QF-PCR检测性染色体不同的同卵双胎一例分析

Monozygotic twin fetuses discordant for sex chromosomes detected by QF-PCR

目的探讨同卵双胎染色体异常产前检测的最适样本类型及同卵双胎的发生机制。方法对1例因唐氏筛查高风险的双胎妊娠孕妇行羊膜腔穿刺取羊水样本,用定量荧光PCR(quantitative fluorescent PCR,QF-PCR)检测常见染色体非整倍体,核型分析方法检测染色体病。结果 QF-PCR提示双胎为同卵双胎,胎儿A性染色体为:XY,胎儿B性染色体为:XO;染色体核型分析结果显示胎儿A为:46,XY,胎儿B为:45,XO。两种检测方法均未检测到任何一胎羊水样本有:46,XY/45,XO嵌合现象。结论在产前诊断中,羊水样本比绒毛及脐血样本更适合用于同卵双胎胎儿的染色体检测。胚胎发育早期部分细胞染色体分离错误导致胚胎出现两个染色体不同的细胞系可能是同卵双胎发生的重要原因。

Objective：To discuss the optimum sample types for detecting true karyotypes in monozygotic twins during prenatal stage and potential mechanisms that may give rise to discordant karyotypes in monozygous twins. Methods： Amniocentesis was performed and amniotic fluid was collected from each gestational sac of a twins pregnancy woman with high risk of Down syndrome. Using fluorescence quantitative PCR （quantitative fluorescent PCR, QF-PCR） to detect common chromosome aneuploidy and karyotype analysis to detect chromosome disease. Results= QF-PCR showed the twins were Monozygotic twins, Twin A＇s sex chromosome was XY while twin A was homogeneous monosomy X. Cytogenetic analysis showed win A was 46,XY and Twin B was 45,X. Mosaicism was not detected from any of the twins by both methods. Conclusions= Amniocytes would be a more suitable for karyotyping in monozygotic twins compared with fetal blood or chorionic villi for prenatally diagnosis. Development of a discordant cell line early in development may be a cause for human monozygotic twinning.