Homozygosity mapping to the USH2A locus in two isolated populations

Usher syndrome is a group of autosomal recessive disorders characterised by progressive visual loss from retinitis pigmentosa and moderate to severe s ensorineural hearing loss. Usher syndrome is estimated to account for 6-10% of all congenital sensorineural hearing loss. A gene locus in Usher type I I (USH2) families has been assigned to a small region on chromosome 1q41 ca lled the UHS2A locus. We have investigated two families with Usher syndrome from different isolated populations. One family is a Norwegian Saami famil y and the second family is from the Cayman Islands. They both come from rel atively isolated populations and are inbred families suitable for Linkage a nalysis. A lod score of 3.09 and 7.65 at zero recombination was reached res pectively in the two families with two point linkage analysis to the USH2A locus on lq41. Additional homozygosity mapping of the affected subjects con cluded with a candidate region of 6.1 Mb. This region spans the previously published candidate region in USH2A. Our study emphasises that the mapped g ene for USH2 is also involved in patients from other populations and will h ave implications for future mutation analysis once the USH2A gene is cloned .