Usher syndrome type III (USH3) is characterized by progressive hearing loss and variable onset and severity of vision problems due to retinitis pigmentosa. Balance is not usually affected. USH3 is inherited in an autosomal recessive manner, and it occurs at increased frequency in the Ashkenazi Jewish population. Mutations in the CLRN1 gene have been demonstrated to contribute to USH3. CLRN1 encodes clarin-1, a transmembrane glycoprotein that is expressed in the retina, olfactory epithelium, hair cells of the Corti, and spinal ganglion cells. It is an autosomal recessive disorder. It occurs more frequently in the Ashkenazi Jewish population, where the carrier rate is 1 in 120.  Ashkenazi Jewish individuals with a negative family history who test negative for the c.459del3 (delATT), p.N48K and p.L150P mutations in CLRN1 have a revised carrier risk of 1 in 5,950.