimentally induced lung fibrosis and the emergence of an αSMA+ve fibroblast population expressing adrenoreceptor α-1D (ADRA1D). Therapeutic delivery of the α1 adrenoreceptor antagonist terazosin reversed these changes and suppressed extracellular mtDNA accumulation. Cultured normal human lung fibroblasts displayed α1 adrenoreceptors and in response to costimulation with TGFβ1 and NA adopted ACTA2 expression and extracellular mtDNA release. These findings were opposed by terazosin. Evaluation of a previously studied IPF cohort revealed that patients prescribed α1 adrenoreceptor antagonists for nonpulmonary indications demonstrated improved survival and reduced concentrations of plasma mtDNA. Our observations link nerve-derived NA, α1 adrenoreceptors, extracellular mtDNA, and lung fibrogenesis in mouse models, cultured cells, and humans with IPF. Further study of this neuroinnate connection may yield new avenues for investigation in the clinical and basic science realms.

Mitochondrial Cardiomyopathy: Distinctive Cardiac Phenotype Detected with Cardiovascular MRI

Left ventricular hypertrophy (LVH) has a broad differential diagnosis. Pathogenic variants of mitochondrial DNA are a rare cause of LVH, and cardiac MRI is a powerful technique that may aid in differentiating such rare causes. This case report presents three siblings with a pathogenic variant of the mitochondrially encoded tRNA isoleucine (MT-TI) gene. A distinctive cardiac phenotype was detected with cardiac MRI. Extensive LVH and dilatation and decreased ejection fraction were observed with a pattern of increased T2 signal and extensive late gadolinium enhancement, which was remarkably consistent among all three siblings. Keywords: Cardiomyopathies, MR Imaging, Hypertrophic Cardiomyopathy, Mitochondrial, Inherited Cardiomyopathy, Left Ventricular Hypertrophy, Cardiovascular MRI, Late Gadolinium Enhancement Supplemental material is available for this article. © RSNA, 2023.

Cardiogenic shock in a woman with a mitochondrial cardiomyopathy: a case report

Background

Mitochondrial cardiomyopathy (MCM) is an alteration in cardiac structure and function caused by gene mutations or deletions affecting components of the mitochondrial respiratory chain. We report a case of MCM presenting as cardiogenic shock, ultimately requiring left ventricular assist device (LVAD) placement.

Case summary

A 35-year-old woman with chronic weakness and non-ischaemic cardiomyopathy, on home dobutamine, was referred to our institution for heart transplantation evaluation. She was admitted to the hospital for suspected cardiogenic shock after laboratory tests revealed a lactate level of 5.4 mmol/L (ref: 0.5-2.2 mmol/L). Her hospital course was complicated by persistently undulating lactate levels (0.2-8.6 mmol/L) that increased with exertion and did not correlate with mixed venous oxygen saturation measurements obtained from a pulmonary artery catheter. Electrodiagnostic testing demonstrated a proximal appendicular and axial myopathy. A left deltoid muscle biopsy was performed that demonstrated evidence of a mitochondrial disease on light and electron microscopy. Muscle genetic testing revealed two large-scale mitochondrial deoxyribonucleic acid sequence deletions, confirming the diagnosis of MCM. She subsequently underwent LVAD placement, which was complicated by significant right ventricular failure requiring early mechanical support. She was ultimately discharged home with chronic inotropic support.

Discussion

Mitochondrial cardiomyopathy in adults is a diagnostic and therapeutic challenge. Prompt diagnosis should be made in patients with unknown causes of heart failure via skeletal muscle histopathology guided by electrodiagnostic studies, and targeted genetic testing in affected tissue. Outcomes in adult MCM patients who receive an LVAD are unknown and warrant further investigation.

Approach to the Patient With Short Stature: Genetic Testing

The first step in the evaluation of the short child is to decide whether growth parameters in the context of the history are abnormal or a variant of normal. If growth is considered abnormal, system and hormonal tests are likely to be required, followed by more directed testing, such as skeletal survey and/or genetic screening with karyotype or microarray. In a small percentage of short children in whom a diagnosis has not been reached, this will need to be followed by detailed genetic analysis; currently, exome sequencing using targeted panels relevant to the phenotype is the commonly used test. Clinical scenarios are presented that illustrate how such genetic testing can be used to establish a molecular diagnosis, and how that diagnosis contributes to the management of the short child. New genetic causes for short stature are being recognized on a frequent basis, while the clinical spectrum for known genes is being extended. We recommend that an international repository for short stature conditions is established for new findings to aid dissemination of knowledge, but also to help in the definition of the clinical spectrum both for new and established conditions.

Subclinical cardiac involvement present as electrocardiographic abnormalities in various neuromuscular diseases

Background

Cardiac involvement is commonly present in various neuromuscular diseases which may develop life-threatening consequences. The early manifestation is often asymptomatic which however has been insufficiently studied.

Objectives

We aim to characterize electrocardiographic (ECG) changes in neuromuscular diseases without cardiac symptoms.

Methods

Adults having genetically and/or pathologically confirmed type 1 myotonic dystrophy (DM1), Becker muscular dystrophy (BMD), limb girdle muscular dystrophies (LGMDs) and mitochondrial diseases (MtDs) but without history of heart diseases and cardiovascular symptoms were enrolled. The 12-lead ECG characteristics and other test results at diagnosis were retrieved and analyzed.

