Age-related hearing impairment (ARHI): environmental risk factors and genetic prospects.

This paper reviews what is known about the environmental risk factors and medical conditions that contribute to age-related hearing impairment (ARHI), and evaluates which analyses could be performed to identify genetic factors that are involved. Although hearing acuity declines with aging in everybody, the variation in hearing thresholds is large. Part of this variation can be explained by medical conditions, and by a different exposure to environmental factors. In particular, many studies have been dedicated to the influence of occupational noise on hearing. The importance of other environmental risk factors is less clear and often controversial. In contrast, almost nothing is known about the genetic compound of ARHI. Heritability estimates have shown that approximately half of the variance in ARHI is due to heritable factors, which indicates that ARHI is a complex trait, influenced by an interplay between genetics and environment. Although several genes for monogenic hearing impairment have been identified in mouse and man, no susceptibility genes for ARHI have been identified yet. The methodology to dissect the genetics of complex traits is still developing. Possible study designs to unravel the genetics of ARHI are discussed.