Nieuwint A, Van Zalen-Sprock R, Hummel P, Pals G, Van Vugt J, Van Der Harten H, Heins Y, Madan K
Department of Clinical Genetics, University Hospital Vrije Universiteit, Amsterdam, The Netherlands.
Prenat Diagn. 1999 Jan;19(1):72-6. doi: 10.1002/(sici)1097-0223(199901)19:1<72::aid-pd465>3.0.co;2-v.
A chromosomal abnormality in one of the fetuses of a monozygotic twin pregnancy is a rare phenomenon. In the prenatal unit of our cytogenetics laboratory we have recently come across two such heterokaryotypic twin pregnancies. In both cases ultrasound abnormalities were detected in one fetus of each twin pair. Chromosomal analysis showed that one twin pregnancy was discordant for trisomy 21 and the other for 45,X. Ultrasonographic examination suggested a monochorionic twin pregnancy in each case and DNA studies confirmed that both sets of twins were monozygotic. Both pregnancies were terminated. Biopsies taken from different sites of the placentas showed chromosomal mosaicism in both cases. There was no clear correlation between the karyotype found close to the site of the umbilical cord insertion in the placenta and the karyotype of the fetus. Sampling of amniotic fluid from both sacs is recommended in diamniotic twin pregnancies if one (or both) of the fetuses has ultrasound abnormalities, even if the twins are apparently monochorionic.
单卵双胎妊娠中一个胎儿出现染色体异常是一种罕见现象。在我们细胞遗传学实验室的产前科室，最近遇到了两例这种核型不同的双胎妊娠。在这两例中，每对双胞胎中的一个胎儿都检测到超声异常。染色体分析显示，一对双胞胎妊娠中一个为21三体不和谐，另一个为45,X不和谐。超声检查提示每例均为单绒毛膜双胎妊娠，DNA研究证实两组双胞胎均为单卵双胎。两例妊娠均终止。从胎盘不同部位取的活检显示两例均有染色体嵌合现象。在胎盘脐带插入部位附近发现的核型与胎儿核型之间没有明显的相关性。在双羊膜囊双胎妊娠中，如果一个（或两个）胎儿有超声异常，即使双胞胎显然是单绒毛膜的，也建议从两个羊膜囊中抽取羊水样本。
