Hearing impairment in the adult population (presbycusis) is estimated to affect 45.9 % of individuals over age 48. Although environmental exposures play a role in age related hearing impairment, studies in both human populations and animal models indicate that there is a strong genetic predisposition to presbycusis. In our study, we will follow-up results of a genome wide scan in 328 extended pedigrees in Framingham Heart Study, a large, community-based longitudinal study. In this cohort, hearing was measured as a pure tone thresholds averaged (PTA) across distinct frequencies (low, medium and high). We found sensory presbycusis, predominantly high frequency loss, to be the most common form of hearing loss. Strial presbycusis, a relatively flat loss across the low-frequency spectrum with variable degrees of high-frequency loss, was less common than sensory but it showed the greater heritability estimates. From linkage analysis, at least 6 locations were identified that warrant further investigation. It is our plan to identify the specific genetic factors that contribute to the development of presbycusis at these chromosomal locations. To accomplish this, we will type additional microsatellite and SNP markers to refine the location of the gene. We will then broaden our search for genes important for hearing by typing SNP markers in a large number of cochlear genes and other genes important for hearing. We expect that this will assist us in identifying genes not detected by the genome scan. It is our expectation that this work will contribute to understanding the role of specific genes, genetic variations and the interaction between genes and environment in presbycusis. It will also provide avenues of research that may lead to new therapies that will reduce or eliminate age onset hearing loss.
Clinton T. Baldwin, Ph.D.