母亲表型正常而反复孕育21-三体综合征患儿的病例非常罕见，临床上要考虑母亲染色体嵌合体的可能。报告1例表型正常孕妇既往4次妊娠早期胚胎停育，其中2次胚胎染色体均为47，XY，+21。夫妻双方染色体正常(计数20个分裂象)。此次妊娠无创产前筛查(noninvasive prenatal testing，NIPT)和扩展型NIPT均提示21-三体高风险，羊水穿刺单核苷酸多态性微阵列(single nucleotide polymorphism array，SNP-array)结果为[arr(1-22)×2，(XN×1)]，胎儿羊水染色体核型为46，XN。复查夫妻双方外周血染色体(计数50个分裂象)，确诊孕妇染色体为47，XX，+21[4]/46，XX[46]，嵌合比例在7％～8％，孕妇外周血染色体荧光原位杂交(fluorescence in situ hybridization，FISH)检测计数100个细胞，7个21-三体，即7％的细胞为21-三体。胎儿羊水FISH检测计数100个细胞均未见21-三体。最终于孕40+1周剖宫产娩一健康女婴。该病例母亲染色体核型为21-三体嵌合型是导致连续2次孕育21-三体综合征患儿的原因。
Genetic Analysis of Second Pregnancy with A Child of 21-Trisomy Syndrome in A Phenotypically Normal Mother
The repeated pregnancies with 21-trisomy syndrome in a phenotypically normal mother are rare,and the possibility of maternal chromosomal mosaic should be considered.We report a woman with normal phenotype who had a history of early embryo loss for 4 times,two of which the karyotypes were 47,XY,+21.The couple's karyotypes were normal(counting 20 split phases).Both noninvasive prenatal testing(NIPT)and extended NIPT results refer to a high risk of trisomy 21,and the amniocentesis single nucleotide polymorphism array(SNP-array)result was[arr(1-22)×2,(XN×1)],and the fetal amniotic fluid karyotype was 46,XN.The repeated peripheral blood chromosomes test for the couple(counting 50 split phases)was performed,the maternal chromosome karyotype was diagnosed as 47,XX,+21[4]/46,XX[46],with a mosaic ratio of 7％-8％.Maternal fluorescence in situ hybridization(FISH)assay in 100 counted cells showed 7 trisomy 21 cells,suggesting that 7％of the cells were trisomy 21.Fetal amniotic fluid FISH test found no 21-trisomy cell.A healthy baby girl was delivered by cesarean section at 40+1 weeks of gestation.In this case,maternal karyotype of a mosaic 21-trisomy cell/normal cell phenotype may contribute to the twice early pregnancy losses with 21-trisomy syndrome.
Down syndromeTrisomyChimeraGenetic counselingKaryotypingIn situ hybridization,fluorescence
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