The changing face of Usher syndrome: clinical implications.

Usher syndrome is both genetically and phenotypically heterogeneous. Traditionally, the condition has been classified into three clinical types, differentiated by the severity and progression of the hearing impairment and by the presence or absence of vestibular symptoms. Recent advances in molecular genetics have enabled researchers to study the phenotypic expression in confirmed molecular groups of Usher. In response to the expansion of clinical and genetic information on Usher, we report an up to date review of the different clinical forms of Usher in known molecular groups and use the emerging evidence to appraise the diagnostic utility of the traditional classification of Usher. Our findings undermine the traditional view that the clinical types of Usher have distinct genetic causes. The pleiotropic effects of some of the major causes of Usher lead to considerable overlap between the different clinical types, with very little evidence for phenotypic-genotypic correlations. The novel synthesis emerging from this review suggests more productive approaches to the diagnosis of Usher in hearing-impaired children which would provide more accurate prognostic information to families.