Usher syndrome type II (USH2) is characterised by moderate to severe high-frequency hearing impairment, progressive visual loss due to retinitis pigmentosa and intact vestibular responses. Three loci are known for USH2, however, only the gene for USH2a (USH2A) has been identified. Mutation analysis of USH2A was performed in 70 Dutch USH2 families. Ten mutations in USH2A were detected, of which three are novel, c.949C>A, c.2242C>T (p.Gln748X) and c.4405C>T (p.Gln1468X). Including 9 previously published Dutch USH2a families, estimates of the prevalence of USH2a in the Dutch USH2 population were made. Mutations were identified in 62% of the families. In 28% both mutated alleles were identified, whereas in 34% the mutation in only one allele was found. It is estimated that about 28% of the Dutch USH2 families have a different causative gene. Analysis of deduced haplotypes suggests that c.1256G>T (p.Cys419Phe) is a Dutch ancestral mutation, occurring in 16% of the alleles.
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