RNA-seq analysis highlights DNA replication and DNA repair associated with early-onset hearing loss in the cochlea of DBA/2J mice

AIMS

Age-related hearing loss (ARHL) is a significant health concern, and DBA/2J (D2) and C57BL/6 (B6) mouse strains serve as valuable models for its study. B6 mice, harboring a homozygous ahl allele in Cdh23, manifest high-frequency hearing loss at 3 months. In contrast, D2 mice, carrying the R109H variant of the Fascin-2 gene (Fscn2), experience early-onset hearing loss by 3 weeks. Yet, the underlying molecular mechanisms driving early-onset hearing loss in D2 mice remain elusive. This study aimed to identify novel genes and regulatory pathways as therapeutic targets for early deafness.

MAIN METHODS

This study employs RNA-sequencing (RNA-seq) to analyze cochlear mRNA expression at two different ages in D2 and B6 mice, respectively. The differentially expressed genes (DEGs) are uniquely associated with D2 mice by Venn diagram analysis. A protein-protein interaction (PPI) network is further constructed, followed by module analysis utilizing MCODE. Enrichment analysis of GO and KEGG pathways revealed biological functions and molecular pathways. The PPI network and VarElect analysis are conducted for genes within these pathways, facilitating the identification of pivotal genes based on scoring criteria. Subsequently, five genes are meticulously selected and validated through qRT-PCR.

KEY FINDINGS

Notably, 1181 DEGs are uniquely associated with D2 mice by Venn diagram analysis. GO and KEGG pathway enrichment analyses shed light on distinctive pathways in D2 mice, encompassing DNA replication, mismatch repair, base excision repair, and nucleotide excision repair, which are associated with apoptosis. Five genes involved in these pathways were finally selected and validated by qRT-PCR. Their down-regulation with age is consistent with RNA-seq result.

SIGNIFICANCE

Our study underscores the potential implication of down-regulated genes associated with DNA replication and DNA damage repair in the early-onset hearing loss observed in D2 mice.

Effects of longstanding degraded auditory signal on visuospatial, visuomotor, and visual attention skills in adults with hearing loss

OBJECTIVE

This study examined the consequences of long-term auditory deprivation on visuospatial functions, visuomotor functions, and visual attention skills in adults with early-onset hearing loss.

METHODS

Fifteen adults with bilateral, early-onset (before age 3), severe-to-profound hearing loss who used spoken language participated in this study. Visuospatial (figure ground, form constancy, visual perception) and visuomotor functions (visuomotor integration, visual search) were examined using norm-referenced tests. Visual attention scales were examined using a computerized program, IVA plus continuous performance test.

RESULTS

As a group, participants performed in the average range on visuospatial and visuomotor functions when compared to normative data presented in the test instruments. However, participants demonstrated below average performance on sustained visual attention. Duration of cochlear implant use positively correlated with one of the visual attention scales, namely visual speed.

CONCLUSIONS

The findings of the current study suggest that adults with early-onset hearing loss may demonstrate difficulties in sustaining attention to visual information. Data also suggest that increased experience with cochlear implant may ameliorate deficits associated with visual attention. Future studies should explore challenges experienced by adults with early-onset hearing loss in their daily activities that may result from this deficit and intervention programs that may enhance visual attention skills.

Exploring reasons for late identification of children with early-onset hearing loss

INTRODUCTION

Several studies have shown that early identification of childhood hearing loss leads to better language outcomes. However, delays in the confirmation of hearing loss persist even in the presence of well-established universal newborn hearing screening programs (UNHS). The objective of this population-based study was to document the proportion of children who experienced delayed confirmation of congenital and early onset hearing loss in a UNHS program in one region of Canada. The study also sought to determine the reasons for delayed confirmation of hearing loss in children.

METHODS

Population level data related to age of first assessment, age of identification and clinical characteristics were collected prospectively for all children identified through the UNHS program. We documented the number of children who experienced delay (defined as more than 3 months) from initial audiologic assessment to confirmation of hearing loss. A detailed chart review was subsequently performed to examine the reasons for delay to confirmation.

RESULTS

Of 418 children identified from 2003 to 2013, 182 (43.5%) presented with congenital or early onset hearing loss, of whom 30 (16.5%) experienced more than 3 months delay from initial audiologic assessment to confirmation of their hearing disorder. The median age of first assessment and confirmation of hearing loss for these 30 children was 3.7 months (IQR: 2.0, 7.6) and 13.8 months (IQR: 9.7, 26.1) respectively. Close examination of the factors related to delay to confirmation revealed that for the overwhelming majority of children, a constellation of factors contributed to late diagnosis. Several children (n = 22; 73.3%) presented with developmental/medical issues, 15 of whom also had middle ear dysfunction at assessment, and 9 of whom had documented family follow-up concerns. For the remaining eight children, additional reasons included ongoing middle ear dysfunction for five children, complicated by family follow-up concerns (n = 3) and mild hearing loss (n = 1) and the remaining three children had isolated reasons related to family follow-up (n = 1) or mild hearing loss (n = 2).

CONCLUSION

Despite the progress made in the early detection of pediatric hearing loss since UNHS, a substantial number of children referred for early assessment can experience late confirmation and intervention. In particular, infants with developmental and/or medical issues including middle ear disorders are at particular risk for longer time to confirmation of hearing loss.