Results

196 patients with neuromuscular diseases (44 DM1, 25 BMD, 82 LGMDs, 45 MtDs) were consecutively enrolled. ECG abnormalities were identified in 107 (54.6%) patients with a prevalence of 59.1% in DM1, 76.0% in BMD, 40.2% in LGMDs and 64.4% in MtDs. Conduction block was more commonly present in DM1 than the other groups (P < 0.01), which had a longest PR interval and QRS duration of 186.1 ± 38.3 ms and 104.2 [90.0-108.0]ms, respectively. QT prolongation was most frequently seen in DM1 (P < 0.001). Left ventricular hypertrophy features were found in BMD, LGMDs and MtDs (P < 0.05) without intergroup difference, while a significantly higher right ventricular amplitude is observed in BMD than in other groups (P < 0.001).

Conclusions

Subclinical cardiac involvement is commonly present as ECG abnormalities in multiple adult neuromuscular diseases before associated symptoms occur and show diversity in different groups.

Pathogenic BCS1L Mutation Resulting in Hypertrophic Cardiomyopathy: A Unique Presentation of Nuclear Mitochondrial Disease

A 21-year-old man with sensorineural hearing loss and glaucoma presented with severely limited exercise capacity since childhood. He was found to have biventricular concentric hypertrophy with greatest wall thickening at the posterior and lateral walls of the left ventricle apex (1.7 cm) and the free wall of the right ventricle (1.1 cm). There was no inducible left ventricular outflow tract obstruction. Metabolic testing revealed marked lactic aciduria (1,650.1 μmol/mmol creatinine) and plasma lactate (3.9 mmol/L). A sarcomeric hypertrophic cardiomyopathy gene panel was unremarkable, but mitochondrial gene analysis revealed a homozygous c.385G&gt;A (p.Gly129Arg) pathogenic mutation in the BCS1L gene. This gene is responsible for an assembly subunit of cytochrome complex III in the respiratory transport chain and is the rarest respiratory chain defect. This gene has not frequently been implicated in cardiomyopathy. Mitochondrial hypertrophic cardiomyopathy is more rare than hypertrophic cardiomyopathy resulting from sarcomeric mutations and is more likely to be symmetric, less frequently results in left ventricular outflow tract obstruction, and is more likely to progress to dilated cardiomyopathy. Evidence-based screening protocols have not been established; treatment follows guideline-directed medical therapy for congestive heart failure, including evaluation for heart transplantation. This report expands the phenotype of the BCS1L mutation and suggests that affected patients may need screening for underlying cardiomyopathy.

Currently available therapies in mitochondrial disease

Mitochondrial diseases are a heterogeneous group of multisystem disorders caused by impaired mitochondrial function. These disorders occur at any age and involve any tissue, typically affecting organs highly dependent on aerobic metabolism. Diagnosis and management are extremely difficult due to various underlying genetic defects and a wide range of clinical symptoms. Preventive care and active surveillance are strategies to try to reduce morbidity and mortality by timely treatment of organ-specific complications. More specific interventional therapies are in early phases of development and no effective treatment or cure currently exists. A variety of dietary supplements have been utilized based on biological logic. For several reasons, few randomized controlled trials have been completed to assess the efficacy of these supplements. The majority of the literature on supplement efficacy represents case reports, retrospective analyses and open-label studies. We briefly review selected supplements that have some degree of clinical research support. In mitochondrial diseases, potential triggers of metabolic decompensation or medications that are potentially toxic to mitochondrial function should be avoided. We shortly summarize current recommendations on safe medication in mitochondrial diseases. Finally, we focus on the frequent and debilitating symptoms of exercise intolerance and fatigue and their management including physical training strategies.

Mitochondrial Dysfunction in Cardiac Arrhythmias

Electrophysiological and structural disruptions in cardiac arrhythmias are closely related to mitochondrial dysfunction. Mitochondria are an organelle generating ATP, thereby satisfying the energy demand of the incessant electrical activity in the heart. In arrhythmias, the homeostatic supply-demand relationship is impaired, which is often accompanied by progressive mitochondrial dysfunction leading to reduced ATP production and elevated reactive oxidative species generation. Furthermore, ion homeostasis, membrane excitability, and cardiac structure can be disrupted through pathological changes in gap junctions and inflammatory signaling, which results in impaired cardiac electrical homeostasis. Herein, we review the electrical and molecular mechanisms of cardiac arrhythmias, with a particular focus on mitochondrial dysfunction in ionic regulation and gap junction action. We provide an update on inherited and acquired mitochondrial dysfunction to explore the pathophysiology of different types of arrhythmias. In addition, we highlight the role of mitochondria in bradyarrhythmia, including sinus node dysfunction and atrioventricular node dysfunction. Finally, we discuss how confounding factors, such as aging, gut microbiome, cardiac reperfusion injury, and electrical stimulation, modulate mitochondrial function and cause tachyarrhythmia.

Emergencies cards for neuromuscular disorders 1st Consensus Meeting from UILDM - Italian Muscular Dystrophy Association Workshop report

Acute hospitalisation may be required to support patients with Neuromuscular disorders (NMDs) mainly experiencing respiratory complications, swallowing difficulties, heart failure, urgent surgical procedures. As NMDs may need specific treatments, they should be ideally managed in specialized hospitals. Nevertheless, if urgent treatment is required, patients with NMD should be managed at the closest hospital site, which may not be a specialized centre where local emergency physicians have the adequate experience to manage these patients. Although NMDs are a group of conditions that can differ in terms of disease onset, progression, severity and involvement of other systems, many recommendations are transversal and apply to the most frequent NMDs. Emergency Cards (EC), which report the most common recommendations on respiratory and cardiac issues and provide indications for drugs/treatments to be used with caution, are actively used in some countries by patients with NMDs. In Italy, there is no consensus on the use of any EC, and a minority of patients adopt it regularly in case of emergency. In April 2022, 50 participants from different centres in Italy met in Milan, Italy, to agree on a minimum set of recommendations for urgent care management which can be extended to the vast majority of NMDs. The aim of the workshop was to agree on the most relevant information and recommendations regarding the main topics related to emergency care of patients with NMD in order to produce specific ECs for the 13 most frequent NMDs.

