Clarin-2 gene supplementation durably preserves hearing in a model of progressive hearing loss.

Hearing loss is a major health concern affecting millions of people worldwide with currently limited treatment options. In clarin-2-deficient Clrn2-/- mice, used here as a model of progressive hearing loss, we report synaptic auditory abnormalities in addition to the previously demonstrated defects of hair bundle structure and mechanoelectrical transduction. We sought an in-depth evaluation of viral-mediated gene delivery as a therapy for these hearing-impaired mice. Supplementation with either the murine Clrn2 or human CLRN2 genes preserved normal hearing in treated Clrn2-/- mice. Conversely, mutated forms of CLRN2, identified in patients with post-lingual moderate to severe hearing loss, failed to prevent hearing loss. The ectopic expression of clarin-2 successfully prevented the loss of stereocilia, maintained normal mechanoelectrical transduction, preserved inner hair cell synaptic function, and ensured near-normal hearing thresholds over time. Maximal hearing preservation was observed when Clrn2 was delivered prior to the loss of transducing stereocilia. Our findings demonstrate that gene therapy is effective for the treatment of post-lingual hearing impairment and age-related deafness associated with CLRN2 patient mutations.

Tinnitus distress: a paradoxical attention to the sound?

Tinnitus, the perception of sound in the absence of external stimuli, is often a disturbing symptom for which the underlying functional neuroanatomy still remains poorly understood. Most studies have focused solely on functional connectivity changes in the auditory cortex of tinnitus patients. The aim of this study was to investigate whether a correlation exists between tinnitus behavioural scores and functional brain connectivity of five resting-state networks comprising the auditory, the default mode, the external control left and right, and the salience network. For this purpose, a large sample of one hundred and thirty-five subjects underwent resting-state functional magnetic resonance imaging and their behavioural scores were obtained using clinical evaluations. Networks were extracted using independent component analysis, and functional connectivity patterns in the extracted networks were evaluated by a graph theoretical approach. The effects of tinnitus for each network were investigated by correlating the graph strength of all the regions with the tinnitus behavioural scores using stepwise fit regression analysis. Results indicated that alterations of functional interactions between key neural circuits of the brain are not limited to one single network. In particular, tinnitus distress showed a strong correlation with the connectivity pattern within and between the right executive control network and the other four resting-state networks, indicating that tinnitus distress is probably the consequence of a hyperactive attention condition. Among the behavioural scores, the strongest correlation was observed between age and hearing loss, while the tinnitus objective loudness was not correlated with any behavioural scores.