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 sensorineural hearing loss. Usher syndrome is estimated to account for 6-10% of all congenital sensorineural hearing loss. A gene locus in Usher type II (USH2) families has been assigned to a small region on chromosome 1q41 called the UHS2A locus. We have investigated two families with Usher syndrome from different isolated populations. One family is a Norwegian Saami family and the second family is from the Cayman Islands. They both come from relatively isolated populations and are inbred families suitable for linkage analysis. A lod score of 3.09 and 7.65 at zero recombination was reached respectively in the two families with two point linkage analysis to the USH2A locus on 1q41. Additional homozygosity mapping of the affected subjects concluded with a candidate region of 6.1 Mb. This region spans the previously published candidate region in USH2A. Our study emphasises that the mapped gene for USH2 is also involved in patients from other populations and will have implications for future mutation analysis once the USH2A gene is cloned.