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H. Vastinsalo, J. Isosomppi, L. Kleemola, L. Jauhola, E.-M. Sankila; Mutation Spectrum of Usher Syndrome in Finland. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2121.
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The epidemiological studies of Usher syndrome (USH) in Finland suggested that the distribution of clinical USH types is 40% USH3, 34% USH1, and 12 % USH2 (14% unknown). We previously detected a USH3A (CLRN1) founder mutation in most patients who were clinically diagnosed with USH3. Due to the considerable overlap of clinical symptoms between the USH types, however, some patients clinically characterized as USH3 did not show CLRN1 mutations. In contrast to USH3A, USH1 is heterogenic in Finland. Recently we detected three novel USH1B mutations in two unrelated Finnish USH1 patients. The purpose of this study was to further investigate the USH mutation spectrum in Finnish patients without previously known USH mutations.
For this study, we analyzed samples from 14 USH patients without previously known mutations using the Asper Genetics USH mutation chip.
From these 14 Finnish USH patients we detected seven different polymorphisms/mutations in heterozygous form: two in MYO7A, and five in USH2A genes. These variations were not previously known to exist in the Finnish population.
Mutation chips are useful in detecting mutations in a heterogeneous disease such as USH. Based on our study, there is considerable heterogeneity of USH1 and USH2 in Finland, in contrast to USH3 which is merely caused by a founder mutation. All seven mutations detected in 14 USH patients were in heterozygous from. We are presently sequencing coding regions of MYO7A and USH2A genes of these patients in order to detect the second mutations.
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