Clinical and genetic correlate in childhood onset Friedreich ataxia

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.

Mitochondrial iron-sulfur cluster biogenesis from molecular understanding to clinical disease

Iron–sulfur clusters (ISCs) are known to play a major role in various protein functions. Located in the mitochondria, cytosol, endoplasmic reticulum and nucleus, they contribute to various core cellular functions. Until recently, only a few human diseases related to mitochondrial ISC biogenesis defects have been described. Such diseases include Friedreich ataxia, combined oxidative phosphorylation deficiency 19, infantile complex II/III deficiency defect, hereditary myopathy with lactic acidosis and mitochondrial muscle myopathy, lipoic acid biosynthesis defects, multiple mitochondrial dysfunctions syndromes and non ketotic hyperglycinemia due to glutaredoxin 5 gene defect. Disorders of mitochondrial import, export and translation, including sideroblastic anemia with ataxia, EVEN-PLUS syndrome and mitochondrial complex I deficiency due to nucleotide-binding protein-like protein gene defect, have also been implicated in ISC biogenesis defects. With advances in next generation sequencing technologies, more disorders related to ISC biogenesis defects are expected to be elucidated. In this article, we aim to shed the light on mitochondrial ISC biogenesis, related proteins and their function, pathophysiology, clinical phenotypes of related disorders, diagnostic approach, and future implications.

Childhood hereditary ataxias: experience from a tertiary referral university hospital in Turkey

Hereditary ataxias are a group of genetic disorders that are progressive and heterogeneous. The purpose of this study was to develop a practical and time-efficient approach to diagnosing childhood hereditary ataxias by analyzing characteristics and final diagnosis at a tertiary referral clinic for pediatric neurology. 196 patients admitted to the pediatric neurology department were included. The medical records were examined for demographic features, neurological, laboratory, electrophysiological, cranial imaging, and pathological findings, and for genetic studies. Patients were divided into two groups based on whether a final diagnosis was made. The undiagnosed and diagnosed groups consisted of 157 (81.1%) and 39 (19.9%) patients, respectively. The two groups differed in terms of levels of history of consanguineous marriage and mental and motor development before diagnosis, absence of deep tendon reflexes, and the presence of polyneuropathic changes detected by electromyelography (EMG), abnormal visual evoked potentials (VEPs), electroretinography (ERG), and muscle biopsy. To the best of our knowledge, this is the first study involving a large spectrum of diseases related to autosomal recessive ataxias in childhood in Turkey. One out of five patients with hereditary childhood ataxias can be diagnosed with clinical and laboratory and electrodiagnostic examination, especially with the help of imaging facilities, while genetic analysis is not possible for every child. Cranial magnetic resonance imaging followed by EMG provides the most important clues for the diagnosis of hereditary childhood ataxias.

Cardiac transplantation in Friedreich ataxia

In this article, we describe a 14-year-old boy with a confirmed diagnosis of Friedreich ataxia who underwent cardiac transplantation for left ventricular failure secondary to dilated cardiomyopathy with restrictive physiology. His neurological status prior to transplantation reflected early signs of neurological disease, with evidence of dysarthria, weakness, mild gait impairment, and limb ataxia. We review the ethical issues considered during the process leading to the decision to offer cardiac transplantation.

Friedreich ataxia presenting as sudden cardiac death in childhood: clinical, genetic and pathological correlation, with implications for genetic testing and counselling

Friedreich ataxia (FRDA) is the most common cause of childhood onset ataxia. We report on a 4 year old boy who suffered sudden cardiac death and was found to have a dilated cardiomyopathy with left ventricular hypertrophy on post-mortem studies. Molecular genetic testing subsequently confirmed the diagnosis of Friedreich ataxia. To our knowledge, this is the first report of Friedreich ataxia presenting as sudden cardiac death in early childhood.

Diagnosis and treatment of Friedreich ataxia: a European perspective

Friedreich ataxia is the most frequent hereditary ataxia, with an estimated prevalence of 3-4 cases per 100,000 individuals. This autosomal-recessive neurodegenerative disease is characterized by progressive gait and limb ataxia, dysarthria, lower-limb areflexia, decreased vibration sense, muscular weakness in the legs, and a positive extensor plantar response. Non-neurological signs include hypertrophic cardiomyopathy and diabetes mellitus. Symptom onset typically occurs around puberty, and life expectancy is 40-50 years. Friedreich ataxia is usually caused by a large GAA-triplet-repeat expansion within the first intron of the frataxin (FXN) gene. FXN mutations cause deficiencies of the iron-sulfur cluster-containing subunits of the mitochondrial electron transport complexes I, II, and III, and of the iron-sulfur protein aconitase. Mitochondrial dysfunction has been addressed in several open-label, non-placebo-controlled trials, which indicated that treatment with idebenone might ameliorate hypertrophic cardiomyopathy; a well-designed phase II trial suggested concentration-dependent functional improvements in non-wheelchair-bound children and adolescents. Other current experimental approaches address iron-mediated toxicity, or aim to increase FXN expression through the use of erythropoietin and histone deacetylase inhibitors. This Review provides guidelines, from a European perspective, for the diagnosis of Friedreich ataxia, differential diagnosis of ataxias and genetic counseling, and treatment of neurological and non-neurological symptoms.

Spinocerebellar ataxia type 7: a distinctive form of autosomal dominant cerebellar ataxia with retinopathy and marked genetic anticipation

When a child presents with progressive ataxia, there is a broad differential diagnosis and a very long list of potential investigations. Spinocerebellar ataxia type 7 presenting in infancy is a rare condition where a presumptive diagnosis can be made based on the clinical features alone. These include rapidly progressive ataxia, retinopathy and autosomal dominant inheritance with marked genetic anticipation of paternal origin. The father of the infant may manifest minimal symptoms at a time when the infant is severely affected. Diagnosis is confirmed by the demonstration of an expansion of a CAG repeat in the coding region of the gene on chromosome 3p. We present a case to illustrate the diagnostic difficulties. Antenatal diagnosis was performed in two subsequent pregnancies.

Friedreich's ataxia presenting after cardiac transplantation

A 4 year old boy underwent cardiac transplantation because of cardiomyopathy with ischaemia. Following transplantation he developed neurological signs of Friedreich's ataxia and the diagnosis was confirmed with genetic testing. Cardiomyopathy is a rare presentation of Friedreich's ataxia and to our knowledge this is the first reported transplant operation for the cardiomyopathy associated with this condition.