Investigation of recessive ataxia loci in patients with young age of onset

Autosomal recessive cerebellar ataxias are a phenotypically and genetically heterogeneous group of diseases. Major forms can be distinguished on the basis of clinical signs, age of onset, biochemical parameters or genotypes. To develop rational diagnostic strategies, phenotypic information, e.g., age of onset combined with population-specific disease frequencies could be highly favourable. We tested this hypothesis for single candidate loci and mutations in North European ataxia patients with juvenile and early adult onset. While we could prove that Friedreich ataxia (FRDA) is frequent in Germany, only few patients with ataxia-oculomotor apraxia type 1 (AOA1) and type 2 (AOA2) were diagnosed. The frequency of the mitochondrial recessive ataxia syndrome (MIRAS) and the infantile onset spinocerebellar ataxia (IOSCA) in this population remains unknown since no case with the common mutation of the corresponding gene was detected.     

Frataxin gene point mutations in Italian Friedreich ataxia patients

Friedreich ataxia (FRDA) is associated with a GAA-trinucleotide-repeat expansion in the first intron of the FXN gene (9q13-21), which encodes a 210-amino-acid protein named frataxin. More than 95% of patients are homozygous for 90-1,300 repeat expansion on both alleles. The remaining patients have been shown to be compound heterozygous for a GAA expansion on one allele and a micromutation on the other. The reduction of both frataxin messenger RNA (mRNA) and protein was found to be proportional to the size of the smaller GAA repeat allele. We report a clinical and molecular study of 12 families in which classical FRDA patients were heterozygous for a GAA expansion on one allele. Sequence analysis of the FXN gene allowed the identification of the second disease-causing mutation in each heterozygous patient, which makes this the second largest series of FRDA compound heterozygotes reported thus far. We have identified seven mutations, four of which are novel. Five patients carried missense mutations, whereas eight patients carried null (frameshift or nonsense) mutations. Quantitation of frataxin levels in lymphoblastoid cell lines derived from six compound heterozygous patients showed a statistically significant correlation of residual protein levels with the age at onset (r = 0.82, p < 0.05) or the GAA expansion (r = -0.76, p < 0.1). In the group of patients heterozygous for a null allele, a strong (r = -0.94, p < 0.01) correlation was observed between the size of GAA expansion and the age at onset, thus lending support to the hypothesis that the residual function of frataxin in patients' cells derive exclusively from the expanded allele.     

Frataxin point mutations in two patients with Friedreich's ataxia and unusual clinical features

Two patients with a progressive ataxia are presented with clinical features consistent with classic Friedreich's ataxia (FRDA), but also with features unusual for FRDA. Analysis of DNA showed that each patient is heterozygous for the expanded GAA repeat of FRDA, but carries a base change on his other frataxin allele. For one patient a non-conservative arginine to cysteine amino acid change is predicted at amino acid 165 whereas the other mutation is found at the junction of exon one and intron one. Muscle biopsy showed an absence of frataxin immunoreactivity in the patient harbouring the intronic mutation, confirming the pathological nature of the base change. These mutations extend the range of point mutations seen in FRDA, and agree with recent reports suggesting phenotypic variation in patients with FRDA harbouring point mutations in conjunction with an expanded GAA repeat.     

Variations of frataxin protein levels in normal individuals

Friedreich’s ataxia (FRDA) is the most common of the inherited ataxias and is associated with GAA trinucleotide repeat expansions within the first intron of the frataxin (FXN) gene. There are expanded FXN alleles from 66 to 1,700 GAA·TTC repeats in FRDA patients and correlations between number of GAA repeats and frataxin protein levels are assumed. Here, we present for the first time frataxin protein levels as well as analysis of GAA triplet repeats in the FXN gene in a population of 50 healthy Austrian people. Frataxin protein levels were measured in lymphocytes from blood samples by ELISA and GAA repeats were analyzed by capillary electrophoresis. Rather unexpectedly, we found a high variation of frataxin protein levels among the individuals. In addition, there was no correlation between frataxin levels, GAA repeats, age and sex in this group. However, these findings are of great importance for better characterization of the disease.     

