Abstract:

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.

Key words: Down syndrome, Trisomy, Chimera, Genetic counseling, Karyotyping, In situ hybridization, fluorescence