Hearing loss and tinnitus: genetic and environmental effects

Depending on the criteria used 1/3 - 1/6 of the population experience hearing impairment. Tinnitus is defined as the sensation of sound without any outer sound stimulus present. Environmental risk factors such as noise exposure are frequently described fo r both the diseases. A genetic component of hearing loss has been reported in a limited number of studies. Knowledge of causes of tinnitus is scarce and studies of the heritability of tinnitus have not been published. The importance of interaction between genetic and environmental risk factors has never previously been reported. The aims of this study are to: 1.Estimate the heritability of hearing loss in the younger part of the population 2.Eestimate the heritability of age related hearing loss 3.Quant ify the importance of genetic and environmental factors common to hearing loss at high, middle and low frequencies and the importance of genes and environment specific to hearing threshold at each frequency 4.Estimate the heritability of tinnitus 5.Explo re to what extent the association between tinnitus and hearing loss can be explained by common genetic or environmental risk factors Data from the Nord-Trøndelag hearing loss study, containing questionnaire data and audiometric tests on 50138 persons, wil l be used. The data are matched with person-records from Statistics Norway, including familial relationship between the participants. The statistical framework of structural equation modelling will be applied to disentangle the relative contribution from genetic and environmental effects along with gene-environment interaction in these traits. This data set is unique even in an international context and no other survey of this format suitable for genetic epidemiology exists. Knowledge on the causes of hea ring loss and tinnitus is of great importance to improve strategies to prevent the disability associated with these diseases. Such knowledge could improve quality of life for a large number of individuals.