20三体嵌合体:细胞和分子遗传学产前诊断技术的差异

Mosaic trisomy 20:discrepancy between cyto-and molecular genetic technologies in prenatal diagnosis

目的通过对一例高龄孕妇的产前诊断,为20三体嵌合体的遗传咨询和产前诊断提供依据。方法应用染色体核型分析、染色体微阵列分析(chromosomal microarray analysis,CMA)及荧光原位杂交(fluorescence in situ hybridization,FISH)技术对一名43岁孕妇行胎儿的产前诊断。结果胎儿羊水细胞染色体核型为47,XN,+20。CMA检测结果未见异常。核型分析和CMA技术结果存在差异。在验证样本一致性实验中,发现羊水细胞培养前后两次CMA检测结果不一致。培养之前CMA结果未见异常,与核型结果不一致;培养之后为47,XN,+20,与核型结果一致。羊水细胞FISH检测结果为nuc ish(D20Z1)×3[11]/(D20Z1)×2[89],即胎儿约有11%的细胞为20号染色体三体。患儿出生后外周血染色体核型分析未见异常。结论该例胎儿羊水样本可能为20三体嵌合体,培养过程中47,XN,+20细胞可能存在优势生长,导致羊水细胞组成的变化。胎儿FISH检测提示的20三体嵌合体可能来自于胎盘非限制性嵌合或患儿的体细胞20三体嵌合体。

Objective To provide genetic counseling and prenatal diagnosis for a fetus with mosaic trisomy 20.Methods Chromosomal karyotyping,chromosomal microarray analysis(CMA)and fluorescence in situ hybridization(FISH)were carried out for a pregnant woman with advanced maternal age.Results The karyotype of amniotic fluid sample was 47,XN,+20,whilst the result of CMA was normal.To verify this discrepancy,CMA was performed again with the cultured amniotic fluid,which yielded a result of 47,XN,+20.FISH assay of the amniotic fluid sample was nuc ish(D20Z1)×3[11]/(D20Z1)×2[89],which indicated that about 11%of fetal cells were trisomy 20.After the fetus was born,the karyotype of peripheral blood sample was normal.Conclusion The amniotic fluid sample might be mosaic trisomy 20,and a dominant growth of 47,XN,+20 cells had occurred during the culture process,resulting in alteration of amniotic fluid cell composition.Mosaic trisomy 20 indicated by FISH may be attributed to confined placental mosaicism or somatic mosaicism of trisomy 20.