ABSTRACT
The Usher syndromes (USH) are autosomal recessive diseases characterised by congenital sensorineural hearing loss and progressive pigmentary retinopathy with or without vestibular dysfunction. At least three distinct loci causing type 1 Usher syndrome (USH1) have been reported, with the USHl locus found in the French-Acadian families of Louisiana (USHlC) mapping to chromosome 11p. In this study 16 microsatellite markers were used to refine the position of the USH1 locus in the French-Acadian population of Louisiana. Two-point linkage analysis showed no recombination between US1C and D11S419 (Zmax = 2.95), D11S902 (Zmax = 6.44), D11S921 (Zmax = 3.31), and D11S899 (Zmax = 5,46). A map of chromosome 11p14-15.1 based on microsatellite markers was developed for use in mapping USH1C. Multipoint linkage analysis gave Z = 6.5 at D11S899 with a one-lod confidence interval covering 5 cM interval. The closest flanking markers showing obligate recombinants are D11S861 and D11S928, which localises USH1C to a 9 cM interval. However, examination of the marker haplotypes in individuals affected by USH1C is consistent with the suggestion that the high icnidence of USH1 in this population is the result of a founder effect and places the USH1C locus in the 5cM interval bounded by D11S861 and D11S899.