Parrish J E, Oostra B A, Verkerk A J, Richards C S, Reynolds J, Spikes A S, Shaffer L G, Nelson D L
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030.
Nat Genet. 1994 Nov;8(3):229-35. doi: 10.1038/ng1194-229.
Three folate-sensitive fragile sites, termed FRAXA, FRAXE and FRAXF, have been identified on the distal end of chromosome Xq. The first two contain expanded, hypermethylated and unstable CGG (or GCC) repeats within CpG islands. We now report the isolation of similar sequences responsible for the third fragile site, FRAXF. A 5-kilobase EcoRI fragment derived from a cosmid coincident with the cytogenetic anomaly detects expanded, methylated and unstable sequences in five individuals who exhibit fragile sites in distal Xq; these individuals have normal repeat lengths at both FRAXA and FRAXE. By sequence analysis, the expanded region contains a GCC repeat. PCR and sequence analysis of chromosomes from the general population indicates that the repeat is polymorphic (6 to 29 triplets), and is stable upon transmission.
在X染色体长臂（Xq）远端已鉴定出三个对叶酸敏感的脆性位点，分别称为FRAXA、FRAXE和FRAXF。前两个位点在CpG岛内含有扩增的、高度甲基化且不稳定的CGG（或GCC）重复序列。我们现在报告了导致第三个脆性位点FRAXF的类似序列的分离情况。一个源自与细胞遗传学异常相符的黏粒的5千碱基EcoRI片段，在五个在Xq远端表现出脆性位点的个体中检测到了扩增的、甲基化且不稳定的序列；这些个体在FRAXA和FRAXE处的重复长度均正常。通过序列分析，扩增区域包含一个GCC重复序列。对普通人群染色体的PCR和序列分析表明，该重复序列具有多态性（6至29个三联体），且在传递过程中稳定。
