产前绒毛染色体核型分析为假阴性的13三体胎儿的遗传学分析

Genetic study of a trisomy 13 fetus with a false-negative karyotype by chorionic villi analysis

目的:探讨1例13三体胎儿产前绒毛染色体核型分析假阴性结果的原因及其可能的形成机制。方法:对1例产前超声提示胎儿多发结构畸形而绒毛染色体核型分析为46,XY的病例,进一步行羊水穿刺进行荧光定量PCR(quantitative fluorescence PCR,QF-PCR)、染色体核型分析及染色体微阵列分析(chromosomal microarray analysis,CMA),以及孕妇外周血胎儿非整倍体的无创产前筛查(non-invasive prenatal testing,NIPT)。应用QF-PCR对引产后的胎盘及胎儿组织进行常见非整倍体检测。结果:羊水QF-PCR、染色体核型分析及CMA结果均显示胎儿核型为47,XY,+13,并且NIPT提示13三体高风险。终止妊娠后胎盘和胎儿组织的QF-PCR结果提示,胎盘母体面及胎儿面右侧为正常核型(XY)和13三体的嵌合体;而胎盘胎儿面(脐带中央区/上/下/左侧)、脐带、羊膜及胎儿肌肉组织为13三体,提示为胎盘嵌合体。结论:绒毛染色体核型分析可能受到胎盘嵌合体的影响而出现假阴性的结果。当绒毛染色体核型与胎儿超声异常表型或NIPT结果不一致时,应考虑羊水或脐血穿刺联合应用多种细胞与分子遗传学技术,以验证绒毛活检结果,降低绒毛染色体核型分析假阴性或假阳性的干扰。

Objective To explore the mechanism of a false-negative result from karyotyping of chorionic villi cells for a trisomy 13 fetus featuring multiple malformations.Methods For a fetus with multiple malformations by ultrasonography and a 46,XY karyotype by chorionic villi analysis,amniocytes were further analyzed with quantitative fluorescence PCR(QF-PCR),G-banded karyotyping and chromosomal microarray analysis(CMA).Meanwhile,non-invasive prenatal testing(NIPT)was conducted on peripheral blood sample from the pregnant woman to determine the chromosomal composition of cytotrophoblast.After induction of labor,common aneuploidies in placenta and fetal tissue were also analyzed by QF-PCR.Results QF-PCR,chromosomal karyotyping and CMA analysis of the amniocytes all suggested complete trisomy 13(47,XY,+13)in the fetus.NIPT also suggested existence of fetal trisomy 13.QF-PCR analysis of the placenta and fetal tissues revealed that cells derived from the maternal surface and right side of fetal surface harbored mosaic trisomy 13,while those derived from other sites of fetal surface of the placenta,umbilical cord,amniotic membrane and fetal muscle tissue harbored trisomy 13.Conclusion Karyotyping of long-term cultured chorionic villus sample may give rise to false negative results due to placental mosaicism.To ensure accurate prenatal diagnosis,discordance between karyotyping of chorionic villi cells,fetal ultrasound and NIPT result should be verified by amniocentesis or cordocentesis and application of multiple cytogenetic and molecular techniques.