Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana, USA.
Genet Med. 2013 Sep;15(9):729-32. doi: 10.1038/gim.2013.26. Epub 2013 Mar 14.
We report on a case in which cell-free fetal DNA was positive for trisomy 13 most likely due to confined placental mosaicism. Cell-free fetal DNA testing analyzes DNA derived from placental trophoblast cells and can lead to incorrect results that are not representative of the fetus.
We sought to confirm commercial cell-free fetal DNA testing results by chorionic villus sampling and amniocentesis. These results were followed up by postnatal chromosome analysis of cord blood and placental tissue.
First-trimester cell-free fetal DNA test results were positive for trisomy 13. Cytogenetic analysis of chorionic villus sampling yielded a mosaic karyotype of 47,XY,+13[10]/46,XY[12]. G-banded analysis of amniotic fluid was normal, 46,XY. Postnatal cytogenetic analysis of cord blood was normal. Karyotyping of tissues from four quadrants of the placenta demonstrated mosaicism for trisomy 13 in two of the quadrants and a normal karyotype in the other two.
Our case illustrates several important aspects of this new testing methodology: that cell-free fetal DNA may not be representative of the fetal karyotype; that follow-up with diagnostic testing of chorionic villus sampling and/or amniotic fluid for abnormal test results should be performed; and that pretest counseling regarding the full benefits, limitations, and possible testing outcomes of cell-free fetal DNA screening is important.
我们报告了一例游离胎儿 DNA 检测提示 13 三体阳性，极有可能是胎盘局限性嵌合体导致的。游离胎儿 DNA 检测分析的是胎盘滋养层细胞的 DNA，可能会导致与胎儿不相符的不正确的检测结果。
我们试图通过绒毛膜取样和羊膜穿刺术来确认商业游离胎儿 DNA 检测结果。随后对脐带血和胎盘组织进行了产后染色体分析。
早孕期游离胎儿 DNA 检测提示 13 三体阳性。绒毛膜取样的细胞遗传学分析显示为嵌合型核型 47,XY,+13[10]/46,XY[12]。羊水的 G 显带分析正常，为 46,XY。脐带血的产后细胞遗传学分析正常。胎盘四个象限的组织核型分析显示，两个象限存在 13 三体嵌合体，另外两个象限的核型正常。
我们的病例说明了这种新检测方法的几个重要方面：游离胎儿 DNA 可能无法代表胎儿核型；对于异常检测结果，应进行绒毛膜取样和/或羊水的诊断性检测；对于游离胎儿 DNA 筛查的充分获益、局限性和可能的检测结果，进行产前咨询很重要。
