Age-related hearing impairment (ARHI;also called presbycusis) impairs sensory input in more than a half of a billion people [1, 2], and the WHO predicts that the impact on public health will only increase as the median age of the population steadily increases (www.who.int/en/). A number of studies indicate that AHRI negatively impacts quality of life [2-5]. A cross-sectional survey of 131,535 Canadians reported that subjects with hearing impairment suffer higher rates of depression [6], while a study of 1140 elderly, linked hearing deficits with a significant increase in mortality risk in men [7]. The age of onset for ARHI varies markedly;with overall prevalence increasing steadily with age, so that 60% of individuals aged 70 to 80 demonstrate significant hearing impairment [8, 9]. Our team has recently completed the first genome-wide association study (GWAS) identifying several susceptibility alleles for ARHI [10] A major strength of this proposal lies in the group of investigators we have assembled. Each of the centers brings unique strengths and capabilities. The investigators from the House Ear Institute and the University of Antwerp have expertise in the genetics of hearing loss, GWAS and surgical access to cochlear tissue. Translational Genomics (TGen) has world-renowned expertise in genotyping and copy number variant (CNV) analysis. The success of this team is best illustrated by our discovery and publication of GRM7, the first susceptibility variant for ARHI found in a GWAS [10]. Leveraging these strengths uniquely positions us to dramatically advance our understanding of the underlying genetic architecture that predisposes humans to ARHI. Our LONG-TERM GOAL is to develop a comprehensive understanding of the specific genetic factors that contribute to ARHI. As an initial step towards that objective, we will build methodically upon results from our GWAS by analyzing a comprehensive human adult cochlear transcriptome that has been collected and sequenced by next generation sequencing (NGS). This cochlear transcriptome, and the existing transcriptome data in the mouse, will provide us with the opportunity to up weight genomic regions of association in our GWAS that contain genes expressed in the cochlea. This approach will enhance the power of our study providing a more cost-effective design. We propose the following SPECIFIC AIMS:
AIM 1 : Compile an accurate representation of the adult human cochlear transcriptome. Hypothesis: Genetic variants associated with ARHI reside within genes that are normally expressed in the cochlea. An in-depth characterization of the cochlear transcriptome has been initiated. The molecular biology has been completed and we are beginning the bioinformatics analysis. Several analytical methods exist that allow for weighting of individual SNPs due to biological criteria. We will use the new and existing cochlear gene list to a priori assign specific SNPs additional weight in the analysis of our Aim 2 data.
AIM 2 : Elucidate novel genes and biochemical networks associated with ARHI using a GWAS design. Hypothesis: ARHI is a complex disease resulting from allelic variation in multiple genes. We have recently confirmed the role of genetic variants in ARHI in a GWAS based on a pooling approach that demonstrated allelic association in several genes, including GRM7. Properly powered studies using hypothesis independent models of gene discovery have demonstrated great utility in identifying genomic variation associated with complex diseases. A stepwise approach, with up weighting of genomic regions containing genes expressed in the cochlea, and accounting for known covariant, further increases the power of our study, resulting in a cost-effective design. Our proposed investigation will not only improve our understanding of the genetic bases of ARHI, but will provide a rationale to pursue hypothesis-driven investigations that will in turn advance our understanding of the genetic, molecular, and cellular causes of ARHI. This improved knowledge base can be anticipated to constitute fertile ground for developing new evidence-based preventive and therapeutic approaches to treating ARHI.
Little is known regarding specific genetic determinants of AHRI. We propose studies that will identify such genetic determinants using genetic approaches such as GWA studies that are established in our laboratory and/or that of our collaborators. We propose that this paradigm-wherein genetic studies inform mechanistic studies-may well prove to be a powerful impetus to progress in understanding, preventing, and treating ARHI.
| Schrauwen, Isabelle; Hasin-Brumshtein, Yehudit; Corneveaux, Jason J et al. (2016) A comprehensive catalogue of the coding and non-coding transcripts of the human inner ear. Hear Res 333:266-274 |
| Fransen, Erik; Bonneux, Sarah; Corneveaux, Jason J et al. (2015) Genome-wide association analysis demonstrates the highly polygenic character of age-related hearing impairment. Eur J Hum Genet 23:110-5 |
| Newman, Dina L; Fisher, Laurel M; Ohmen, Jeffrey et al. (2012) GRM7 variants associated with age-related hearing loss based on auditory perception. Hear Res 294:125-32 |
| White, Cory H; Ohmen, Jeffrey D; Sheth, Sonal et al. (2009) Genome-wide screening for genetic loci associated with noise-induced hearing loss. Mamm Genome 20:207-13 |
| Friedman, Rick A; Van Laer, Lut; Huentelman, Matthew J et al. (2009) GRM7 variants confer susceptibility to age-related hearing impairment. Hum Mol Genet 18:785-96 |
