Late-onset Friedreich's Ataxia Research Articles

Hereditary Ataxias

Hereditary Ataxias

The Yeast Connection to Friedreich Ataxia

We thank John Ashkenas for his editorial assistance and David Koeller for data prior to publication. A.D. and D.P. are supported by grants DK53953-01 and GM57067-01, respectively, from the National Institutes of Health.

Very late onset Friedreich's ataxia without cardiomyopathy is associated with limited GAA expansion in the X25 gene.

Molecular analysis of spinocerebellar ataxias revealed a pathologic GAA expansion in the gene encoding frataxin in six adult patients from three families. These patients, carrying expanded alleles in the low-range size, had an exceptionally late onset and lacked cardiomyopathy, pointing to phenotypic variability of Friedreich's ataxia. Both mitotic and gametic instability of the expanded triplet repeat were present in these families.

Genetics of Friedreich Ataxia

Genotype-phenotype correlations in a group of 100 patients with typical Friedreich ataxia (FRDA), and in three smaller clinically atypical groups (Arcadian FRDA, late-onset FRDA (LOFA), and FRDA with retained reflexes (FARR)), were studied at the Centre de Recherche Louis-Charles Simard, Service de Genetique Medicale, Service de Neurologie, Hopital Sainte-Justine, Departments of Genetics and Medicine, McGill University, Montreal General Hospital, and other centers.

Phenotypic variability in Friedreich ataxia: role of the associated GAA triplet repeat expansion.

We studied genotype-phenotype correlations in a group of 100 patients with typical Friedreich ataxia (FRDA), and in three groups of patients with atypical clinical presentations, including 44 Acadian FRDA, 8 late-onset FRDA (LOFA), and 6 FRDA with retained reflexes (FARR). All patients, except 3 with typical FRDA, carried two copies of the FRDA-associated GAA triplet repeat expansion. Overall, the phenotypic spectrum of FRDA appeared to be wider than defined by the currently used diagnostic criteria. Our study indicated the existence of several sources of variability in FRDA. Patients with larger GAA expansions tended to have earlier onset and were more likely to show additional manifestations of the disease. Mitotic instability of the expanded GAA repeats may partially account for the limited degree of correlation between expansion sizes as determined in lymphocytes and clinical parameters. Some clinical variants associated with specific FRDA haplotypes, such as Acadian FRDA and FARR, turned out to be unrelated to expansion sizes. No polymorphism in the frataxin coding sequence could be associated with these clinical variants.

Late-onset Friedreich's ataxia. Molecular genetics, clinical neurophysiology, and magnetic resonance imaging.

OBJECTIVE--To clarify the nosological classification of late-onset Friedreich's ataxia (LOFA), ie, patients who have later onset of Friedreich's ataxia (FRDA), often after 25 years of age. DESIGN--Comparison of clinical examination data, nerve conduction studies, electronystagmographic recording, and magnetic resonance imaging of a family with LOFA with a group of patients with FRDA. Genetic linkage analysis was performed in the family with LOFA. SETTING--Referral center. PATIENTS--Thirteen patients satisfied classic diagnostic criteria of FRDA, and three patients from one family satisfied all diagnostic criteria of FRDA but with disease onset after 25 years. RESULTS--Results of nerve conduction studies, electronystagmographic recording, and magnetic resonance imaging in patients with LOFA closely corresponded to observations made in patients with FRDA. In addition, genetic linkage analysis using markers tightly linked to the FRDA locus on chromosome 9 showed that all affected members of the LOFA family, but not their unaffected siblings, had inherited identical paternal and maternal genotypes. CONCLUSIONS--Data suggest that LOFA may also result from mutation within the FRDA locus.

Magnetic resonance imaging in hereditary and idiopathic ataxia.

We used magnetic resonance imaging (MRI) to study brain and spinal cord morphology in hereditary and idiopathic ataxia. Our interest was in whether the classical neuropathologic categories--cerebellar cortical atrophy (CCA), olivopontocerebellar atrophy (OPCA), and spinal atrophy (SA)--could be identified in vivo and which clinical phenotype corresponded to which morphologic category. To this end, we measured the size of the cerebellar vermis, cerebellar hemispheres, fourth ventricle, middle cerebellar peduncles, basis pontis, medulla oblongata, and cervical spinal cord on T1-weighted images of 61 patients and 24 healthy controls. Five patients with Friedreich's ataxia (n = 7) and all with late-onset Friedreich's ataxia (n = 3) had SA without major involvement of the brainstem or cerebellum. Morphologic findings in patients with early-onset cerebellar ataxia with retained tendon reflexes (n = 11) were heterogeneous: six patients had MRI findings compatible with CCA, and two patients had a combination of SA and CCA. The three remaining patients had an atypical pattern of atrophy. Similarly, the morphologic changes in patients with autosomal-dominant cerebellar ataxia with additional noncerebellar symptoms (ADCA-I; n = 13) were nonuniform: atrophic changes typical for CCA, OPCA, or SA were each present in one case, four patients had a combination of OPCA and SA, and the remaining patients could not be assigned to one of the morphologic categories. In autosomal-dominant cerebellar ataxia with a pure cerebellar syndrome (ADCA-III; n = 6), all patients except one had CCA.(ABSTRACT TRUNCATED AT 250 WORDS)

A controlled retrospective follow-up study of the impact of genetic counselling on parental reproduction following the birth of a Down syndrome child: Oetting, L.A. and Steele, M.W. Childrens Hosp., Pittsburgh, PA, U.S.A. Clin. Genet. 21(1), 7–13, 1982

This chapter discusses the clinical features and pathology of Friedreich ataxia (FA) that is the most common of the early-onset hereditary ataxias in Caucasians. The identification of the FA gene (FRDA) and its most common mutation, the unstable hyperexpansion of a GAA triplet repeat sequence (TRS) allowed to better define the clinical and pathologic spectrum of the disease. Studies suggest that the disease shows a remarkable clinical variability, sometimes even within the same sibship that is a rather uncommon finding for recessive disorders. Variability involves age at onset, rate of progression, and overall severity. Cardiomyopathy, kyphoscoliosis, pes cavus, optic atrophy, hearing loss, and diabetes mellitus occur only in some patients. Atypical cases with an overall FA-like phenotype but missing some of the essential diagnostic features can be identified. These include late-onset FA (LOFA) that develops after the age of 25 years, sometimes as late as the sixth decade, and FA with retained tendon reflexes (FARR). The FRDA locus is in the proximal long arm of chromosome 9. The gene contains seven exons spanning 95 kb of genomic DNA. The major, and probably only, functionally relevant messenger RNA (mRNA) has a size of 1.3 kb, corresponding to the first five exons, numbered 1–5a.