Gauging how patients make sense of sound may help track FA severity

Hearing-related brain deficits could help track the disease in patients, lab models

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Measuring abnormalities in the neurological circuits the brain uses to make sense of sound could be a useful way to track the severity of Friedreich’s ataxia in people with the disease as well as in laboratory models, a new study reports.

The study, “Auditory neuropathy in mice and humans with Friedreich ataxia,” was published in the journal Annals of Clinical and Translational Neurology.

Hearing problems are a common symptom of Friedreich’s ataxia. The disease generally doesn’t affect the cells in the ear that are needed to detect sounds — but, it can cause problems with the nerve circuits that the brain normally uses to make sense of the sounds a person is hearing. For example, many people with Friedreich’s ataxia have difficulty carrying on a conversation in settings with a lot of background noise.

Several mouse models of Friedreich’s ataxia have been developed. While prior research has investigated how motor function is affected in mouse models, there hasn’t been any study of how hearing is affected in such models.

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Study set out to measure auditory deficits in mouse model

In the study, scientists in Australia conducted tests to see how hearing is affected in a mouse model of Friedreich’s ataxia, referred to as the YG8Pook/J model.

“An appropriate mouse model could help determine if auditory function is a reliable marker for onset and progression of the disease and provide a model for testing treatments and interventions,” the scientists wrote. “A central aim of this study, therefore, was to investigate whether auditory deficits are present in a mouse model of [Friedreich’s ataxia] and, if so, to quantify changes over time.”

They compared eight YG8Pook/J mice with eight wild-type mice that served as controls. In line with prior results, the YG8Pook/J mice showed notable impairments on tests of balance, suggesting motor problems comparable to what people with the disease experience.

To assess hearing-related brain circuits, the researchers calculated a measure called auditory steady-state response (ASSR). Simplistically, this is measured using specialized probes to record electrical activity in the mice’s brains in response to specific sounds.

Results showed reduced ASSR activity in the YG8Pook/J mice compared to the wild-type mice. Data specifically suggested that mice in both groups experienced a reduction in hearing-related brain activity as they aged, but this was generally more pronounced among the mice with Friedreich’s ataxia.

Statistical analyses showed significant correlations between auditory and motor tests — in other words, mice with more severe hearing-related abnormalities also tended to have more issues with balance. Analyses of brain tissue also indicated that mice with Friedreich’s ataxia-like disease had lower densities of nerve cells in specific brain regions related to hearing.

To corroborate these findings in people, the researchers conducted similar measures of brain electrical activity for 37 volunteers with Friedreich’s ataxia. Results showed that reduced ASSR activity correlated with both reduced speech perception ability and more severe overall Friedreich’s ataxia disease.

Collectively, these data suggest that ASSR, as an objective measure of hearing-related brain abnormalities, could be a useful way to track the severity of disease, both for people with Friedreich’s ataxia and in experimental models of the disease.

“We have shown that ASSR assessment may provide an objective means of tracking the neurodegenerative course in patients with” Friedreich’s ataxia, the researchers concluded.