Kalousek D K, Barrett I J, McGillivray B C
Department of Pathology and Medical Genetics, University of British Columbia, Vancouver, Canada.
Am J Hum Genet. 1989 Mar;44(3):338-43.
Cytogenetic analysis of 14 placentas from live newborn infants or from terminated pregnancies with trisomies 13 and 18 revealed that all were mosaic. The mosaicism was confined to the cytotrophoblast and not detected in villous stroma, chorionic plate, or amnion. The percentage of cells with a normal karyotype varied from 12% to 100%, the average being 70%. No such confined mosaicism could be detected in 12 placentas of trisomy 21 fetuses. These findings suggest that a postzygotic loss of a trisomic chromosome in a progenitor cell of trophectoderm facilitates the intrauterine survival of trisomy-13 and -18 conceptuses. They also imply that it is placental function which determines the intrauterine survival and that the mother plays no active role in rejection of trisomic conceptions. The combination of both a pre- and post-zygotic cell division defect in viable trisomy-13 and -18 conceptions points to the possibility of a genetic predisposition to such events. The detection of only a diploid cell line in the cytotrophoblast of some pregnancies with trisomies 13 and 18 also suggests that direct preparation is unreliable for prenatal diagnosis of these trisomies on chorionic villi sampling and that long-term villous culture should be used.
对14例活产新生儿胎盘或13三体和18三体妊娠终止后的胎盘进行细胞遗传学分析发现，所有胎盘均为嵌合体。这种嵌合体局限于细胞滋养层，在绒毛间质、绒毛板或羊膜中未检测到。核型正常的细胞百分比从12%到100%不等，平均为70%。在21三体胎儿的12个胎盘中未检测到这种局限的嵌合体。这些发现表明，滋养外胚层祖细胞中三体染色体的合子后丢失促进了13三体和18三体胚胎的宫内存活。它们还意味着是胎盘功能决定了宫内存活，而母亲在三体胚胎的排斥中不发挥积极作用。存活的13三体和18三体胚胎中合子前和合子后细胞分裂缺陷的结合表明存在遗传易感性导致此类事件发生的可能性。在一些13三体和18三体妊娠的细胞滋养层中仅检测到二倍体细胞系，这也表明直接制片对于绒毛取样产前诊断这些三体不可靠，应采用长期绒毛培养。
