TIGHTLY LINKED FLANKING MICROSATELLITE MARKERS FOR THE USHER SYNDROMETYPE-I LOCUS ON THE SHORT ARM OF CHROMOSOME-II

Usher syndrome type I is an autosomal recessive disease characterized by profound congenital hearing impairment and vestibular dysfunction f ollowed by the onset of progressive pigmentary retinopathy in childhoo d or early adolescence. A locus (USH1C) for one form of this disease w as previously assigned to the short arm of chromosome 11 through linka ge studies in the Acadian population of southwestern Louisiana. Linkag e analyses of a set of microsatellite markers in 27 Acadian families p rovide evidence that USH1C lies between D11S861 and D11S928. Three mar kers (D11S419, D11S921, and D11S899) that lie between the flanking mar kers show no recombination with USH1C, and all 54 chromosomes with the abnormal allele at the disease locus have identical alleles for D11S4 19 and D11S921. This haplotype was found on only 10 of 50 chromosomes with the normal allele at the disease locus, suggesting a strong found er effect. Of the 54 chromosomes with the abnormal allele, 12 had a di vergent allele at D11S899. These results suggest that USH1C is in the 2-3-cM interval between D11S861 and D11S899.