Mechanisms behind diffuse idiopathic peripheral neuropathy in humans - a systematic review

Introduction: Diffuse peripheral neuropathy is a well-known complication of several conditions, whereas many patients have peripheral neuropathy of unknown etiology and pathophyisology. Increased knowledge of mechanisms may provide insight into enteric neuropathy with gastrointestinal dysmotility. The aim of the present systematic review was to identify mechanisms behind diffuse idiopathic peripheral neuropathies in humans.Methods: Searches were performed in PubMed, Embase, and Web of Science. Human original and review articles, written in English, describing mechanisms behind diffuse peripheral neuropathy verified by objective examinations were intended to be studied. Articles that described animal models, well-described hereditary diseases, drug-induced neuropathy, pain syndromes, malnutrition, and local neuropathy were excluded.Results: In total, 4712 articles were identified. After scrutinizing titles and abstracts, 633 remained and were studied in full text. After the removal of articles not fulfilling inclusion or exclusion criteria, 52 were finally included in this review. The most frequently described neuropathy was diabetic neuropathy, with a wide range of mechanisms involving mitochondrial dysfunction such as oxidative stress and inflammation. Microvascular changes in diabetes and vasculitis lead to ischemia and secondary oxidative stress with inflammation. Structural changes in neurons and glial cells are observed, with abnormalities in different neurotrophic factors. Neuropathy induced by autoantibodies or immunological mechanisms is described in infectious and systemic inflammatory diseases. Several ion channels may be involved in painful neuropathy. No study identified why some patients mainly develop large fiber neuropathy and others small fiber neuropathy.Conclusion: Metabolic and immunological factors and channelopathy may be considered in diffuse idiopathic peripheral neuropathy.

Role of cardiovascular magnetic resonance in the clinical evaluation of left ventricular hypertrophy: a 360° panorama

Left ventricular hypertrophy (LVH) is a frequent imaging finding in the general population. In order to identify the precise etiology, a comprehensive diagnostic approach should be adopted, including the prevalence of each entity that may cause LVH, family history, clinical, electrocardiographic and imaging findings. By providing a detailed evaluation of the myocardium, cardiovascular magnetic resonance (CMR) has assumed a central role in the differential diagnosis of left ventricular hypertrophy, with the technique of parametric imaging allowing more refined tissue characterization. This article aims to establish a parallel between pathophysiological features and imaging findings through the broad spectrum of LVH entities, emphasizing the role of CMR in the differential diagnosis.

Mitochondrial Cardiomyopathy: Molecular Epidemiology, Diagnosis, Models, and Therapeutic Management

Mitochondrial cardiomyopathy (MCM) is characterized by abnormal heart-muscle structure and function, caused by mutations in the nuclear genome or mitochondrial DNA. The heterogeneity of gene mutations and various clinical presentations in patients with cardiomyopathy make its diagnosis, molecular mechanism, and therapeutics great challenges. This review describes the molecular epidemiology of MCM and its clinical features, reviews the promising diagnostic tests applied for mitochondrial diseases and cardiomyopathies, and details the animal and cellular models used for modeling cardiomyopathy and to investigate disease pathogenesis in a controlled in vitro environment. It also discusses the emerging therapeutics tested in pre-clinical and clinical studies of cardiac regeneration.

Mitochondrial mutations in protein coding genes of respiratory chain including complexes IV, V, and mt-tRNA genes are associated risk factors for congenital heart disease

Most studies aiming at unraveling the molecular events associated with cardiac congenital heart disease (CHD) have focused on the effect of mutations occurring in the nuclear genome. In recent years, a significant role has been attributed to mitochondria for correct heart development and maturation of cardiomyocytes. Moreover, numerous heart defects have been associated with nucleotide variations occurring in the mitochondrial genome, affecting mitochondrial functions and cardiac energy metabolism, including genes encoding for subunits of respiratory chain complexes. Therefore, mutations in the mitochondrial genome may be a major cause of heart disease, including CHD, and their identification and characterization can shed light on pathological mechanisms occurring during heart development. Here, we have analyzed mitochondrial genetic variants in previously reported mutational genome hotspots and the flanking regions of mt-ND1, mt-ND2, mt-COXI, mt-COXII, mt-ATPase8, mt-ATPase6, mt-COXIII, and mt-tRNAs (Ile, Gln, Met, Trp, Ala, Asn, Cys, Tyr, Ser, Asp, and Lys) encoding genes by polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) in 200 patients with CHD, undergoing cardiac surgery. A total of 23 mitochondrial variations (5 missense mutations, 8 synonymous variations, and 10 nucleotide changes in tRNA encoding genes) were identified and included 16 novel variants. Additionally, we showed that intracellular ATP was significantly reduced (P=0.002) in CHD patients compared with healthy controls, suggesting that the mutations have an impact on mitochondrial energy production. Functional and structural alterations caused by the mitochondrial nucleotide variations in the gene products were studied in-silico and predicted to convey a predisposing risk factor for CHD. Further studies are necessary to better understand the mechanisms by which the alterations identified in the present study contribute to the development of CHD in patients.

Beyond Sarcomeric Hypertrophic Cardiomyopathy: How to Diagnose and Manage Phenocopies

PURPOSE OF REVIEW

We describe the most common phenocopies of hypertrophic cardiomyopathy, their pathogenesis, and clinical presentation highlighting similarities and differences. We also suggest a step-by-step diagnostic work-up that can guide in differential diagnosis and management.

