Abstract
The fragile X syndrome is the most frequent cause of inherited mental retardation. CGG repeat alleles are usually classified as normal, premutation, or full mutation based on the length of this triplet in the 5′ untranslated region of the FMR1 gene. The pattern of inheritance follows a two-stage intergenerational process in which the premutation evolves into the full mutation. Some reverse mutations have been described, but they appear to be very rare. We describe a family in which a mother of two affected males herself carried a full mutation. Surprisingly, her clinically normal daughter, initially considered to be a carrier by linkage analysis, carried a very short premutation. Findings from our family study corroborate the hypothesis that the expansion during female transmission could be a postzygotic event and raise the problem of mosaicism.
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Acknowledgements
We thank Prof J.L. Mandel for providing the StB12.3 probe and C. Vo Van for technical assistance. This work was supported by INSERM, Assistance Publique de Marseille and by a grant from PHRC 19 (Programme Hospitalier de Recherche Clinique 19).
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Malzac, P., Biancalana, V., Voelckel, M.A. et al. Unexpected Inheritance of the (CGG)n Trinucleotide Expansion in a Fragile X Syndrome Family. Eur J Hum Genet 4, 8–12 (1996). https://doi.org/10.1159/000472163
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DOI: https://doi.org/10.1159/000472163
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