Molecular analysis of Friedreich's ataxia locus in the Indian population

OBJECTIVES: Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by expansion of GAA repeats in the frataxin gene. We have carried out the first molecular analysis at the Friedreich's ataxia locus in the Indian population. MATERIALS AND METHODS: Three families clinically diagnosed for Friedreich's ataxia were analyzed for GAA expansion at the FRDA locus. The distribution of GAA repeats was also estimated in normal individuals of Indian origin. RESULTS: All patients clinically diagnosed for Friedreich's ataxia were found to be homozygous for GAA repeat expansion. The GAA repeat in the normal population show a bimodal distribution with 94% of alleles ranging from 7-16 repeats. CONCLUSION: Indian patients with expansion at the FRDA locus showed typical clinical features of Friedreich's ataxia. The low frequency of large normal alleles (6%) could indicate that the prevalence of this disease in the Indian population is likely to be low.     

miR-886-3p levels are elevated in Friedreich ataxia

Friedreich ataxia (FRDA) is the most common inherited ataxia caused primarily by an intronic GAA.TTC triplet repeat expansion in the frataxin (FXN) gene. FXN RNA and protein levels are reduced in patients leading to progressive gait and limb ataxia, sensory loss, reduced tendon reflexes, dysarthria, absent lower limb reflexes, and loss of position and vibration sense. Neurological manifestations ensue from primary loss of dorsal root ganglia neurons and their associated axons ascending centrally in the spinal cord and peripherally in large myelinated nerves. Small noncoding RNAs such as microRNAs have been shown to be dysregulated in neurodegenerative diseases such as Alzheimer's and Huntington's disease. Here we report that hsa-miR-886-3p (miR-886-3p) was increased in patient cells as well as peripheral patient blood samples. Selective reduction in miR-886-3p by an anti-miR led to elevation of FXN message and protein levels without associated changes in histone marks at the FXN locus. Nevertheless, derepression of frataxin by a histone deacetylase inhibitor leads to a decrease in miR-886-3p. These results outline involvement of a small RNA, miR-886-3p in FRDA and a novel therapeutic approach to this disease using an anti-miR-886-3p.     

Prolonged treatment with pimelic o-aminobenzamide HDAC inhibitors ameliorates the disease phenotype of a Friedreich ataxia mouse model

Friedreich ataxia (FRDA) is an inherited neurodegenerative disorder caused by GAA repeat expansion within the FXN gene, leading to epigenetic changes and heterochromatin-mediated gene silencing that result in a frataxin protein deficit. Histone deacetylase (HDAC) inhibitors, including pimelic o-aminobenzamide compounds 106, 109 and 136, have previously been shown to reverse FXN gene silencing in short-term studies of FRDA patient cells and a knock-in mouse model, but the functional consequences of such therapeutic intervention have thus far not been described. We have now investigated the long-term therapeutic effects of 106, 109 and 136 in our GAA repeat expansion mutation-containing YG8R FRDA mouse model. We show that there is no overt toxicity up to 5 months of treatment and there is amelioration of the FRDA-like disease phenotype. Thus, while the neurological deficits of this model are mild, 109 and 106 both produced an improvement of motor coordination, whereas 109 and 136 produced increased locomotor activity. All three compounds increased global histone H3 and H4 acetylation of brain tissue, but only 109 significantly increased acetylation of specific histone residues at the FXN locus. Effects on FXN mRNA expression in CNS tissues were modest, but 109 significantly increased frataxin protein expression in brain tissue. 109 also produced significant increases in brain aconitase enzyme activity, together with reduction of neuronal pathology of the dorsal root ganglia (DRG). Overall, these results support further assessment of HDAC inhibitors for treatment of Friedreich ataxia.     

Friedreich’s ataxia: clinical heterogeneity in two sisters

Abstract Diagnostic evaluation of two sisters affected by ataxia, with similar age of onset, revealed a characteristic trinucleotide expansion in the Friedreich’s ataxia (FRDA) locus and two different phenotypic presentations. At onset the elder sister had retained deep tendon reflexes (FARR), while the younger sister presented classic FRDA. The GAA expansion in the patients’ alleles proved to be similar in both siblings, ruling out that age at onset and clinical heterogeneity could be due to different FRDA mutations. On the whole, clinical and genetic data on these patients confirmed that FARR is a variant phenotype of FRDA.     

Frequency analysis and clinical characterization of different types of spinocerebellar ataxia in Serbian patients.

