Expression pattern of Connexin 26 and Connexin 30 in mature cochlea of the monkey

Vestibular Impairment and Postural Development in Children With Bilateral Profound Hearing Loss

Importance

Children with profound hearing loss (HL) and vestibular impairment have worse cochlear implant outcomes compared with those without vestibular impairment. However, the decision for cochlear implantation is rarely based on vestibular function assessment as a complement to audiologic testing.

Objectives

To identify the prevalence of vestibular impairment according to HL origin and to assess the association between vestibular impairment and delayed posturomotor development in children with profound HL.

Design, Setting, and Participants

This cohort study was conducted in a pediatric referral center for cochlear implantation in Paris, France, using medical records data on HL origin, vestibular assessment, and ages of developmental milestone achievement. The cohort included children with profound HL (loss >90 dB HL) who completed vestibular assessment prior to cochlear implantation between January 1, 2009, and December 31, 2019. Data analyses were conducted between January and June 2023.

Main Outcomes and Measures

The primary outcome was prevalence of vestibular impairment according to HL origin. Children were classified into 3 groups according to their responses to vestibular testing: normal vestibular function (NVF), partially impaired vestibular function (PVF), and complete bilateral vestibular loss (CBVL). Generalized logit models were performed to evaluate the association between vestibular impairment and causes of HL as well as posturomotor development delay.

Results

A total of 592 children were included (308 males [52.0%]; mean [SD] age, 38 [34] months). In children with documented HL origin (n = 266), 45.1% (120) had HL with genetic origin, 50.0% of which were syndromic (mainly Usher and Waardenburg syndromes) and 50.0% were nonsyndromic (mainly associated with connexin 26). Among patients with infectious HL origin (n = 74), 70.3% (52) had cytomegalovirus (CMV) infection. Vestibular impairment was found in 44.4% (263 of 592) of the children; it was mostly symmetrical in 88.9% (526) and was CBVL in 5.7% (34) of the cases. Vestibular impairment was present in 78.3% (47) of children with genetic syndromic HL (56.7% [34] with PVF; 21.7% [13] with CBVL) and in 69.2% (36) of children with CMV infection (57.7% [30] with PVF; 11.5% [6] with CBVL). Genetic syndromic HL origin was found to be more often associated with both PVF and CBVL than other HL causes. The odds of having delays in 4 developmental milestones (head holding, sitting, standing with support, and independent walking) were higher in both PVF and CBVL (eg, head-holding odds ratios: 2.55 and 4.79) compared with NVF, and the age of achieving these milestones was higher in CBVL than PVF (eg, head holding: 7.33 vs 4.03 years; P < .001). All 4 developmental milestones were associated with the degree of vestibular impairment.

Conclusions and Relevance

This cohort study found that among children with profound HL, vestibular impairment was prevalent, varied according to HL origin, and associated with posturomotor development; while all developmental milestones were associated with vestibular impairment severity, not all HL causes were associated with vestibular impairment severity. Children with profound HL may benefit from complete vestibular assessment before cochlear implantation, which would support early and adapted management, such as physical therapy for CBVL and cochlear implantation strategy.

Purification of Fibroblasts From the Spiral Ganglion

Using cultures of freshly isolated spiral ganglion cells (SGC) is common to investigate the effect of substances on spiral ganglion neurons (SGN) in vitro. As these cultures contain more cell types than just neurons, and it might be beneficial to have cochlear fibroblasts available to further investigate approaches to reduce the growth of fibrous tissue around the electrode array after cochlear implantation, we aimed at the purification of fibroblasts from the spiral ganglion in the current study. Subcultivation of the primary SGC culture removed the neurons from the culture and increased the fibroblast to glial cell ratio in the preparations, which was revealed by staining for vimentin, the S100B-protein, and the 200-kD neurofilament. We performed direct immunolabeling for the Thy1-glycoprotein and the p75NGFR-enabled fluorescence-based cell sorting. This procedure resulted in a cell culture of cochlear fibroblasts with a purity of more than 99%. The received fibroblasts can be subcultivated for up to 10 passages before proliferation rates drop. Additionally, 80% of the cells survived the first attempt of cryopreservation and exhibited a fibroblast-specific morphology. Using the described approach provides a purified preparation of cochlear fibroblasts, which can now be used in vitro for further investigations.

Gene therapy for genetic mutations affecting non-sensory cells in the cochlea

Congenital hearing loss (HL) affects about 1 in every 500 infants. Among those affected more than half are caused by genetic mutations. According to the cellular sites affected by mutations in the cochlea, deafness genes could be classified into three major groups: those affecting the function of hair cells and synapses, cochlear supporting cells, and cells in the stria vascularis (SV) as well as in the lateral wall. The second and third groups account for more than half of all sensorineural hearing loss (SNHL) cases caused by genetic mutations. Current major treatment options for SNHL patients are hearing aids and cochlear implants (CIs). Hearing aids can only help patients with moderate to severe HL. Resolution of CIs is still improving and these devices are quite expensive especially when lifetime rehabilitation and maintenance costs are included. Tremendous efforts have been made to find novel treatments that are expected to restore hearing with higher-resolution and more natural quality, and to have a significantly lower cost over the lifetime of uses. Gene therapy studies have made impressive progresses in preclinical trials. This review focuses on deafness genes that affect supporting cells and cells in the SV of the cochlea. We will discuss recent progresses and remaining challenges for gene therapies targeting mutations in deafness genes belonging to this category.