RECENT FINDINGS

In the last years, a wider application of genetic testing and the advances in cardiac imaging have significantly changed the diagnostic approach to HCM phenocopies. Different prognosis and management, with an increasing availability of disease-specific therapies, make differential diagnosis mandatory. The HCM phenotype can be the cardiac manifestation of different inherited and acquired disorders presenting different etiology, prognosis, and treatment. Differential diagnosis requires a cardiomyopathic mindset allowing to recognize red flags throughout the diagnostic work-up starting from clinical and family history and ending with advanced imaging and genetic testing. Different prognosis and management, with an increasing availability of disease-specific therapies make differential diagnosis mandatory.

Inefficient Batteries in Heart Failure: Metabolic Bottlenecks Disrupting the Mitochondrial Ecosystem

Mitochondrial abnormalities have long been described in the setting of cardiomyopathies and heart failure (HF), yet the mechanisms of mitochondrial dysfunction in cardiac pathophysiology remain poorly understood. Many studies have described HF as an energy-deprived state characterized by a decline in adenosine triphosphate production, largely driven by impaired oxidative phosphorylation. However, impairments in oxidative phosphorylation extend beyond a simple decline in adenosine triphosphate production and, in fact, reflect pervasive metabolic aberrations that cannot be fully appreciated from the isolated, often siloed, interrogation of individual aspects of mitochondrial function. With the application of broader and deeper examinations into mitochondrial and metabolic systems, recent data suggest that HF with preserved ejection fraction is likely metabolically disparate from HF with reduced ejection fraction. In our review, we introduce the concept of the mitochondrial ecosystem, comprising intricate systems of metabolic pathways and dynamic changes in mitochondrial networks and subcellular locations. The mitochondrial ecosystem exists in a delicate balance, and perturbations in one component often have a ripple effect, influencing both upstream and downstream cellular pathways with effects enhanced by mitochondrial genetic variation. Expanding and deepening our vantage of the mitochondrial ecosystem in HF is critical to identifying consistent metabolic perturbations to develop therapeutics aimed at preventing and improving outcomes in HF.

Mitochondrial Dysfunction and Cardiovascular Disease: Pathophysiology and Emerging Therapies

Mitochondria ensure the supply of cellular energy through the production of ATP via oxidative phosphorylation. The alteration of this process, called mitochondrial dysfunction, leads to a reduction in ATP and an increase in the production of reactive oxygen species (ROS). Mitochondrial dysfunction can be caused by mitochondrial/nuclear DNA mutations, or it can be secondary to pathological conditions such as cardiovascular disease, aging, and environmental stress. The use of therapies aimed at the prevention/correction of mitochondrial dysfunction, in the context of the specific treatment of cardiovascular diseases, is a topic of growing interest. In this context, the data are conflicting since preclinical studies are numerous, but there are no large randomized studies.

Low Prevalence of Cardiomyopathy in Patients with Mitochondrial Disease and Neurological Manifestations

Patients with mitochondrial diseases can develop cardiomyopathy but with variable expressivity and penetrance. Our prospective study enrolled and evaluated a cohort of 53 patients diagnosed with chronic progressive ophthalmoplegia (CPEO, n = 34), Kearns-Sayre syndrome (KSS, n = 3), neuropathy ataxia and retinitis pigmentosa (NARP, n = 1), myoclonic epilepsy with ragged red fibers (MERRF, n = 1), Harel-Yoon Syndrome (HYS, n = 1) and 13 patients with undefined mitochondrial diseases, presenting primarily with neurological symptoms. Over a 4-year period, six patients in our study cohort were diagnosed with heart disease (11.3%), with only three patients having defined cardiomyopathy (5.7%). Cardiomyopathy was present in a 21-year-old patient with HYS and two CPEO patients having mild cardiomyopathy at an older age. Two CPEO patients had congenital heart disease, and a third CPEO had LV hypertrophy secondary to hypertension. In three patients, traditional risk factors for heart disease, including dyslipidemia, hypertension, and respiratory disease, were present. The majority of our adult cohort of patients have normal cardiac investigations with a median left ventricular (LV) ejection fraction of 59.0%, indexed LV mass of 67.0 g/m², and normal diastolic and valvular function at baseline. A 12-lead electrocardiogram showed normal cardiac conduction across the study cohort. Importantly, follow-up assessments showed consistent cardiac structure and function. Our study shows a low prevalence of cardiomyopathy and highlights the breadth of phenotypic variability in patients with mitochondrial disorders. The presence of cardiovascular risk factors and aging are important comorbidities in our cohort.

Screening and prevalence of cardiac abnormalities on electro- and echocardiography in a large cohort of patients with mitochondrial disease

BACKGROUND

In patients with primary mitochondrial disease (MD), screening with electrocardiogram (ECG) and transthoracic echocardiography (TTE) is warranted according to current guidelines as structural cardiac abnormalities are frequent. This study aims to evaluate the cardiac phenotype of a large Dutch cohort of patients with MD and investigates whether ECG alone is sufficient for predicting structural cardiac abnormalities on TTE.

METHODS

In this retrospective cohort study, genetically confirmed MD patients >18 years old with an available ECG and TTE were included. Newcastle Mitochondrial Disease Scale for Adults (NMDAS) scores were assessed. ECG's were evaluated for rhythm and conduction disorders, voltage criteria for left ventricular hypertrophy (LVH) and repolarization disorders. Echocardiographic evaluation included left and right ventricular volumes and function, and presence of LVH or concentric remodeling.

