Hassold T, Merrill M, Adkins K, Freeman S, Sherman S
Department of Genetics, Case Western Reserve University, Cleveland, OH 44106-4955, USA.
Am J Hum Genet. 1995 Oct;57(4):867-74.
Trisomy 16 is the most common human trisomy, occurring in > or = 1% of all clinically recognized pregnancies. It is thought to be completely dependent on maternal age and thus provides a useful model for studying the association of increasing maternal age and nondisjunction. We have been conducting a study to determine the parent and meiotic stage of origin of trisomy 16 and the possible association of nondisjunction and aberrant recombination. In the present report, we summarize our observations on 62 spontaneous abortions with trisomy 16. All trisomies were maternally derived, and in virtually all the error occurred at meiosis I. In studies of genetic recombination, we observed a highly significant reduction in recombination in the trisomy-generating meioses by comparison with normal female meioses. However, most cases of trisomy 16 had at least one detectable crossover between the nondisjoined chromosomes, indicating that it is reduced--and not absent--recombination that is the important predisposing factor. Additionally, our data indicate an altered distribution of crossing-over in trisomy 16, as we rarely observed crossovers in the proximal long and short arms. Thus, it may be that, at least for trisomy 16, the association between maternal age and trisomy is due to diminished recombination, particularly in the proximal regions of the chromosome.
16三体是人类最常见的三体，在所有临床确诊的妊娠中发生率≥1%。它被认为完全取决于母亲的年龄，因此为研究母亲年龄增加与不分离之间的关联提供了一个有用的模型。我们一直在进行一项研究，以确定16三体的亲本和减数分裂起源阶段，以及不分离与异常重组之间可能的关联。在本报告中，我们总结了对62例16三体自然流产病例的观察结果。所有三体均源自母亲，并且几乎所有错误都发生在减数分裂I期。在基因重组研究中，与正常女性减数分裂相比，我们观察到产生三体的减数分裂中重组显著减少。然而，大多数16三体病例在不分离的染色体之间至少有一个可检测到的交叉，这表明是重组减少——而不是没有重组——是重要的诱发因素。此外，我们的数据表明16三体中交叉的分布发生了改变，因为我们很少在近端长臂和短臂中观察到交叉。因此，至少对于16三体来说，母亲年龄与三体之间的关联可能是由于重组减少，特别是在染色体的近端区域。
