Nikitina T V, Nazarenko S A
Research Institute of Medical Genetics, Tomsk Scientific Center, Russian Academy of Medical Sciences, Russia.
Genetika. 2000 Jul;36(7):965-71.
In the analysis of tetranucleotide DNA repeats inheritance carried out in 55 families with a history of spontaneous miscarriages and normal karyotypes in respect to 21 loci located on seven autosomes, 8 embryos (14.5%) demonstrating 12 cases of the presence of alleles absent in both parents were described. The study of chromosome segregation using other DNA markers permitted highly probable exclusion of false paternity as well as uniparental disomy as the reasons for parent/child allele mismatches. The high probability of paternity together with the presence of a "new" allele at any offspring locus points to the mutation having occurred during game-togenesis in one of the parents. Examination of mutation in spontaneous abortuses revealed an increased number of tandem repeat units at microsatellite loci in three cases and an decreased number of these repeats in six cases. In two abortuses, a third allele absent in both parents, which resulted from a somatic mutation that occurred during embryonic development, was observed. The prevalence of the male germline mutations, revealed during investigation of the mutation origin, was probably associated with an increased number of DNA replication cycles in sperm compared to the oocytes. In spontaneous abortuses, the mean mutation rate of the tetranucleotide repeat complexes analyzed was 9.8 x 10(-3) per locus per gamete per generation. This was about five times higher than the spontaneous mutation rate of these STR loci. It can be suggested that genome instability detected at the level of repeated DNA sequences can involve not only genetically neutral loci but also active genomic regions crucial for embryonic viability. This results in cell death and termination of embryonic development. Our findings indicate that the death of embryos with normal karyotypes in most cases is associated with an increased frequency of germline and somatic microsatellite mutations. The data of the present study also provide a practical tool for the quantitative evaluation of this phenomenon and for the analysis of the reasons for miscarriages and embryonic death in certain families.
在对55个有自然流产史且21号常染色体核型正常的家族进行的四核苷酸DNA重复序列遗传分析中，涉及位于7条常染色体上的21个位点，共描述了8个胚胎（14.5%）出现12例双亲中均不存在的等位基因。使用其他DNA标记对染色体分离进行研究，极有可能排除假父系以及单亲二体性作为亲子等位基因不匹配的原因。高父系概率以及任何后代位点出现“新”等位基因表明，突变发生在双亲之一的配子发生过程中。对自然流产胚胎中的突变进行检测发现，3例微卫星位点的串联重复单位数量增加，6例这些重复序列数量减少。在2例流产胚胎中，观察到双亲中均不存在的第三个等位基因，这是由胚胎发育过程中发生的体细胞突变导致的。在对突变起源的研究中发现的男性生殖系突变的普遍性，可能与精子中DNA复制周期数量相比卵母细胞增加有关。在自然流产胚胎中，所分析的四核苷酸重复序列复合体的平均突变率为每代每个配子每个位点9.8×10⁻³。这比这些STR位点的自发突变率高约5倍。可以推测，在重复DNA序列水平检测到的基因组不稳定性不仅可能涉及遗传中性位点，还可能涉及对胚胎活力至关重要的活跃基因组区域。这导致细胞死亡和胚胎发育终止。我们的研究结果表明，大多数情况下核型正常的胚胎死亡与生殖系和体细胞微卫星突变频率增加有关。本研究的数据还为定量评估这一现象以及分析某些家族中流产和胚胎死亡的原因提供了实用工具。