RESULTS

In total, 200 MD patients were included with a median age of 45 years (IQR; 37-57) of whom 36% were male. Of all MD patients, 35% had abnormalities on ECG and 61% on TTE. Most frequent structural cardiac abnormalities on TTE were: global longitudinal strain > - 18% (54%), concentric remodeling (27%) and left ventricular (LV) ejection fraction <52% (14%). Patients with maternally inherited diabetes and deafness (MIDD) and mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) had the highest prevalence of ECG abnormalities (50% and 47%). TTE abnormalities were most prevalent in patients with MIDD (75%), followed by mitochondrial myopathy (MM) (55%), MELAS (47%) and Mitochondrial Epilepsy and Ragged Red Fibers (MERRF) (47%). MD patients with a high disease severity (NMDAS ≥21) had a higher prevalence of ECG abnormalities (44%, p = 0.039) and structural cardiac abnormalities (72%, p = 0.004) compared to patients with a NMDAS score of 11-20 and ≤ 10 (ECG: 34% and 19%; TTE: 63% and 39%). ECG abnormalities had a positive predictive value of 74% and a negative predictive value of 53% for structural cardiac abnormalities on TTE.

CONCLUSION

MD patients frequently have cardiac involvement especially patients with MIDD, MELAS or high NMDAS score. ECG as sole screening parameter is insufficient to detect structural cardiac abnormalities.

A Comprehensive Outlook on Dilated Cardiomyopathy (DCM): State-Of-The-Art Developments with Special Emphasis on OMICS-Based Approaches

Dilated cardiomyopathy (DCM) remains an enigmatic cardiovascular disease (CVD) condition characterized by contractile dysfunction of the myocardium due to dilation of the ventricles. DCM is one of the major forms of CVD contributing to heart failure. Dilation of the left or both ventricles with systolic dysfunction, not explained by known causes, is a hallmark of DCM. Progression of DCM leads to heart failure. Genetic and various other factors greatly contribute to the development of DCM, but the etiology has still remained elusive in a large number of cases. A significant number of studies have been carried out to identify the genetic causes of DCM. These candidate-gene studies revealed that mutations in the genes of the fibrous, cytoskeletal, and sarcomeric proteins of cardiomyocytes result in the development of DCM. However, a significant proportion of DCM patients are idiopathic in nature. In this review, we holistically described the symptoms, causes (in adults and newborns), genetic basis, and mechanistic progression of DCM. Further, we also summarized the state-of-the-art diagnosis, available biomarkers, treatments, and ongoing clinical trials of potential drug regimens. DCM-mediated heart failure is on the rise worldwide including in India. The discovery of biomarkers with a better prognostic value is the need of the hour for better management of DCM-mediated heart failure patients. With the advent of next-generation omics-based technologies, it is now possible to probe systems-level alterations in DCM patients pertaining to the identification of novel proteomic and lipidomic biomarkers. Here, we also highlight the onset of a systems-level study in Indian DCM patients by applying state-of-the-art mass-spectrometry-based “clinical proteomics” and “clinical lipidomics”.

Endocrine Manifestations and New Developments in Mitochondrial Disease

Mitochondrial diseases are a group of common inherited diseases causing disruption of oxidative phosphorylation. Some patients with mitochondrial disease have endocrine manifestations, with diabetes mellitus being predominant but also include hypogonadism, hypoadrenalism, and hypoparathyroidism. There have been major developments in mitochondrial disease over the past decade that have major implications for all patients. The collection of large cohorts of patients has better defined the phenotype of mitochondrial diseases and the majority of patients with endocrine abnormalities have involvement of several other systems. This means that patients with mitochondrial disease and endocrine manifestations need specialist follow-up because some of the other manifestations, such as stroke-like episodes and cardiomyopathy, are potentially life threatening. Also, the development and follow-up of large cohorts of patients means that there are clinical guidelines for the management of patients with mitochondrial disease. There is also considerable research activity to identify novel therapies for the treatment of mitochondrial disease. The revolution in genetics, with the introduction of next-generation sequencing, has made genetic testing more available and establishing a precise genetic diagnosis is important because it will affect the risk for involvement for different organ systems. Establishing a genetic diagnosis is also crucial because important reproductive options have been developed that will prevent the transmission of mitochondrial disease because of mitochondrial DNA variants to the next generation.

Arrhythmia prevalence and sudden death risk in adults with the m.3243A>G mitochondrial disorder

AIMS

To define the prevalence of non-sustained tachyarrhythmias and bradyarrhythmias in patients with the m.3243A>G mitochondrial genotype and a previously defined, profile, associated with 'high sudden-death risk'.

METHODS AND RESULTS

Patients at high risk of sudden death because of combinations of ventricular hypertrophy, mitochondrial encephalopathy, lactic acidosis and stroke-like episodes family phenotype, epilepsy or high mutation load, due to the m.3243A>G mutation, were identified from a mitochondrial cohort of 209 patients. All recruited had serial ECG and echo assessments previously according to schedule, had an ECG-loop recorder implanted and were followed for as long as the device allowed. Devices were programmed to detect non-sustained brady- or tachy-arrhythmias. This provided comprehensive rhythm surveillance and automatic downloads of all detections to a monitoring station for cardiology interpretation. Those with sinus tachycardia were treated with beta-blockers and those with ventricular hypertrophy received a beta-blocker and ACE-inhibitor combination.Nine consecutive patients, approached (37.2±3.9 years, seven males) and consented, were recruited. None died and no arrhythmias longer than 30s duration occurred during 3-year follow-up. Three patients reported palpitations but ECGs correlated with sinus rhythm. One manifest physiological, sinus pauses >3.5 s during sleep and another had one asymptomatic episode of non-sustained ventricular tachycardia.

CONCLUSIONS

Despite 'high-risk' features for sudden death, those studied had negligible prevalence of arrhythmias over prolonged follow-up. By implication, the myocardium in this genotype is not primarily arrhythmogenic. Arrhythmias may not explain sudden death in patients without Wolff-Parkinson-White or abnormal atrioventricular conduction or, it must require a confluence of other, dynamic, proarrhythmic factors to trigger them.

