Cardiomyopathy in Friedreich ataxia: exemplifying the challenges faced by cardiologists in the management of rare diseases

Early onset development of hypertrophic cardiomyopathy in less than 1 year in a patient with familial Friedrich's ataxia: Case report

Friedreich's ataxia (FRDA) is a neurodegenerative disease characterized by progressive ataxia, dysarthria, sensory loss. While neurological symptoms are prominent, cardiac manifestations significantly contribute to mortality. Cardiomyopathy in Friedreich's disease results from mitochondrial dysfunction, loss of contractile proteins and an accumulation of fibrosis in heart. To better characterize the severity of cardiac involvement, the MICONOS study group developed a classification system categorizing FRDA cardiomyopathy as "no," "mild," "intermediate," "severe." We report an uncommon case of early-onset development of hypertrophic cardiomyopathy (HCM) in a 25-year-old female diagnosed with Friedreich's ataxia (FRDA) at age 12. Through annual cardiac evaluations, no signs of cardiac disease were noted. Until presenting with dyspnea and palpitations. Clinical examination revealed truncal ataxia and dysarthria, but no signs of heart failure. However, a transthoracic echocardiography demonstrated nonobstructive hypertrophic cardiomyopathy with a maximal wall thickness of 20 mm, incomplete anterior systolic motion of the mitral valve, a significant development in less than 1 year after last normal cardiac assessment. Left ventricular systolic function was preserved (ejection fraction 50%). She was prescribed bisoprolol and dapagliflozin, with significant improvement at her latest checkup. Family screening revealed HCM in her 30 year female sibling, who also has FRDA. No cardiac abnormalities were detected in her younger brother or parents. Friedreich's hypertrophic cardiomyopathy has been reported as the most significant cause of mortality, especially among younger patients with early onset disease manifestations.

Brain microvascular endothelial cells differentiated from a Friedreich's Ataxia patient iPSC are deficient in tight junction protein expression and paracellularly permeable

Friedreich's Ataxia (FA) is a rare, inherited ataxia resulting from GAA triplet expansions in the first intron of the Frataxin (FXN) gene, which encodes a mitochondrial protein involved in the incorporation of iron into iron-sulfur clusters. We previously identified decreased levels of F-actin and tight junction (TJ) proteins, which coincided with paracellular permeability in an FXN shRNA-mediated knockdown immortalized human brain microvascular endothelial cell (BMVEC) model. This premise is underexplored in the FA literature, prompting us to confirm these findings using a patient-derived iPSC model. One line each of FA patient iPSCs and age- and sex-matched apparently healthy iPSCs were differentiated into BMVEC-like cells. We quantified actin glutathionylation, F-actin abundance, TJ expression and organization, and barrier integrity. In the absence of dysregulated F-actin organization, FA iBMVEC exhibited a loss of 50% ZO-1, 63% Occludin, and 19% Claudin-5 protein expression, along with a disruption in the bi-cellular organization of the latter two proteins. Functionally, this correlated with barrier hyperpermeability, delayed barrier maturation, and increased flux of the fluorescent tracer Lucifer Yellow. These data indicate that decreased barrier integrity is a pathophysiological phenotype of FA brain microvascular endothelial cells. Clinically, this may represent a targetable pathway to reduce brain iron accumulation, neuroinflammation, and neurodegeneration profiles in FA. Additionally, an investigation into other barrier systems, such as the blood-nerve barrier, blood-CSF barrier, or cardiac vasculature, may provide insights into the extra-neural symptoms experienced by FA patients.

Precision medicine and Friedreich ataxia: promoting equity, beneficence, and informed consent for novel gene therapies

Friedreich Ataxia (FA) is an incurable neurodegenerative disease with systemic consequences affecting vital organs including those of the central and peripheral nervous systems. This article will use FA as an example to explore some of the practical and ethical issues emerging in precision medicine for rare diseases. It will first describe the existing management strategies available for FA patients, before considering the potential impact of gene therapy trials on the prevention and treatment of disease symptoms. Finally, ethical considerations will be discussed, including equity of access and managing resource allocation dilemmas; balancing benefits, burdens and harms; and gaining informed consent for novel treatments.

