Abstract
The Usher syndrome (USH) is a group of recessively inherited disorders characterized by deafness and vision loss. The standard Usher syndrome classification recognizes three clinical types. Usher syndrome type 1 (USH1) is the most severe form of USH. It appears to have profound non-syndromic hearing loss and vestibular dysfunction in childhood and retinitis pigmentosa develops in later years. Five causative genes have been identified: MYO7A, USH1C, CDH23, PCDH15, and USH1G. We previously reported that the basis for the classification of USH is ambiguous. It was particularly unclear whether the diagnosis regarding the vestibular dysfunction of USH1 was based on a vestibular examination or a complaint of dizziness. In this study, we considered cases in which USH1 gene mutations were identified. Of five USH1 patients, only two patients (50%) complained of dizziness. However, all patients had no response to the caloric test. In addition, two patients demonstrated delayed onset of walking (18 months and 24 months). In conclusion, we think the assessment of USH1 vestibular function should be based on a vestibular examination. Moreover, a delay in motor development is one clinical indication of the congenital absence of vestibular function.
