Dahoun Sophie, Gagos Sarantis, Gagnebin Maryline, Gehrig Corinne, Burgi Carole, Simon Fabienne, Vieux Chantal, Extermann Philippe, Lyle Robert, Morris Michael A, Antonarakis Stylianos E, Béna Frédérique, Blouin Jean-Louis
Genetic Medicine, University Hospitals of Geneva, Geneva, Switzerland.
Am J Med Genet A. 2008 Aug 15;146A(16):2086-93. doi: 10.1002/ajmg.a.32431.
We report on a monochorionic/diamniotic twin pregnancy discordant for trisomy 21. Amniocentesis (at 13(5/7) weeks) was performed following ultrasound signs of hydrops and cystic hygroma in twin 1 (T1). Prenatal karyotype showed non-mosaic trisomy 21 in T1 (47,XX,+21[7]), and low-grade mosaic trisomy 21 in twin 2 (T2) (47,XX,+21[2]/46,XX[19]). Post mortem examination of fetal skin, kidneys and lungs confirmed trisomy 21 in T1 (47,XX,+21[548]) and the placenta (47,XX,+21[200]). T2 had a normal karyotype (46,XX[648]). Analysis of microsatellite polymorphisms in multiple samples from the placenta, hand, lungs, kidneys and the umbilical cords of both twins confirmed monozygosity for all loci tested, and trisomy 21 in T1. Unexpectedly, T1 and T2 inherited different maternal alleles for markers of the most distal 4 Mbp of 21q. At least four successive events are needed to explain the genetic status of both twins and include maternal MI premature chromatids separation or maternal II meiotic nondisjunction and post-zygotic events such as, chromosome rescue, nondisjunction, an/or recombination.
我们报告了一例21三体综合征不一致的单绒毛膜/双羊膜囊双胎妊娠。在双胎1（T1）出现水肿和囊状水瘤的超声征象后（孕13(5/7)周）进行了羊水穿刺。产前核型显示T1为非嵌合型21三体（47,XX,+21[7]），双胎2（T2）为低度嵌合型21三体（47,XX,+21[2]/46,XX[19]）。对胎儿皮肤、肾脏和肺的尸检证实T1为21三体（47,XX,+21[548]），胎盘为21三体（47,XX,+21[200]）。T2核型正常（46,XX[648]）。对胎盘、双手、肺、肾脏以及双胎脐带的多个样本进行微卫星多态性分析，证实所有检测位点均为单合子，且T1为21三体。出乎意料的是，T1和T2在21号染色体长臂最远端4 Mbp区域的标记物上继承了不同的母本等位基因。至少需要四个连续事件来解释双胎的遗传状态，包括母本MI期早发性染色单体分离或母本II期减数分裂不分离以及合子后事件，如染色体挽救、不分离和/或重组。
