GENE-MAPPING OF USHER SYNDROME TYPE IIA - LOCALIZATION OF THE GENE TOA 2.1-CM SEGMENT ON CHROMOSOME 1Q41

Usher syndrome type II is associated with hearing loss and retinitis p igmentosa but not with any vestibular problems. It is known to be gene tically heterogeneous, and one locus (termed USH2A) has been linked to chromosome 1q41. In an effort to refine the localization of USH2A, th e genetic map of the region between and adjacent to the marker loci pr eviously recognized as flanking USH2A (D1S70 and PPOL) is updated. Ana lysis of marker data on 68 Usher II families places the USH2A gene int o a 2.1-cM region between the markers D1S237 and D1S229. The gene for transforming growth factor beta 2 (TGFB2) and the gene for the homeodo main box (HLX1) are both eliminated as candidates for USH2A, by virtue of their localization outside these flanking markers. The earlier fin ding of genetic heterogeneity was confirmed in six new families, and t he proportion of unlinked Usher II families is estimated at 12.5%. The placement of the USH2A gene into this region will aid in the physical mapping and isolation of the gene itself.