Summary
The IQ levels of 18 female carriers with the marker X chromosome were evaluated, and cytogenetic studies after BrdU incorporation were performed. A highly significant correlation between mental capacity and replication pattern of the X chromosomes could be demonstrated. Heterozygous females with normal intelligence showed a clear tendency to carry the fragile site at the late replicating X chromosome, while other female carriers with lower intelligence or mental impairment expressed their fragile site mainly with the early replicating X chromosome. This observation could be interpreted as an expression of Lyonisation.
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Paul, J., Froster-Iskenius, U., Móje, W. et al. Heterozygous female carriers of the marker-X-chromosome: IQ estimation and replication status of fra(X)(q). Hum Genet 66, 344–346 (1984). https://doi.org/10.1007/BF00287638
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DOI: https://doi.org/10.1007/BF00287638