Carriers of the Usher syndrome type IB: is audiometric identification possible?

Some studies in the past have shown that carriers of genes for recessive deafness cannot be identified by standard audiometry. However, remarkable results with regard to the identification of heterozygotes have been reported using Békésy audiometry and Audioscan audiometry. In the present study, nine obligate carriers from five families with the Usher syndrome type IB were examined. Methods that reflect the function of the cochlea, including pure-tone audiometry, Audioscan audiometry, and otoacoustic emission measurements were used to detect (subtle) audiometric manifestations of heterozygosity. Abnormalities in hearing sensitivity were found in some obligate carriers but to the same extent in some of the controls. No statistically significant differences were found in the presence of audiometric abnormalities between carriers and controls. Additional audiologic measurements indicated that if hearing loss was present in Usher type IB carriers, it was presumably of cochlear origin. It is concluded that carriers of the Usher syndrome type IB cannot be identified properly via standard audiometric methods.