Heteroplasmic mitochondrial DNA variants in cardiovascular diseases

Mitochondria are implicated in the pathogenesis of cardiovascular diseases (CVDs) but the reasons for this are not well understood. Maternally-inherited population variants of mitochondrial DNA (mtDNA) which affect all mtDNA molecules (homoplasmic) are associated with cardiometabolic traits and the risk of developing cardiovascular disease. However, it is not known whether mtDNA mutations only affecting a proportion of mtDNA molecules (heteroplasmic) also play a role. To address this question, we performed a high-depth (~1000-fold) mtDNA sequencing of blood DNA in 1,399 individuals with hypertension (HTN), 1,946 with ischemic heart disease (IHD), 2,146 with ischemic stroke (IS), and 723 healthy controls. We show that the per individual burden of heteroplasmic single nucleotide variants (mtSNVs) increases with age. The age-effect was stronger for low-level heteroplasmies (heteroplasmic fraction, HF, 5-10%), likely reflecting acquired somatic events based on trinucleotide mutational signatures. After correcting for age and other confounders, intermediate heteroplasmies (HF 10-95%) were more common in hypertension, particularly involving non-synonymous variants altering the amino acid sequence of essential respiratory chain proteins. These findings raise the possibility that heteroplasmic mtSNVs play a role in the pathophysiology of hypertension.

Diagnosis and Management of Rare Cardiomyopathies in Adult and Paediatric Patients. A Position Paper of the Italian Society of Cardiology (SIC) and Italian Society of Paediatric Cardiology (SICP)

Cardiomyopathies (CMPs) are myocardial diseases in which the heart muscle is structurally and functionally abnormal in the absence of coronary artery disease, hypertension, valvular disease and congenital heart disease sufficient to cause the observed myocardial abnormality. Thought for a long time to be rare diseases, it is now clear that most of the CMPs can be easily observed in clinical practice. However, there is a group of specific heart muscle diseases that are rare in nature whose clinical/echocardiographic phenotypes resemble those of the four classical morphological subgroups of hypertrophic, dilated, restrictive, arrhythmogenic CMPs. These rare CMPs, often but not solely diagnosed in infants and paediatric patients, should be more properly labelled as specific CMPs. Emerging consensus exists that these conditions require tailored investigation and management. Indeed, an appropriate understanding of these conditions is mandatory for early treatment and counselling. At present, however, the multisystemic and heterogeneous presentation of these entities is a challenge for clinicians, and time delay in diagnosis is a significant concern. The aim of this paper is to define practical recommendations for diagnosis and management of the rare CMPs in paediatric or adult age. A modified Delphi method was adopted to grade the recommendations proposed by each member of the writing committee.

Complement C1q Binding Protein (C1QBP): Physiological Functions, Mutation-Associated Mitochondrial Cardiomyopathy and Current Disease Models

Complement C1q binding protein (C1QBP, p32) is primarily localized in mitochondrial matrix and associated with mitochondrial oxidative phosphorylative function. C1QBP deficiency presents as a mitochondrial disorder involving multiple organ systems. Recently, disease associated C1QBP mutations have been identified in patients with a combined oxidative phosphorylation deficiency taking an autosomal recessive inherited pattern. The clinical spectrum ranges from intrauterine growth restriction to childhood (cardio) myopathy and late-onset progressive external ophthalmoplegia. This review summarizes the physiological functions of C1QBP, its mutation-associated mitochondrial cardiomyopathy shown in the reported available patients and current experimental disease platforms modeling these conditions.

Phenotype and pathology of the dilated cardiomyopathy with ataxia syndrome in children

The dilated cardiomyopathy with ataxia syndrome (DCMA) is an autosomal recessive mitochondrial disease caused by mutations in the DnaJ heat shock protein family (Hsp40) member C19 (DNAJC19) gene. DCMA or 3-methylglutaconic aciduria type V is globally rare, but the largest number of patients in the world is found in the Hutterite population of southern Alberta in Canada. We provide an update on phenotypic findings, natural history, pathological findings, and our clinical experience. We analyzed all available records for 43 patients diagnosed with DCMA between 2005 and 2015 at the Alberta Children's Hospital. All patients studied were Hutterite and homozygous for the causative DNAJC19 variant (c.130-1G>C, IVS3-1G>C) and had elevated levels of 3-methyglutaconic acid. We calculated a birth prevalence of 1.54 cases per 1000 total births in the Hutterite community. Children were small for gestational age at birth and frequently required supplemental nutrition (63%) or surgical placement of a gastrostomy tube (35%). Early mortality in this cohort was high (40%) at a median age of 13 months (range 4-294 months). Congenital anomalies were common as was dilated cardiomyopathy (50%), QT interval prolongation (83%), and developmental delay (95%). Tissue pathology was analyzed in a limited number of patients and demonstrated subendocardial fibrosis in the heart, macrovesicular steatosis and fibrosis in the liver, and structural abnormalities in mitochondria. This report provides clinical details for a cohort of children with DCMA and the first presentation of tissue pathology for this disorder. Despite sharing common genetic etiology and environment, the disease is highly heterogeneous for reasons that are not understood. DCMA is a clinically heterogeneous systemic mitochondrial disease with significant morbidity and mortality that is common in the Hutterite population of southern Alberta.

