一个大家族中的脆性X综合征。III. 侧翼DNA标记与脆性位点Xq27的连锁研究。
The fragile X syndrome in a large family. III. Investigations on linkage of flanking DNA markers with the fragile site Xq27.
作者信息
Veenema H, Carpenter N J, Bakker E, Hofker M H, Ward A M, Pearson P L
出版信息
J Med Genet. 1987 Jul;24(7):413-21. doi: 10.1136/jmg.24.7.413.
In a large family with the fragile X syndrome, we performed linkage investigations with six probes, detecting RFLPs at both sides of the fragile site Xq27. The nearest flanking markers were cX55.7 (DXS105) on the centromeric side (theta = 0.04, lod 5.0) and St14 (DXS52) on the telomeric side (theta = 0.08, lod 4.0). Non-penetrance could be shown by the presence of the grandpaternal X chromosome in three mentally retarded fra(X) positive males. A second non-penetrant male in this family had inherited an abnormal grandmaternal X chromosome. His carrier mother had two retarded fra(X) positive brothers. Intermediate between the non-penetrant and fully penetrant males was a non-retarded male, who expressed the fragile site in 6% of his cells. His X chromosome showed the same polymorphisms as were found in his seven severely retarded brothers. In five fra(X) negative females the presence of an abnormal X chromosome could be demonstrated. Despite the existence of non-penetrance in this pedigree, there was no close linkage between a factor IX polymorphism and the fragile site (theta = 0.16, lod 1.9). However, in six descendants of a non-penetrant male, the change to penetrance appeared to be accompanied by a low recombination frequency for flanking markers.
在一个患有脆性X综合征的大家庭中，我们用六个探针进行了连锁研究，检测脆性位点Xq27两侧的限制性片段长度多态性（RFLP）。最靠近的侧翼标记在着丝粒侧是cX55.7（DXS105）（θ = 0.04，优势对数5.0），在端粒侧是St14（DXS52）（θ = 0.08，优势对数4.0）。在三名智力发育迟缓的脆性X阳性男性中存在祖父的X染色体，这表明存在不外显现象。这个家族中的另一名不外显男性继承了一条异常的祖母X染色体。他的携带者母亲有两个智力发育迟缓的脆性X阳性兄弟。在不外显男性和完全外显男性之间的是一名智力正常的男性，他6%的细胞表达了脆性位点。他的X染色体显示出与他的七个严重智力发育迟缓的兄弟相同的多态性。在五名脆性X阴性女性中，可以证明存在异常的X染色体。尽管这个家系中存在不外显现象，但因子IX多态性与脆性位点之间没有紧密连锁（θ = 0.16，优势对数1.9）。然而，在一名不外显男性的六个后代中，外显率的改变似乎伴随着侧翼标记的低重组频率。
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