CLINICAL FINDINGS IN OBLIGATE CARRIERS OF TYPE-I USHER SYNDROME

Seventeen obligate carriers from nine families with autosomal recessiv e Usher syndrome type I underwent otological, audiological, vestibular , and ophthalmological examination in order to identify possible manif estations of heterozygosity. Linkage studies were performed and six fa milies showed linkage to chromosome region 11q13.5 while 3 families ha ve so far failed to show Linkage to the candidate regions, Eight oblig ate carriers had an abnormal puretone audiogram, Two different audiome tric patterns could be distinguished when hearing loss was corrected f or age and sex, Four carriers (24%) had significant sensorineural hear ing loss (SNHL) which increased at higher frequencies. The other 13 ca rriers had SNHL of about 10 dB at 0.25 and 0.5 kHz, but less at higher frequencies, Vestibular findings were generally normal. Electrooculog raphy demonstrated a significant lower mean light peak/dark trough rat io in Usher type I carriers compared to normal control individuals. Th e methods used in this study were found not to be specific enough to c linically identify carriers of Usher type I syndrome. Nevertheless it is remarkable that a number of obligate carriers showed significant au diological and ophthalmological abnormalities. (C) 1995 Wiley-Liss, In c.