Chronic GPER activation prevents ischemia/reperfusion injury in ovariectomized rats

During menopause women are exposed to an increase in cardiovascular risk. G protein-coupled estrogen receptor (GPER) is known to mediate several of the protective effects of such hormones. G1 was described as a selective and synthetic agonist for GPER. The aim of the present research is to evaluate the effect of a chronic treatment with G1 in ovariectomized (OVX) rats exposed to ischemia/reperfusion (I/R). Considering the hypothesis that an impaired mitochondrial state could be involved in the alterations produced in OVX rats, other objective of this study was to investigate it in an isolated preparation. Three months old rats were assigned to undergo either bilateral ovariectomy or sham operation. The OVX rats were randomly treated during one month with either G1 or vehicle. Cardiac mitochondria from OVX rats showed a depolarized membrane potential and a decreased calcium retention capacity in comparison with Sham rats, which were prevented by chronic G1 treatment. I/R caused a higher decrease of left ventricular developed pressure and a higher increase of left ventricular end diastolic pressure in OVX compared to Sham hearts. These altered mechanical parameters were prevented by G1. The induced infarct size was significantly higher in OVX, which was reduced by G1 treatment. These results indicate that the mitochondrial state in OVX rats is impaired, accompanied by an altered mechanical response after ischemia and reperfusion injury, which was effectively prevented with chronic treatment with G1. The present study may provide further insights for the potential development of a therapy based on the GPER modulation.

Development of Leigh syndrome with a high probability of cardiac manifestations in infantile-onset patients with m.14453G > A

The m.14453G > A mutation in MT-ND6 has been described in a few patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes or Leigh syndrome.However, the clinical spectrum and molecular characteristics are unclear.Here, we present four infantile-onset patients with m.14453G > A-associated Leigh syndrome. All four patients had brainstem lesions with basal ganglia lesions, and two patients had cardiac manifestations. Decreased ND6 protein expression and immunoreactivity were observed in patient-derived samples. There was no clear correlation between heteroplasmy levels and onset age or between heteroplasmy levels and phenotype; however, infantile onset was associated with Leigh syndrome.

Cardiovascular Involvement in mtDNA Disease: Diagnosis, Management, and Therapeutic Options

Mitochondrial diseases (MD) include an heterogenous group of systemic disorders caused by sporadic or inherited mutations in nuclear or mitochondrial DNA (mtDNA), causing impairment of oxidative phosphorylation system. Hypertrophic cardiomyopathy is the dominant pattern of cardiomyopathy in all forms of mtDNA disease, being observed in almost 40% of the patients. Dilated cardiomyopathy, left ventricular noncompaction, and conduction system disturbances have been also reported. In this article, the authors discuss the current clinical knowledge on MD, focusing on diagnosis and management of mitochondrial diseases caused by mtDNA mutations.

Mitochondrial Disorders

BACKGROUND

Mitochondrial disorders are among the most common heritable diseases, with an overall lifetime risk of approximately one in 1500. Nonetheless, their diagnosis is often missed because of their extreme phenotypic and genotypic heterogeneity.

METHODS

This review is based on publications retrieved by a selective literature search on the clinical features, genetics, pathogenesis, diagnosis, and treatment of mitochondrial diseases.

RESULTS

Pathogenic defects of energy metabolism have been described to date in over 400 genes. Only a small number of these genes lie in the mitochondrial DNA; the corresponding diseases are either maternally inherited or of sporadic distribution. The remaining diseaseassociated genes are coded in nuclear DNA and cause diseases that are inherited according to Mendelian rules, mostly autosomal recessive. The most severely involved organs are generally those with the highest energy requirements, including the brain, the sensory epithelia, and the extraocular, cardiac, and skeletal musculature. Typical manifestations include epileptic seizures, stroke-like episodes, hearing loss, retinopathy, external ophthalmoparesis, exercise intolerance, and diabetes mellitus. More than two manifestations of these types should arouse suspicion of a disease of energy metabolism. The severity of mitochondrial disorders ranges from very severe disease, already evident in childhood, to relatively mild disease arising in late adulthood. The diagnosis is usually confirmed with molecular-genetic methods. Symptomatic treatment can improve patients' quality of life. The only disease-modifying treatment that has been approved to date is idebenone for the treatment of Leber hereditary optic neuropathy. Intravitreal gene therapy has also been developed for the treatment of this disease; its approval by the European Medicines Agency is pending.

CONCLUSION

Patients with mitochondrial diseases have highly varied manifestations and can thus present to physicians in practically any branch of medicine. A correct diagnosis is the prerequisite for genetic counseling and for the initiation of personalized treatment.

Disease Modeling of Mitochondrial Cardiomyopathy Using Patient-Specific Induced Pluripotent Stem Cells

Mitochondrial cardiomyopathy (MCM) is characterized as an oxidative phosphorylation disorder of the heart. More than 100 genetic variants in nuclear or mitochondrial DNA have been associated with MCM. However, the underlying molecular mechanisms linking genetic variants to MCM are not fully understood due to the lack of appropriate cellular and animal models. Patient-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iPSC-CMs) provide an attractive experimental platform for modeling cardiovascular diseases and predicting drug efficacy to such diseases. Here we introduce the pathological and therapeutic studies of MCM using iPSC-CMs and discuss the questions and latest strategies for research using iPSC-CMs.

Ventricular arrhythmias in athletes: Role of a comprehensive diagnostic workup

BACKGROUND

Ventricular arrhythmias (VAs) represent a critical issue with regard to sports eligibility assessment in athletes. The ideal diagnostic evaluation of competitive and leisure-time athletes with complex VAs has not been clearly defined.

OBJECTIVE

The purpose of this study was to assess the clinical implications of invasive electrophysiological assessments and endomyocardial biopsy (EMB) among athletes with VAs.

METHODS

We evaluated 227 consecutive athletes who presented to our institutions after being disqualified from participating in sports because of VAs. After noninvasive tests, electrophysiological study (EPS), electroanatomic mapping (EAM), and EAM- or cardiac magnetic resonance imaging-guided EMB was performed, following a prespecified protocol. Sports eligibility status was redefined at 6-month follow-up.