The relative frequencies of different spinocerebellar ataxias (SCAs) vary widely among different ethnic groups, presumably due to a founder effect. We investigated the relative prevalence of SCA1-3, 6-8, 12, 17; dentate-rubro-pallidoluysian atrophy; and Friedreich's ataxia (FRDA) in Serbian patients with adult-onset (>20 years of age) hereditary and sporadic SCAs, and compared clinical features of patients with genetically confirmed SCAs. A total of 108 patients from 54 families (38 apparently dominant [ADCA] and 16 apparently recessive) with adult-onset hereditary ataxia and 75 apparently sporadic patients were assessed. Of 38 families with ADCA, 13 (34%) were positive for an expansion in an SCA1 and 5 families (13%) for an expansion in an SCA2 allele. In 20 families (53%), no expansions have been identified in any of the analyzed genes. Gaze palsy, spasticity, and hyperreflexia were significantly more common in SCA1, whereas slow saccades, hypotonia, hyporeflexia, and dystonia prevailed in SCA2 patients. Among the 16 families with an apparently recessive mode of ataxia inheritance, 4 (25%) were identified as having the FRDA mutation. Ataxia-causing mutations were identified in 8 (10.6%) of patients with apparently sporadic adult-onset ataxia.     

Clinical and molecular studies in five Brazilian cases of Friedreich ataxia.

Friedreich ataxia (FRDA), the most common autosomal recessive ataxia, is caused in 94% of cases by homozygous expansions of an unstable GAA repeat localised in intron 1 of the X25 gene. We have investigated this mutation in five Brazilian patients: four with typical FRDA findings and one patient with atypical manifestations, who was considered to have some other form of cerebellar ataxia with retained reflexes. The GAA expansion was detected in all these patients. The confirmation of FRDA diagnosis in the atypical case may be pointing out, as in other reports, that clinical spectrum of Friedreich's ataxia is broader than previously recognised and includes cases with intact tendon reflexes.     

Gene Expression Profile in Peripheral Blood Cells of Friedreich Ataxia Patients

Friedreich ataxia (FRDA) is the most common autosomal recessive ataxia characterized by a combination of neurological involvement, cardiomyopathy, and skeletal and glucose metabolism disturbances. FRDA is caused by mutations in FXN gene that results in reduction of mRNA and protein levels of frataxin. Previous microarray and real-time quantitative PCR (qPCR) studies showed that the downregulation of FXN is associated with a complex gene expression profile. However, these studies showed a wide variability in the subset of genes with altered expression among tissues and models. Genes differentially expressed in peripheral blood cells (PBC) could potentially help in the understanding of FRDA pathophysiology and also function as reliable disease biomarkers obtained from an easily accessible tissue, which could have implications in clinical practice. This study aimed to validate by qPCR the expression of 26 genes, revealed as differentially expressed by other studies, using peripheral blood cells (PBC) of 11 FRDA patients compared to 11 healthy controls. We found a robust downregulation of FXN, but no statistically significant differences were found between FRDA and controls for the remaining genes. Except for FXN, our study did not find a differential gene expression profile in PBC of FRDA patients and a reliable gene expression profile biomarker in a clinical relevant and noninvasive tissue remains unclear.     

Friedreich's ataxia and other hereditary ataxias in Greece: An 18-year perspective

Limited data exist on the spectrum of heredoataxias in Greece, including the prevalence and phenotype of Friedreich's ataxia (FRDA) and the prevalence and subtypes of dominant spinocerebellar ataxias (SCAs). We analyzed clinically and investigated genetically for FRDA and triplet-repeat expansion SCAs a consecutive series of 186 patients with suspected heredoataxia referred to Athens over 18 years. For prevalence estimates we included patients with molecular diagnosis from Cyprus that were absent from the Athens cohort. The minimum prevalence of FRDA was ~ 0.9/100,000, with clusters of high prevalence in Aegean islands. FRDA was diagnosed in 73 probands. The genotypic and phenotypic spectrum of FRDA was similar to other populations, with one patient compound heterozygote for a known point mutation in FXN (Asn146Lys). Undiagnosed recessive ataxias included FRDA-like and spastic ataxias. The minimum prevalence of dominant SCAs was ~ 0.7/100,000. SCA1 (4), SCA7 (4), SCA2, SCA6, and SCA17 (1 each) probands were identified. A molecular diagnosis was reached in 31% of dominant cases. Undiagnosed dominant patients included a majority of type III autosomal dominant cerebellar ataxias. FRDA is the commonest heredoataxia in the Greek population with prevalence towards the lower end of other European populations. Dominant SCAs are almost as prevalent. SCA1, SCA2, SCA6, SCA7 and SCA17 patients complete the spectrum of cases with a specific molecular diagnosis.     

