Friedreich's ataxia GAA repeat expansion in patients with recessive or sporadic ataxia

Emerging Therapies in Friedreich's Ataxia: A Review

Friedreich's ataxia (FRDA) is an inherited, neurodegenerative disease that typically presents in childhood and results in progressive gait and limb ataxia, with the extraneural features of hypertrophic cardiomyopathy, diabetes and scoliosis. The genetic defect results in a deficiency of frataxin protein, which is important for mitochondrial function, especially in the brain and heart. Drug development has approached FRDA through pathways addressing oxidative stress, mitochondrial dysfunction, frataxin protein deficiency and DNA transcriptional deficiency, paving the way for the first disease-modifying drugs for FRDA.

Friedreich's Ataxia Frequency in a Large Cohort of Genetically Undetermined Ataxia Patients

Background: Patients with suspected genetic ataxia are often tested for Friedreich's ataxia (FRDA) and/or a variety of spinocerebellar ataxias (SCAs). FRDA can present with atypical, late-onset forms and so may be missed in the diagnostic process. We aimed to determine FRDA-positive subjects among two cohorts of patients referred to a specialist ataxia centre either for FRDA or SCA testing to determine the proportion of FRDA cases missed in the diagnostic screening process. Methods: 2000 SCA-negative ataxia patients, not previously referred for FRDA testing (group A), were tested for FRDA expansions and mutations. This group was compared with 1768 ataxia patients who had been previously referred for FRDA testing (group B) and were therefore more likely to have a typical presentation. The phenotypes of positive cases were assessed through review of the clinical case notes. Results: Three patients (0.2%) in group A had the FRDA expansion on both alleles, compared with 207 patients (11.7%) in group B. The heterozygous carrier rate across both cohorts was of 41 out of 3,768 cases (1.1%). The size of the expansions in the three FRDA-positive cases in group A was small, and their presentation atypical with late-onset. Conclusions: This study demonstrates that FRDA is very rare among patients who were referred purely for SCA testing without the clinical suspicion of FRDA. Such cases should be referred to specialist ataxia centres for more extensive testing to improve patient management and outcomes.

Health related quality of life in Friedreich Ataxia in a large heterogeneous cohort

INTRODUCTION

This study assessed the Health Related Quality of Life (HRQOL) of individuals with Friedreich Ataxia (FRDA) through responses to HRQOL questionnaires.

METHODS

The SF-36, a generic HRQOL instrument, and symptom specific scales examining vision, fatigue, pain and bladder function were administered to individuals with FRDA and analyzed by comparison with disease features. Multiple linear regression models were used to study independent effects of genetic severity and age. Assessments were performed at baseline then intermittently after that.

RESULTS

Subjects were on average young adults. For the SF36, the subscale with the lowest HRQOL score was the physical function scale, while the emotional well-being score was the highest. The physical function scale correlated with age of onset, duration, and subject age. In assessment of symptom specific scales, bladder control scores (BLCS) correlated with duration and age, while impact of visual impairment scores (IVIS) correlated with duration. In linear regression models, the BLCS, Pain Effect Score, and IVIS scores were predicted by age and GAA length; modified fatigue impact scale scores were predicted only by GAA length. Physical function and role limitation scores declined over time. No change was seen over time in other SF-36 subscores. Symptom specific scales also worsened over time, most notably the IVIS and BLCS.

CONCLUSION

The SF-36 and symptom specific scales capture dysfunction in FRDA in a manner that reflects disease status. HRQOL dysfunction was greatest on physically related scales; such scales correlated with disease duration, indicating that they worsen with progressing disease.

Movement disorders in Friedreich's ataxia

Since the discovery of the gene mutation causing Friedreich's ataxia (FA), the rich spectrum of clinical manifestations of this autosomal recessive disorder is being increasingly recognized. Movement disorders besides ataxia, however, have not been fully characterized in patients with FA. We describe here two young male patients who, in addition to progressive ataxia, kinetic tremor and other typical features of FA, also manifest axial and limb dystonia. The primary purpose of this report is to draw attention to the broad spectrum of hyperkinetic movement disorders that can present as or be associated with FA.

