A novel locus for Usher syndrome type II, USH2B, maps to chromosome 3 at p23-24.2

Usher type II syndrome is defined by the association of retinitis pigmentos a, appearing in the late second to early third decade of life,,vith congeni tal moderate to severe non-progressive hearing loss, This double sensory im pairment is not accompanied by vestibular dysfunction, To date, only one Us her type II locus, USH2A, at chromosome band 1q41, has been defined. Here, we demonstrate by linkage analysis, that the gene responsible for Usher typ e II syndrome in a Tunisian consanguineous family maps to chromosome 3 at p osition p23-24.2, thus providing definitive evidence for the genetic hetero geneity of the syndrome. A maximum lod score of 4.3 was obtained with the p olymorphic microsatellite markers corresponding to loci D3S1578, D3S3647 an d D3S3658, This maps the gene underlying USH2B to a chromosomal region whic h overlaps the interval defined for the non-syndromic sensorineural recessi ve deafness DFNB6, raising the possibility that a single gene underlies bot h defects, However, the audiometric features in the patients affected by US H2B and DFNB6 are very different.