Clinical use of frataxin measurement in a patient with a novel deletion in the FXN gene

Friedreich ataxia (FRDA) is caused by a GAA expansion in the first intron of the FXN gene, which encodes frataxin. Four percent of patients harbor a point mutation on one allele and a GAA expansion on the other. We studied an Italian patient presenting with symptoms suggestive of FRDA, and carrying a single expanded 850 GAA allele. As a second diagnostic step, frataxin was measured in peripheral blood mononuclear cells, and proved to be in the pathological range (2.95 pg/μg total protein, 12.7 % of control levels). Subsequent sequencing revealed a novel deletion in exon 5a (c.572delC) which predicted a frameshift at codon 191 and a premature truncation of the protein at codon 194 (p.T191IfsX194). FXN/mRNA expression was reduced to 69.2 % of control levels. Clinical phenotype was atypical with absent dysarthria, and rapid disease progression. l-Buthionine-sulphoximine treatment of the proband’s lymphoblasts showed a severe phenotype as compared to classic FRDA.     

Locus heterogeneity in Friedreich ataxia

Friedreich ataxia (FRDA) is the most common form of autosomal recessive ataxia. The disease locus was assigned to chromosome 9 and the disease gene, STM7/X25, has been isolated. To date most data suggest locus homogeneity in FRDA. We now provide strong evidence of a second FRDA locus. Studying two siblings with FRDA from two families we did not detect a mutation in STM7/X25. Haplotype analysis of the STM7/X25 region of chromosome 9 demonstrated that the relevant portion of chromosome 9 differs in the patients. Although the patients studied had typical FRDA, one sibpair had the uncommon symptom of retained tendon reflexes. In order to investigate whether retained tendon reflexes are characteristic of FRDA caused by the second locus, FRDA2, we studied an unrelated FRDA patient with retained tendon reflexes. The observation of typical mutations in STM7/X25 (GAA exopansions) in this patient demonstrates that the two genetically different forms of FRDA cannot be distinguished clinically. Received December 19, 1996; Revised and Accepted January 22, 1997     

Malaysian siblings with friedreich ataxia and chorea: a novel deletion in the frataxin gene

BACKGROUND: Friedrich ataxia (FRDA1) is most often the result of a homozygous GAA repeat expansion in the first intron of the frataxin gene (FRDA gene). This condition is seen in individuals of European, North African, Middle Eastern and Indian descent and has not been reported in Southeast Asian populations. Approximately 4% of FRDA1 patients are compound heterozygotes. These patients have a GAA expansion on one allele and a point mutation on the other and have been reported to have an atypical phenotype. OBJECTIVE: To describe a novel dinucleotide deletion in the FRDA gene in two Malaysian siblings with FRDA1. SETTING: Tertiary referral university hospital setting. PATIENTS AND METHODS: A previously healthy 10-year-old Malaysian boy, presented with fever, lethargy, headaches, dysarthria, dysphagia, vertigo and ataxia which developed over a one week period. His neurological exam revealed evidence of dysarthria and ataxia, mild generalized weakness and choreoform movements of the tongue and hands. His reflexes were absent and Babinski sign was present bilaterally. A nine-year-old sister was found to have mild ataxia but was otherwise neurologically intact. RESULTS: Molecular genetic studies demonstrated that both siblings were compound heterozygotes with a GAA expansion on one allele and a novel dinucleotide deletion on the other allele. CONCLUSIONS: We describe a novel dinucleotide deletion in the first exon of the FRDA gene in two siblings with FRDA1. Additionally this is the first report of FRDA1 occurring in a family of southeast Asian descent, it demonstrates intrafamilial phenotypic variability, and confirms that atypical phenotypes are associated with compound heterozygosity.     

Friedreich's ataxia with chorea and myoclonus caused by a compound heterozygosity for a novel deletion and the trinucleotide GAA expansion.

