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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.

Type

Journal article

Journal

Cell

Publication Date

16/07/1993

Volume

74

Pages

127 - 134

Keywords

Base Sequence, Fragile X Syndrome, Gene Amplification, Humans, Intellectual Disability, Methylation, Molecular Sequence Data, Pedigree, Repetitive Sequences, Nucleic Acid, X Chromosome