Kalousek D K, Vekemans M
Department of Pathology, University of British Columbia, Yancouver, Canada.
J Med Genet. 1996 Jul;33(7):529-33. doi: 10.1136/jmg.33.7.529.
In most pregnancies the chromosomal complement detected in the fetus is also present in the placenta. The detection of an identical chromosomal complement in both the fetus and its placenta has always been expected as both develop from the same zygote. However, in approximately 2% of viable pregnancies studied by chorionic villus sampling (CVS) at 9 to 11 weeks of gestation, the cytogenetic abnormality, most often trisomy, is confined to the placenta. This phenomenon is known as confined placental mosaicism (CPM). It was first described by Kalousek and Dill in term placentas of infants born with unexplained intrauterine growth restriction (IUGR). Contrary to generalised mosaicism, which is characterised by the presence of two or more karyotypically different cell lines within both the fetus and its placenta, CPM represents tissue specific chromosomal mosaicism affecting the placenta only. The diagnosis of CPM is most commonly made when, after the diagnosis of chromosomal mosaicism in a CVS sample, the second prenatal testing (amniotic fluid culture or fetal blood culture analysis) shows a normal diploid karyotype.
在大多数妊娠中，胎儿检测到的染色体组成也存在于胎盘中。由于胎儿和胎盘均由同一个受精卵发育而来，因此一直以来人们都预期在胎儿及其胎盘中检测到相同的染色体组成。然而，在妊娠9至11周时通过绒毛取样（CVS）研究的约2%的存活妊娠中，细胞遗传学异常（最常见的是三体性）仅限于胎盘。这种现象被称为局限性胎盘嵌合体（CPM）。它最初由卡卢塞克和迪尔在患有不明原因宫内生长受限（IUGR）的婴儿的足月胎盘中描述。与全身性嵌合体不同，全身性嵌合体的特征是胎儿及其胎盘内存在两种或更多种核型不同的细胞系，而CPM代表仅影响胎盘的组织特异性染色体嵌合体。CPM最常见的诊断情况是，在CVS样本中诊断出染色体嵌合体后，第二次产前检测（羊水培养或胎儿血液培养分析）显示正常的二倍体核型。
