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Mitotic stability of fragile X mutations in differentiated cells indicates early post–conceptional trinucleotide repeat expansion

Nature Genetics volume 4, pages 140142 (1993) | Download Citation



We demonstrate hre that somatic variation of CGG repeat length is based on a mosaic of cells with different but stable FMR–1 alleles and does not reflect permanent mitotic instability. The length of a particular allele in an individual cell was maintained in progeny cells establishing a clone. The mutation patterns of multiple repeats in the DNA of fetal tissues were identical and did not significantly change during proliferation in vitro. It is proposed that genotype mosaicism and expansion to full mutation are generated post–conceptionally by the same molecular mechanism in a particular window of early development.

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  1. Abteilung Klinische Genetik, Universität Ulm, Parkstraße 11, D-7900 Ulm, Germany

    • Doris Wöhrle
    • , Ingeborg Hennig
    • , Walther Vogel
    •  & Peter Steinbach


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