Practical approaches to neurogenetic disease

Over the past 15 years, molecular genetic advances have led to new approaches for evaluation of neurogenetic disease. New diagnostic tests are available, and in some cases new diseases have been defined. However, effective use of these new tests still relies on solid clinical assessment to prioritize testing and interpret results. This review presents applications of genetic advances to a series of neurogenetic disorders, emphasizing the specific uses of genetic testing and the clinical questions that may arise. The rapid expansion in molecular diagnostics and genomics has fundamentally changed the approach to neurogenetic illnesses. Use of molecular biologic techniques has elucidated new disease mechanisms and allowed the application of genetic concepts to classically nongenetic illnesses. This has led to a wealth of new clinical information and created new dilemmas in patient care. In addition, it has brought into common usage a series of clinical genetic terms, such as variable expressivity (the range of phenotypic features in which the same disease can manifest) and anticipation (the progressively earlier age of onset of a specific disease in a family). This review provides a practical approach for neurogenetic evaluation of individuals who are likely to present in neuro-ophthalmologic practices with inherited ataxias, myotonic dystrophy, oculopharyngeal dystrophy, and Parkinson disease.

Friedreich's ataxia: treatment within reach

Friedreich's ataxia (FA) is the most prevalent cerebellar ataxia in children and adults in Europe. FA is one of a growing number of diseases known to be caused by triplet-repeat expansions. The causative mutation is a GAA trinucleotide-repeat expansion in the first intron of the frataxin gene. The mitochondrial localisation of frataxin and decreased oxidation activity in vivo and in vitro show that FA is a mitochondrial disease. Frataxin is involved in iron metabolism and may protect mitochondria from oxidative damage. The understanding of the disease has only just begun and possible treatments are within reach. In this review I discuss the clinical knowledge of FA and recent developments that have helped to elucidate the pathogenesis of the disease and made the first therapeutic attempts possible.

Spinocerebellar degenerations: an update

Over the past decade, the spinocerebellar degenerations have gone from a diverse group of loosely defined phenotypes to a family of diseases with many identifiable genotypes and the promise of gene-specific treatments. The evaluation of the spinocerebellar ataxias has been simplified, and the counseling of patients and families has been enhanced by the growing number of molecular diagnostic tests now available. Management strategies remain symptomatic and focused on rehabilitation, with empirical use of antioxidants based on research in other neurogenetic diseases.

Sequence variation in GAA repeat expansions may cause differential phenotype display in Friedreich's ataxia

Friedreich's ataxia, the most common autosomal recessive inherited ataxia, is characterized by progressive gait and limb ataxia. Friedreich's ataxia is known for its occurrence within the first or second decade of life and is associated with hypertrophic cardiomyopathy, and in some cases with diabetes. Genetically, it is identified by the expression of an unstable trinucleotide GAA repeat expansion located in the first intron of the X25 gene on chromosome 9. Two brothers with very late adult-onset ataxia, and their unaffected sister, were examined for the clinical presentation of FA and for the presence of the mutated FA gene. The relationship of the expanded gene sequence to the severity of disease and age of onset were evaluated. Clinical examination revealed that the two brothers had mild ataxia and proprioceptive loss, with age of onset between 60 and 70 years of age. DNA from peripheral blood nucleated cells demonstrated a small homozygous expansion, with approximately 120-130 GAA repeats in the X25 gene in both patients. The expanded repeats were interrupted either with GAAGAG, GAAGGA, or GAAGAAAA sequences. The unaffected sister carried a normal FA genotype with 8-uninterrupted GAA repeat, observed by sequence analysis. In addition, the levels of FA gene transcript in both brothers were relatively lower than that in the unaffected sister. No detectable cardiomyopathy or diabetes was observed. Phenotypic diversity of FA is increasingly expanding. The age of onset and the structure of GAA repeat expansion plays an important role in determining the clinical features and the differential diagnosis of FA. The confirmation of the FA gene mutation in the atypical case, broadens the clinical spectrum of FA, and supports the idea that patients with even a mild form of ataxia of late adult onset should be considered for molecular testing.

