Peixoto A, dos Santos M R, Seruca R, Amorim A, Castedo S
Instituto de Patologia e Imunologia Molecular da Universidade do Porto, Portugal.
Eur J Hum Genet. 1998 Sep-Oct;6(5):518-22. doi: 10.1038/sj.ejhg.5200204.
In order to look for linkage disequilibrium between the fragile X locus and its flanking markers, we analysed the FRAXAC1 and DXS548 microsatellites in normal and fragile X individuals of Portuguese origin. We observed differences in allele and haplotype frequencies between these two samples. Four haplotypes (A-2, C-2, C-5 and D-6) accounted for 76% of all fragile X chromosomes, whereas a single haplotype (C-7) accounted for 70% of the normal population and less than 3% of the fragile X chromosomes. Among the four observed high-risk haplotypes, A-2 and D-6 had been previously reported in other studies, but C-2 and C-5 seem characteristic of Portuguese patients, as suggested by the high frequency (38%) in fragile X chromosomes and virtual absence in controls. In accordance with previous studies, a greater heterozygosity of the fragile X sample was noted when compared to that of controls. The high frequency of C-7 haplotype in the normal population and its virtual absence in the fragile X sample may reflect the existence of linkage disequilibrium between the two loci and/or selective advantage (protector effect) of this haplotype.
为了寻找脆性X位点与其侧翼标记之间的连锁不平衡，我们分析了葡萄牙裔正常个体和脆性X个体中的FRAXAC1和DXS548微卫星。我们观察到这两个样本之间的等位基因和单倍型频率存在差异。四种单倍型（A-2、C-2、C-5和D-6）占所有脆性X染色体的76%，而单一单倍型（C-7）占正常人群的70%，在脆性X染色体中占比不到3%。在观察到的四种高危单倍型中，A-2和D-6在其他研究中曾有报道，但C-2和C-5似乎是葡萄牙患者的特征性单倍型，脆性X染色体中的高频率（38%）以及在对照中几乎不存在表明了这一点。与先前的研究一致，与对照组相比，脆性X样本的杂合性更高。正常人群中C-7单倍型的高频率以及在脆性X样本中几乎不存在，可能反映了这两个位点之间存在连锁不平衡和/或该单倍型的选择优势（保护作用）。
