单绒毛膜双羊膜囊双胎之一为45,X/46,XX嵌合体的产前诊断

Prenatal diagnosis of monochorionic-diamniotic twins discordant for 45, X/46, XX mosaicism

目的探讨单绒毛膜双羊膜囊双胎的产前筛查及产前诊断,以及单绒毛膜双羊膜囊双胎之一为嵌合体的形成机理。方法对无创产前筛查提示性染色体异常单绒毛膜双羊膜囊双胎行羊膜腔穿刺,之后对未培养的羊水进行荧光原位杂交检测和单核苷酸多态性微阵列(single nucleotide polymorphism-array, SNP-array),对细胞培养的羊水行G显带核型分析。结果G显带核型胎儿1为46,XX,胎儿2为mos 45,X[11]/46,XX[26]。荧光原位杂交、SNP-array分析显示胎儿2为特纳氏综合征嵌合体,嵌合比约为30%。芯片SNP位点分析证实合子的性质为单绒毛膜双羊膜囊。结论单绒毛膜双羊膜囊双胎在无创性产前检测异常时,建议分别从两个羊膜腔中抽取羊水进行产前诊断,以发现双胎染色体核型不一致的情形。确定45,X/46,XX特纳氏综合征的嵌合比例可为产前遗传咨询提供有价值的信息。

Objective To explore the prenatal screening and diagnosis for a pair of monochorionic-diamniotic (MCDA) twins discordant for 45, X/46, XX mosaicism. Methods Amniotic fluid samples were taken from both twins for whom non-invasive prenatal testing has signaled a high risk for sex chromosomal abnormality. Uncultured amniotic fluid was analyzed by fluorescence in situ hybridization (FISH) and single nucleotide polymorphism array (SNP-array). Conventional G-banded karyotyping analysis was performed on the cultured amniotic fluid. Results Metaphase chromosome analysis showed that one of the twins had a mos 45, X[11]/46, XX[26] karyotype, while the other had a normal karyotype. FISH and SNP-array applied on uncultured amniotic fluid revealed^30% mosaicism in one of the twins. The twins were confirmed to be monozygotic by SNP-array analysis. Conclusion To avoid confusion arising from discordant karyotypes in MCDA twins with abnormal non-invasive prenatal testing (NIPT) results, dual amniocentesis should be carried out to obtain amniotic fluid samples for chromosomal as well as molecular analysis. To determine the ratio of 45, X and 46, XX cells in Turner syndrome can provide valuable information for prenatal genetic counseling.