RESULTS

From our sample, 188 athletes (82.8%) underwent EAM and EPS, and 42 (15.2%) underwent EMB. A diagnosis of heart disease could be formulated in 30% of the study population (67/227; 95% confidence interval [CI] 0.24-0.36) after noninvasive tests; in 37% (83/227; 95% CI 31%-43%) after EPS and EAM; and in 45% (102/227; 95% CI 39%-51%) after EMB. In the subset of athletes undergoing EMB, invasive diagnostic workup allowed diagnostic reclassification of half of the athletes (n = 21 [50%]). Reclassification was particularly common among subjects without definitive findings after noninvasive evaluation (n = 23; 87% reclassified). History of syncope, abnormal echocardiogram, presence of late gadolinium enhancement, and abnormal EAM were linked to sports ineligibility at 6-month follow-up.

CONCLUSION

A comprehensive invasive workup provided additional diagnostic elements and could improve the sports eligibility assessment of athletes presenting with VAs. The extensive invasive evaluation presented could be especially helpful when noninvasive tests show unclear findings.

Cardiovascular Outcomes in Patients With Mitochondrial Disease in the United States: A Propensity Score Analysis

Mitochondrial disease comprises a wide range of genetic disorders caused by mitochondrial dysfunction. Its rarity, however, has limited the ability to assess its effects on clinical outcomes. To evaluate this relationship, we collected data from the 2016 National Inpatient Sample, which includes data from >7 million hospital stays. We identified 705 patients (mean age, 22 ± 20.7 yr; 54.2% female; 67.4% white) whose records included the ICD-10-CM code E88.4. We also identified a propensity-matched cohort of 705 patients without mitochondrial disease to examine the effect of mitochondrial disease on major adverse cardiovascular events, including all-cause in-hospital death, cardiac arrest, and acute congestive heart failure. Patients with mitochondrial disease were at significantly greater risk of major adverse cardiovascular events (odds ratio [OR]=2.42; 95% CI, 1.29-4.57; P=0.005), systolic heart failure (OR=2.37; 95% CI, 1.08-5.22; P=0.027), and all-cause in-hospital death (OR=14.22; 95% CI, 1.87-108.45; P<0.001). These findings suggest that mitochondrial disease significantly increases the risk of inpatient major adverse cardiovascular events.

Loss of the mitochondrial phosphate carrier SLC25A3 induces remodeling of the cardiac mitochondrial protein acylome

Mitochondria are recognized as signaling organelles because, under stress, mitochondria can trigger various signaling pathways to coordinate the cell's response. The specific pathway(s) engaged by mitochondria in response to mitochondrial energy defects in vivo and in high-energy tissues like the heart are not fully understood. Here, we investigated cardiac pathways activated in response to mitochondrial energy dysfunction by studying mice with cardiomyocyte-specific loss of the mitochondrial phosphate carrier (SLC25A3), an established model that develops cardiomyopathy as a result of defective mitochondrial ATP synthesis. Mitochondrial energy dysfunction induced a striking pattern of acylome remodeling, with significantly increased post-translational acetylation and malonylation. Mass spectrometry-based proteomics further revealed that energy dysfunction-induced remodeling of the acetylome and malonylome preferentially impacts mitochondrial proteins. Acetylation and malonylation modified a highly interconnected interactome of mitochondrial proteins, and both modifications were present on the enzyme isocitrate dehydrogenase 2 (IDH2). Intriguingly, IDH2 activity was enhanced in SLC25A3-deleted mitochondria, and further study of IDH2 sites targeted by both acetylation and malonylation revealed that these modifications can have site-specific and distinct functional effects. Finally, we uncovered a novel crosstalk between the two modifications, whereby mitochondrial energy dysfunction-induced acetylation of sirtuin 5 (SIRT5), inhibited its function. Because SIRT5 is a mitochondrial deacylase with demalonylase activity, this finding suggests that acetylation can modulate the malonylome. Together, our results position acylations as an arm of the mitochondrial response to energy dysfunction and suggest a mechanism by which focal disruption to the energy production machinery can have an expanded impact on global mitochondrial function.

Long-term prognosis and genetic background of cardiomyopathy in 223 pediatric mitochondrial disease patients

BACKGROUND

Cardiomyopathy is a risk factor for poor prognosis in pediatric patients with mitochondrial disease. However, other risk factors including genetic factors related to poor prognosis in mitochondrial disease has yet to be fully elucidated.

METHODS AND RESULTS

Between January 2004 and September 2019, we enrolled 223 consecutive pediatric mitochondrial disease patients aged <18 years with a confirmed genetic diagnosis, including 114 with nuclear gene mutations, 89 patients with mitochondrial DNA (mtDNA) point mutations, 11 with mtDNA single large-scale deletions and 9 with chromosomal aberrations. Cardiomyopathy at baseline was observed in 46 patients (22%). Hazard ratios (HR) and 95% confidence intervals (CI) were calculated for all-cause mortality. Over a median follow-up of 36 months (12-77), there were 85 deaths (38%). The overall survival rate was significantly lower in patients with cardiomyopathy than in those without (p < 0.001, log-rank test). By multivariable analysis, left ventricular (LV) hypertrophy (HR = 4.6; 95% CI: 2.8-7.3), neonatal onset (HR = 2.9; 95% CI: 1.8-4.5) and chromosomal aberrations (HR = 2.9; 95% CI: 1.3-6.5) were independent predictors of all-cause mortality. Patients with LV hypertrophy with neonatal onset and/or chromosomal aberrations had higher mortality (100% in 21 patients) than those with LV hypertrophy alone (71% in 14 patients).

CONCLUSION

In pediatric patients with mitochondrial disease, cardiomyopathy was common (22%) and was associated with increased mortality. LV hypertrophy, neonatal onset and chromosomal aberrations were independent predictors of all-cause mortality. Prognosis is particularly unfavourable if LV hypertrophy is combined with neonatal onset and/or chromosomal aberrations.