Dataset Information

Channelopathies Are a Frequent Cause of Genetic Ataxias Associated with Cerebellar Atrophy.

ABSTRACT:

Background

Cerebellar atrophy is a nonspecific imaging finding observed in a number of neurological disorders. Genetic ataxias associated with cerebellar atrophy are a heterogeneous group of conditions, rendering the approach to diagnosis challenging.

Objectives

To define the spectrum of genetic ataxias associated with cerebellar atrophy in a Canadian cohort and the diagnostic yield of exome sequencing for this group of conditions.

Methods

A total of 92 participants from 66 families with cerebellar atrophy were recruited for this multicenter prospective cohort study. Exome sequencing was performed for all participants between 2011 and 2017 as part of 1 of 2 national research programs, Finding of Rare Genetic Disease Genes or Enhanced Care for Rare Genetic Diseases in Canada.

Results

A genetic diagnosis was established in 53% of families (35/66). Pathogenic variants were found in 21 known genes, providing a diagnosis for 31/35 families (89%), and in 4 novel genes, accounting for 4/35 families (11%). Of the families, 31/66 (47%) remained without a genetic diagnosis. The most common diagnoses were channelopathies, which were established in 9/35 families (26%). Additional clinical findings provided useful clues to specific diagnoses.

Conclusions

We report on the high frequency of channelopathies as a cause of genetic ataxias associated with cerebellar atrophy and the utility of exome sequencing for this group of conditions.

SUBMITTER: Gauquelin L

PROVIDER: S-EPMC7604675 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:OBJECTIVES/BACKGROUND: Ataxia with oculomotor apraxia defines a group of genetically distinct recessive ataxias including ataxia-telangectasia (A-T, ATM gene), ataxia with oculomotor apraxia type 1 (AOA1, APTX gene) and type 2 (AOA2, SETX gene). Although, a few unique clinical features differentiate each of these forms, the patients also share common clinical signs, such as the presence of cerebellar atrophy, sensorimotor axonal neuropathy, and elevated alpha-fetoprotein (AFP) serum level. MATERIALS AND METHODS: We selected 22 Italian patients from 21 families, presenting progressive cerebellar ataxia, axonal neuropathy, and elevated serum AFP. We screened the coding regions of ATM, APTX and SETX genes for point mutations by direct sequencing or DHPLC, and searched genomic rearrangements in SETX by MLPA analysis. In selected cases, quantification of ATM and senataxin proteins was performed by Western blot. Clinical, neurophysiological, and neuroimaging data were collected. RESULTS: Thirteen patients (12 families) carried SETX mutations (AOA2, 57%), two were mutated in ATM (A-T), and three in APTX (AOA1). In three remaining patients, we could not find pathogenic mutations, and in one case we found, in homozygosis, the SETX p.K992R polymorphism (population frequency 1-2%). In AOA2 cases, we identified 14 novel and three reported SETX mutations. Signs at onset were gait ataxia and facial dyskinesia, and the age ranged between 11 and 18 years. None had obvious oculomotor apraxia at the latest examination (age 14-45 years). The patient carrying the p.K992R SETX polymorphism had a phenotype similar to that of the diagnosed AOA2 patients, while the other three undiagnosed subjects had a very late onset and a few distinguishing clinical features. DISCUSSION AND CONCLUSIONS: We describe a large series of 13 AOA2 Italian patients. The phenotype was consistent with previous descriptions of AOA2, except for a higher frequency of strabism, and for the absence of oculomotor apraxia. In our survey ~60% of juvenile-to-adult cases with cerebellar ataxia, sensorimotor neuropathy and increased AFP are due to mutations in the SETX gene, and a smaller percentage to APTX and ATM gene mutations.