AAV8 gene therapy reverses cardiac pathology and prevents early mortality in a mouse model of Friedreich's ataxia

Friedreich's ataxia (FRDA) is an autosomal-recessive disorder primarily attributed to biallelic GAA repeat expansions that reduce expression of the mitochondrial protein frataxin (FXN). FRDA is characterized by progressive neurodegeneration, with many patients developing cardiomyopathy that progresses to heart failure and death. The potential to reverse or prevent progression of the cardiac phenotype of FRDA was investigated in a mouse model of FRDA, using an adeno-associated viral vector (AAV8) containing the coding sequence of the FXN gene. The Fxnflox/null::MCK-Cre conditional knockout mouse (FXN-MCK) has an FXN gene ablation that prevents FXN expression in cardiac and skeletal muscle, leading to cardiac insufficiency, weight loss, and morbidity. FXN-MCK mice received a single intravenous injection of an AAV8 vector containing human (hFXN) or mouse (mFXN) FXN genes under the control of a phosphoglycerate kinase promoter. Compared to vehicle-treated FXN-MCK control mice, AAV-treated FXN-MCK mice displayed increases in body weight, reversal of cardiac deficits, and increases in survival without apparent toxicity in the heart or liver for up to 12 weeks postdose. FXN protein expression in heart tissue was detected in a dose-dependent manner, exhibiting wide distribution throughout the heart similar to wild type, but more speckled. These results support an AAV8-based approach to treat FRDA-associated cardiomyopathy.

Genome-wide enhancer-associated tandem repeats are expanded in cardiomyopathy

BACKGROUND

Cardiomyopathy is a clinically and genetically heterogeneous heart condition that can lead to heart failure and sudden cardiac death in childhood. While it has a strong genetic basis, the genetic aetiology for over 50% of cardiomyopathy cases remains unknown.

METHODS

In this study, we analyse the characteristics of tandem repeats from genome sequence data of unrelated individuals diagnosed with cardiomyopathy from Canada and the United Kingdom (n = 1216) and compare them to those found in the general population. We perform burden analysis to identify genomic and epigenomic features that are impacted by rare tandem repeat expansions (TREs), and enrichment analysis to identify functional pathways that are involved in the TRE-associated genes in cardiomyopathy. We use Oxford Nanopore targeted long-read sequencing to validate repeat size and methylation status of one of the most recurrent TREs. We also compare the TRE-associated genes to those that are dysregulated in the heart tissues of individuals with cardiomyopathy.

FINDINGS

We demonstrate that tandem repeats that are rarely expanded in the general population are predominantly expanded in cardiomyopathy. We find that rare TREs are disproportionately present in constrained genes near transcriptional start sites, have high GC content, and frequently overlap active enhancer H3K27ac marks, where expansion-related DNA methylation may reduce gene expression. We demonstrate the gene silencing effect of expanded CGG tandem repeats in DIP2B through promoter hypermethylation. We show that the enhancer-associated loci are found in genes that are highly expressed in human cardiomyocytes and are differentially expressed in the left ventricle of the heart in individuals with cardiomyopathy.

INTERPRETATION

Our findings highlight the underrecognized contribution of rare tandem repeat expansions to the risk of cardiomyopathy and suggest that rare TREs contribute to ∼4% of cardiomyopathy risk.

FUNDING

Government of Ontario (RKCY), The Canadian Institutes of Health Research PJT 175329 (RKCY), The Azrieli Foundation (RKCY), SickKids Catalyst Scholar in Genetics (RKCY), The University of Toronto McLaughlin Centre (RKCY, SM), Ted Rogers Centre for Heart Research (SM), Data Sciences Institute at the University of Toronto (SM), The Canadian Institutes of Health Research PJT 175034 (SM), The Canadian Institutes of Health Research ENP 161429 under the frame of ERA PerMed (SM, RL), Heart and Stroke Foundation of Ontario & Robert M Freedom Chair in Cardiovascular Science (SM), Bitove Family Professorship of Adult Congenital Heart Disease (EO), Canada Foundation for Innovation (SWS, JR), Canada Research Chair (PS), Genome Canada (PS, JR), The Canadian Institutes of Health Research (PS).

How can we use stem cell-derived cardiomyocytes to understand the involvement of energetic metabolism in alterations of cardiac function?