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.

Molecular Genetics and Inherited Ataxias: Redefining Phenotypes and Pathogenesis

Genetic research on inherited ataxias has transformed our understanding of these conditions. The availability of genetic testing has shown that a classification based solely on clinical and pathologic findings is not adequate, and molecular genetic analysis is now mandatory for diagnostic accuracy and prognostic purposes. The epidemiology of these disorders is also being rewritten under the light of molecular genetic analysis. In this review, we discuss some of the recent advances on the hereditary cerebellar degenerations without a known metabolic defect, focusing on genotype-phenotype correlations in the spinocerebellar ataxias (SCAs) and Friedreich’s ataxia (FRDA). Three main biochemical pathways seem to be involved in the pathogenesis of inherited ataxias: 1) expansion of (CAG)n repeats within genes coding for polyglutamine-containing proteins (SCAs); 2) impairment of mitochondrial function (FRDA); and 3) dysfunction of ion channels (episodic ataxias, EA1, EA2). It is likely that many neurodegenerative conditions will prove to share basic molecular mechanisms, and therefore, data provided by the investigation of a particular disease is likely to be relevant to our global understanding of spinocerebellar degenerations and other degenerative disorders of the nervous system. A better knowledge of the molecular and cellular routes leading to neurodegeneration will provide a key to the design of rational therapies.

Clinical and genetic aspects of spinocerebellar degeneration

After decades of confusion as a result of the marked clinical variability of spinocerebellar degeneration, molecular analyses have permitted the identification of loci and genes, which constitute the basis of a new classification. However, even greater genetic heterogeneity is suspected and several phenotypes, such as complex forms of spastic paraplegia and autosomal recessive ataxias, have not yet been thoroughly explored. Unexpectedly, the genes responsible for Friedreich's ataxia and a form of autosomal recessive spastic paraplegia place these diseases in the category of mitochondrial disorders. The unstable mutations caused by trinucleotide repeat expansions are responsible for a growing number of inherited cerebellar ataxias.

Unique origin and specific ethnic distribution of the Friedreich ataxia GAA expansion

The GAA triplet repeat expansion that causes Friedreich ataxia is found only in individuals of European, North African, Middle Eastern, or Indian origin (Indo-European and Afro-Asiatic speakers). Analysis of normal alleles of the GAA repeat and of closely linked markers suggests that expansions arose through a unique two-step process. A major implication of these findings is that Friedreich ataxia may not exist among sub-Saharan Africans, Amerindians, and people from China, Japan, and Southeast Asia.

A nonpathogenic GAAGGA repeat in the Friedreich gene: implications for pathogenesis

An individual with late-onset ataxia was found to be heterozygous for an unusual (GAAGGA)65 sequence and a normal GAA repeat in the frataxin gene. No frataxin point mutation was present, excluding a form of Friedreich ataxia. (GAAGGA)65 did not have the inhibitory effect on gene expression in transfected cells shown by pathogenic GAA repeats of similar length. GAA repeats, but not (GAAGGA)65, adopt a triple helical conformation in vitro. We suggest that such a triplex structure is essential for suppression of gene expression.

Molecular genetics and pathogenesis of Friedreich ataxia

Friedreich ataxia, the most frequent cause of inherited ataxia, is due in most cases to a large expansion of an intronic GAA repeat, resulting in decreased expression of the target frataxin gene. The autosomal recessive inheritance of the disease gives this triplet repeat mutation some unique features of natural history and evolution. Frataxin is a mitochondrial protein that has homologues in yeast and even in gram negative bacteria. Yeast deficient in the frataxin homologue accumulate iron in mitochondria and show increased sensitivity to oxidative stress. This suggests that Friedreich ataxia is caused by mitochondrial dysfunction and free radical toxicity.