Myocardial Perfusion Reserve in Children with Friedreich Ataxia

A global perspective on research advances and future challenges in Friedreich ataxia

Friedreich ataxia (FRDA) is a rare multisystem, life-limiting disease and is the most common early-onset inherited ataxia in populations of European, Arab and Indian descent. In recent years, substantial progress has been made in dissecting the pathogenesis and natural history of FRDA, and several clinical trials have been initiated. A particularly notable recent achievement was the approval of the nuclear factor erythroid 2-related factor 2 activator omaveloxolone as the first disease-specific therapy for FRDA. In light of these developments, we review milestones in FRDA translational and clinical research over the past 10 years, as well as the various therapeutic strategies currently in the pipeline. We also consider the lessons that have been learned from failed trials and other setbacks. We conclude by presenting a global roadmap for future research, as outlined by the recently established Friedreich's Ataxia Global Clinical Consortium, which covers North and South America, Europe, India, Australia and New Zealand.

Characterization of clinical serum cardiac biomarker levels in individuals with Friedreich ataxia

Friedreich ataxia is a progressive autosomal recessive neurodegenerative disorder characterized by ataxia, dyscoordination, and cardiomyopathy. A subset of patients with Friedreich ataxia have elevated levels of serum cardiac troponin I, but associations with disease outcomes and features of cardiomyopathy remain unclear. In this study, we characterized clinically obtained serum cardiac biomarker levels including troponin I, troponin T, and B-type natriuretic peptide in subjects with Friedreich ataxia and evaluated their association with markers of disease. While unprovoked troponin I levels were elevated in 36% of the cohort, cTnI levels associated with a cardiac event (provoked) were higher than unprovoked levels. In multivariate linear regression models, younger age predicted increased troponin I values, and in logistic regression models younger age, female sex, and marginally longer GAA repeat length predicted abnormal troponin I levels. In subjects with multiple assessments, mean unprovoked troponin I levels decreased slightly over time. The presence of abnormal troponin I values and their levels were predicted by echocardiographic measures of hypertrophy. In addition, troponin I levels predicted long-term markers of clinical cardiac dysfunction over time to a modest degree. Consequently, troponin I values provide a marker of hypertrophy but only a minimally predictive biomarker for later cardiac manifestations of disease such as systolic dysfunction or arrhythmia.

Cardiovascular Research in Friedreich Ataxia: Unmet Needs and Opportunities

Friedreich Ataxia (FRDA) is an autosomal recessive disease in which a mitochondrial protein, frataxin, is severely decreased in its expression. In addition to progressive ataxia, patients with FRDA often develop a cardiomyopathy that can be hypertrophic. This cardiomyopathy is unlike the sarcomeric hypertrophic cardiomyopathies in that the hypertrophy is associated with massive mitochondrial proliferation within the cardiomyocyte rather than contractile protein overexpression. This is associated with atrial arrhythmias, apoptosis, and fibrosis over time, and patients often develop heart failure leading to premature death. The differences between this mitochondrial cardiomyopathy and the more common contractile protein hypertrophic cardiomyopathies can be a source of misunderstanding in the management of these patients. Although imaging studies have revealed much about the structure and function of the heart in this disease, we still lack an understanding of many important clinical and fundamental molecular events that determine outcome of the heart in FRDA. This review will describe the current basic and clinical understanding of the FRDA heart, and most importantly, identify major gaps in our knowledge that represent new directions and opportunities for research.