The USH1C 216G→A mutation and the 9-repeat VNTR(t,t) allele are in complete linkage disequilibrium in the Acadian population
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Recently, mutations in USH1C were shown to be associated with Usher syndrome type IC, and a mutation (216G→A) in exon 3 was identified in an Acadian family. In addition, a 45-bp variable number of tandem repeat (VNTR) polymorphism was found in intron 5 of USH1C. Polymerase chain reaction amplification of the VNTR region and restriction enzyme analysis of exon 3 of USH1C showed that, of 44 Acadian patients, 43 were homozygous for both the 216G→A mutation and nine repeats of the VNTR, with a "t" nucleotide replacing a "g" nucleotide at the 8th position of both the eighth and ninth copies of the repeat, viz., 9VNTR(t,t). The remaining Acadian patient was reported to be a compound heterozygote for 216G→A/9VNTR(t,t) and 238–239insC, a USH1C mutation that has been found in other populations. These data demonstrate that the 9VNTR(t,t) allele is in complete linkage disequilibrium with the 216G→A mutation in the Acadian population. Among 82 Acadian controls, one was heterozygous for 216G→A/9VNTR(t,t). The 238–239insC mutation was not found in Acadian controls. Analysis of 340 non-Acadian normal samples showed the presence of a 9-repeat VNTR allele in one Hispanic sample. This individual had neither the 216G→A mutation nor the Acadian VNTR(t,t) structure. These results suggest that the 216G→A mutation and the 9VNTR(t,t) allele are restricted to the Acadians and are in complete linkage disequilibrium.
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