ABSTRACT
An extended Dutch family with hereditary hearing impairment was first described in 1966 (1, 2) and ever since followed up clinically (3-6). The hearing loss follows an autosomal dominant inheritance pattern with complete penetrance in more than 100 affected individuals (Fig. 1). No additional symptoms are present, indicating that the hearing loss is nonsyndromic. The hearing loss is bilateral, affecting both ears equally. None of the patients ever reported tinnitus or vertigo (1, 2). The hearing impairment is sensori-neural, and starts between 5 and 15 years of age in the high frequencies, with a progressive loss following a characteristic pattern. First the high-tone losses increase to approximately 80 dB, but low-frequency thresholds remain normal (Fig. 2A). Only when the high-tone thresholds further deteriorate beyond 80 dB do the lower frequencies become affected as well (Fig. 2B). A mean high-frequency loss of approximately 7 dB/year was calculated, but the progression rate significantly differs between individual patients. Fast-progressing patients exhibit their first symptoms at age 5, the lower frequencies become affected by age 15, and the endstage is reached by age 20-25. On the other hand, slowly progressing patients have their first complaints before age 15, low frequencies become affected before age 40 and the endstage is reached in the sixth decade (5, 6). When the endstage is established, audiograms show profound hearing impairment at the higher frequencies and severe hearing impairment at the lower frequencies (Fig.