Mutations in the mitochondrial-DNA or mitochondria related nuclear-encoded-DNA lead to various multisystemic disorders collectively termed mitochondrial diseases. One in three cases of mitochondrial disease affects the heart muscle, which is called mitochondrial cardiomyopathy (MCM) and is associated with hypertrophic, dilated, and noncompact cardiomyopathy. The heart is an organ with high energy demand, and mitochondria occupy 30%-40% of its cardiomyocyte-cell volume. Mitochondrial dysfunction leads to energy depletion and has detrimental effects on cardiac performance. However, disease development and progression in the context of mitochondrial and nuclear DNA mutations, remains incompletely understood. The system of induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CM) is an excellent platform to study MCM since the unique genetic identity to their donors enables a robust recapitulation of the predicted phenotypes in a dish on a patient-specific level. Here, we focus on recent insights into MCM studied by patient-specific iPSC-CM and further discuss research gaps and advances in metabolic maturation of iPSC-CM, which is crucial for the study of mitochondrial dysfunction and to develop novel therapeutic strategies.

The cardiomyopathy of Friedreich's ataxia common in a family: A case report

Introduction and importance

Friedreich's Ataxia is an autosomal recessive disease and is usually associated with arterial dysfunction, muscle weakness, spasm in the lower extremities, scoliosis, bladder dysfunction, lack of reflexes in the lower extremities, and imbalance. Approximately 2.3 people have cardiomyopathy. In this article, we have reviewed a case of Friedreich's Ataxia with hypertrophic cardiomyopathy.

Case presentation

A 19-year-old woman with Friedreich's Ataxia has been protesting since she was 11 years old and complained of chest pains, dyspnea, and heart palpitations without a medical history. In ECG, Asymmetrical invert T wave diffuse, diffuse ST-segment depression, and left ventricular hypertrophy were observed. In echocardiography, the left ventricle was reported as hyperimmobile with increased EF (70-75%).

Clinical discussion

In the present study, a patient with Friedrich Ataxia was diagnosed with chest pain, dyspnea, and palpitations without any medical history, and was discharged from the hospital after treatment. In the patients introduced and our patient, there was significant fibro-myocardial hypertrophy, in which the ventricular septal hypertrophy was marked by hypertrophic cardiomyopathy.

Conclusion

Because early diagnosis of the disease is difficult, clinical signs and the patient's current profile at the time of referral will be very helpful.

Cardiovascular Manifestations of Mitochondrial Disease

Genetic mitochondrial cardiomyopathies are uncommon causes of heart failure that may not be seen by most physicians. However, the prevalence of mitochondrial DNA mutations and somatic mutations affecting mitochondrial function are more common than previously thought. In this review, the pathogenesis of genetic mitochondrial disorders causing cardiovascular disease is reviewed. Treatment options are presently limited to mostly symptomatic support, but preclinical research is starting to reveal novel approaches that may lead to better and more targeted therapies in the future. With better understanding and clinician education, we hope to improve clinician recognition and diagnosis of these rare disorders in order to improve ongoing care of patients with these diseases and advance research towards discovering new therapeutic strategies to help treat these diseases.

Circulating miR-323-3p is a biomarker for cardiomyopathy and an indicator of phenotypic variability in Friedreich's ataxia patients

MicroRNAs (miRNAs) are noncoding RNAs that contribute to gene expression modulation by regulating important cellular pathways. In this study, we used small RNA sequencing to identify a series of circulating miRNAs in blood samples taken from Friedreich’s ataxia patients. We were thus able to develop a miRNA biomarker signature to differentiate Friedreich’s ataxia (FRDA) patients from healthy people. Most research on FDRA has focused on understanding the role of frataxin in the mitochondria, and a whole molecular view of pathological pathways underlying FRDA therefore remains to be elucidated. We found seven differentially expressed miRNAs, and we propose that these miRNAs represent key mechanisms in the modulation of several signalling pathways that regulate the physiopathology of FRDA. If this is the case, miRNAs can be used to characterize phenotypic variation in FRDA and stratify patients’ risk of cardiomyopathy. In this study, we identify miR-323-3p as a candidate marker for phenotypic differentiation in FRDA patients suffering from cardiomyopathy. We propose the use of dynamic miRNAs as biomarkers for phenotypic characterization and prognosis of FRDA.