Friedreich's ataxia (FRDA) is the most common hereditary ataxia, affecting about 1 in 50,000 individuals. It is caused by mutations in the frataxin gene; 98% of cases have homozygous expansions of a GAA trinucleotide in intron 1 of the frataxin gene. The remaining 2% of patients are compound heterozygotes, who have a GAA repeat expansion in one allele and a point mutation in the other allele. FRDA patients with point mutation have been suggested to have atypical clinical features. We present a case of compound heterozygotes in a FRDA patient who has a deletion of one T in the start codon (ATG) of the frataxin gene and a GAA repeat expansion in the other allele. The patient presented with chorea and subsequently developed FRDA symptoms. The disease in this case is the result of both a failure of initiation of translation and the effect of the expansion. This novel mutation extends the range of point mutations seen in FRDA patients, and also broadens the spectrum of FRDA genotype associated with chorea.     

Mapping of the second Friedreich's ataxia (FRDA2) locus to chromosome 9p23-p11: evidence for further locus heterogeneity

Friedreich's ataxia (FRDA), the most-common form of autosomal recessive ataxia, is inherited in most cases by a large expansion of a GAA triplet repeat in the first intron of the frataxin (X25) gene. Genetic heterogeneity in FRDA has been previously reported in typical FRDA families that do not link to the FRDA locus on chromosome 9q13. We report localization of a second FRDA locus (FRDA2) to chromosome 9p23-9p11, and we provide evidence for further genetic heterogeneity of the disease, in a family with the classic FRDA phenotype.     

Direct evidence that mitochondrial iron accumulation occurs in Friedreich ataxia.

Friedreich ataxia (FRDA) is due to mutations in the FRDA gene (FRDA). When the gene homologous to FRDA is knocked out in yeast, there is accumulation of iron in mitochondria and reduced respiratory function. So far, there is only indirect evidence to support the hypothesis that FRDA is due to accumulation of mitochondrial iron leading to increased production of free radicals. We show here that mitochondrial iron is significantly higher in fibroblasts from patients with FRDA than in control fibroblasts. This is the first direct evidence that the findings in yeast are reproducible in cells from patients with FRDA.     

Friedreich's ataxia: past, present and future

Friedreich's ataxia (FRDA) is an autosomal recessive inherited disorder characterized by progressive gait and limb ataxia, dysarthria, areflexia, loss of vibratory and position sense, and a progressive motor weakness of central origin. Additional features include hypertrophic cardiomyopathy and diabetes. Large GAA repeat expansions in the first intron of the FXN gene are the most common mutation underlying FRDA. Patients show severely reduced levels of a FXN-encoded mitochondrial protein called frataxin. Frataxin deficiency is associated with abnormalities of iron metabolism: decreased iron-sulfur cluster (ISC) biogenesis, accumulation of iron in mitochondria and depletion in the cytosol, enhanced cellular iron uptake. Some models have also shown reduced heme synthesis. Evidence for oxidative stress has been reported. Respiratory chain dysfunction aggravates oxidative stress by increasing leakage of electrons and the formation of superoxide. In vitro studies have demonstrated that Frataxin deficient cells not only generate more free radicals, but also show a reduced capacity to mobilize antioxidant defenses. The search for experimental drugs increasing the amount of frataxin is a very active and timely area of investigation. In cellular and in animal model systems, the replacement of frataxin function seems to alleviate the symptoms or even completely reverse the phenotype. Therefore, drugs increasing the amount of frataxin are attractive candidates for novel therapies. This review will discuss recent findings on FRDA pathogenesis, frataxin function, new treatments, as well as recent animal and cellular models. Controversial aspects are also discussed.     

Atypical Friedreich ataxia in patients with FXN p.R165P point mutation or comorbid hemochromatosis

BackgroundCompound heterozygosity for a trinucleotide repeat expansion and a point mutation in the FXN gene is a rare cause of Friedreich ataxia (FRDA).MethodsWe identified three Swedish FRDA patients with an FXN p.R165P missense mutation and compared their clinical features with six homozygote trinucleotide repeat expansion carriers. Patients were assessed clinically. Trinucleotide expansion length was determined and lymphocyte frataxin levels measured.Resultsp.R165P mutation carriers became wheelchair bound early, but had retained reflexes, better arm function, milder dysarthria, and were more independent in activities of daily living. One p.R165P mutation carrier developed psychosis. Frataxin levels were higher than in homozygous trinucleotide expansion patients. One patient with homozygous trinucleotide repeat expansions and comorbid hemochromatosis had more severe FRDA symptoms than his sibling without hemochromatosis.Conclusionp.R165P patients progress to a less disabling disease state than typical FRDA. Comorbid hemochromatosis may worsen FRDA symptoms through additive effects on iron metabolism.