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产前诊断中有0.6‰～2‰的病例能发现小的额外标记染色体,这种新生的额外标志的染色体不能用标准的细胞遗传技术来识别,预测羊水(AF)标本中这种额外标记染色体的发生率约为1/2 500,母亲年龄越大则发生率越高。已经发现70％非卫星标志染色体的病例中有这种额外标志染色体与正常细胞相嵌合。在产前诊断工作中,当发现一条新生的、额外的小标志染色体时,要预言畸形的风险很困难。然而,如果知道其起源,查找有关文献记载的某些有特征性显型的标志染色体的资料,就能较容易地预测发生畸形的风险,以便更准确地判断预后。但是,在羊水标本中
In the prenatal diagnosis of 0.6 ‰ to 2 ‰ cases can be found in small additional marker chromosomes, this new extra marker chromosomes can not be identified using standard cytogenetic techniques to predict this extra marker chromosome in amniotic fluid (AF) specimens The incidence of about 1/500, the older mother, the higher the incidence. It has been found that in 70% of non-satellite marker chromosome cases this extra marker chromosome is chimeric to normal cells. In prenatal diagnosis, when a new, extra small marker chromosome is found, it is difficult to predict the risk of deformity. However, knowing its origin and looking for information on some of the documented phenotypic marker chromosomes makes it easier to predict the risk of deformity in order to make a more accurate prognosis. However, in amniotic fluid specimens