The Usher syndrome type 2A: clinical findings in obligate carriers.

Ten obligate carriers of Usher syndrome type 2A from 5 different families with 2 affected persons all underwent audiologic, vestibular and ophthalmologic examinations. They had a sensorineural hearing loss which was in excess of that expected for their age at all of the frequencies (0.25-8 kHz) tested, however, only a 10 dB (average) excess in hearing loss at 0.25-0.5 kHz proved to be significant. The speech discrimination scores obtained conformed with the hearing thresholds. Tympanometry, acoustic reflex and brain stem auditory-evoked potential findings were generally normal. Some vestibular abnormalities were found in a minority of the carrier sample, but not beyond the level of false positivity. Ophthalmologic findings were essentially normal, although in 5 carriers there was a subnormal electrooculography (EOG). These findings are not sufficient specific for carrier detection.