Cell
Volume 74, Issue 1, 16 July 1993, Pages 127-134
Journal home page for Cell

Article
Trinucleotide repeat amplification and hypermethylation of a CpG island in FRAXE mental retardation

https://doi.org/10.1016/0092-8674(93)90300-FGet rights and content

Abstract

We have cloned the fragile site FRAXE and demonstrate that individuals with this fragile site possess amplifications of a GCC repeat adjacent to a CpG Island in Xq28 of the human X chromosome. Normal individuals have 6–25 copies of the GCC repeat, whereas mentally retarded, FRAXE-positive individuals have >200 copies and also have methylation at the CpG island. This situation is similar to that seen at the FRAXA locus and is another example in which a trinucleotide repeat expansion is associated with a human genetic disorder. In contrast with the fragile X syndrome, the GCC repeat can expand or contract and is equally unstable when passed through the male or female line. These results also have implications for the understanding of chromosome fragility.

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