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Genetic Similarity and Variability among Ashkenazi Jews and Usher Syndrome Type III

Genetic Similarity and Variability among Ashkenazi Jews and Usher Syndrome Type III

Background: Usher syndrome is a genetic disorder that causes deafness and progressive blindness. Usher syndrome accounts for approximately 5% of all cases of deafness, and over one-half of cases of combined deafness and blindness in children. In one type of Usher syndrome (type III), the hearing loss begins after birth and steadily progresses over time. Usher syndrome type III was previously considered very rare, comprising less than 10% of all individuals with Usher syndrome, except in the Finnish population.

Advances: NIDCD intramural scientists have now shown that Usher syndrome type III is present in the Ashkenazi Jewish community, accounting for approximately 40% of all cases of Usher syndrome in this population. Furthermore, all of the Ashkenazi Jewish cases studied were caused by an identical mutation of the USH3 gene, which greatly simplifies molecular diagnosis and carrier screening for this disorder. This study showed that there is great variability in the onset and progression of the loss of vision and hearing associated with this specific mutation raising the possibility that interventions may be developed to prevent or retard these degenerative processes.

Implications: This study demonstrated that Ashkenazi Jewish children with progressive hearing loss should undergo ophthalmologic evaluation, and children with a specific kind of blindness, called retinitis pigmentosa, should have routine audiologic testing to screen for Usher syndrome, type III. In combination with genetic testing for this specific mutation, these evaluations will facilitate the early diagnosis of type III Usher syndrome as well as planning for the difficult communication and rehabilitation challenges presented by these dual deficits.