Sjl. Knight et al., TRIPLET REPEAT EXPANSION AT THE FRAXE LOCUS AND X-LINKED MILD MENTAL HANDICAP, American journal of human genetics, 55(1), 1994, pp. 81-86
We have recently shown that the expression of the FRAXE fragile site i
n Xq28 is associated with the expansion of a GCC trinucleotide repeat.
In the families studied, FRAXE expression is also associated with mil
d mental handicap. Here we present data on families that previously ha
d been diagnosed as having the fragile X syndrome but that later were
found to be negative for trinucleotide repeat expansion at the FRAXA l
ocus. In these families we demonstrate the presence of a GCC trinucleo
tide repeat expansion at the FRAXE locus. Studies of the FRAXE locus o
f normal individuals show that they have 6-25 copies of the repeat, wh
ereas affected individuals have >200 copies. As in the fragile X syndr
ome, the amplified CpG residues are methylated in affected males.