Prevalence of hereditary hearing impairment in adults.

This contribution, part of an EU-Concerted Action on the genetics of hearing impairment (H.E.A.R.), describes the preliminary estimated prevalence of hereditary hearing impairment based on retrospective data from a clinical series. Of 27,692 subjects examined in the period 1987-91, we sampled 1265 suffering from unilateral or bilateral hereditary hearing impairment, which is roughly 5% of those examined (n = 384 (31%) male; n = 881 (69%) female). Median age of the subjects is 70 years (range 22-98). Subdividing them into 10-year birth cohorts and applying the local annual population statistics, the prevalence of an overall age-related hereditary hearing impairment was roughly estimated to be 3.2/1000, reflecting prevalences as a function of age from 0.8 to 9.4/1000--prevalence in females being significantly more than in males (4.1/1000 and 2.1/1000, respectively). Overall, a moderate hearing impairment of median 51 dB in the better hearing ear was found, averaged across 0.5-4 kHz, this being fairly constant up to the age of 60, when a significant reduction in hearing sensitivity developed. No significant differences are present as a function of gender, except for the birth cohorts 1910-19 and 1920-29. The most frequent type of hereditary hearing impairment in this sample is otosclerosis, comprising 2% of the total clinical series with a rough population prevalence estimate of 1.4/1000. It is concluded that the established database may be of importance in the aggregation of very rare diseases, and for providing the inspiration for future prospective population studies, resulting in knowledge on the epidemiology of hereditary hearing impairment in adults.