Confirmation of the prenatal mosaic trisomy 2 via fetal USG and cytogenetic analyses

The birth of a baby with mosaicism resulting from a known mosaic embryo transfer: a case report

Mosaic embryos have the potential to implant and develop into healthy babies. The transfer of mosaic embryos is now considered to be a possible option for women undergoing ART with preimplantation genetic testing for aneuploidies and in the absence of euploid embryos, particularly those with diminished ovarian reserve and/or advanced maternal age. It can aid in avoiding the discard of potentially viable embryos, which might otherwise result in healthy babies. In over 500 studies on mosaicism, there have been no reports of mosaicism in babies born following the transfer of mosaic embryos. Here, we present a case report of a 39-year-old woman with diminished ovarian reserve with only one blastocyst available for trophectoderm biopsy. The transfer of the embryo, which showed 35% mosaicism of monosomy 2, resulted in pregnancy. Amniocentesis revealed a mosaic trisomic mos46,XX(98)/47,XX,+2(2) karyotype. There were no pathological findings in detailed ultrasonography, and the fetus showed a normal fetal growth with no evidence of intrauterine growth retardation. A healthy female baby was born at Week 37. The peripheral blood chromosome analysis validated with fluorescence in situ hybridization showed 2% mosaic monosomy 2 [mos45,XX,-2(2)/46,XX(98)]. This is the first reported case of true fetal mosaicism resulting in a live birth following the transfer of a known mosaic embryo. Worldwide, prenatal diagnosis has shown the depletion of mosaicism in embryos transferred after they have been reported as mosaics. Our case demonstrates the need for close prenatal monitoring and diagnosis by early amniocentesis, preferably at >14 weeks gestation.

Prenatal diagnosis of mosaic trisomy 2 and literature review

Background

We presented two cases of mosaic trisomy 2 with high risk of maternal serum screening and non-invasive prenatal testing (NIPT). The invasive amniocentesis was performed and genetic tests including karyotype, single nucleotide polymorphism array(SNP-array), interphase fluorescence in situ hybridization (FISH) were employed to detect the chromosomal abnormality.

Results

Cytogentic analysis of the case 1 and 2 showed a mosaic karyotype consisting of two cell lines (mos 47,XY,+2[8]/46,XY[19] and mos 47,XX,+2[7]/46,XX[28], respectively). SNP-array using DNA extracted from uncultured amniotic fluid cells revealed a result of arr[GRCh38](2)x2~3, which indicated that chromosome 2 may be trisomy of mosaicism in both two cases. The results of interphases FISH confirmation test showed that three red signals of the CEP 2 specific probe in 14%(14/100) and 12%(12/100) of the two cases’ cells, respectively, which indicated a mosaicism for trisomy 2 in the uncultured amniocytes. Fetal ultrasound of case 1 suggested that the long bone is smaller than the gestational age, while the case 2 showed that the biparietal diameter (BPD), head circumference (HC) and femur length (FL) were smaller than gestational age along with abnormal cardiac structure.

Conclusions

We presented two cases with mosaic trisomy 2 and performed confirmatory genetic testing using cultured and uncultured amniocytes. When maternal serum screening and NIPT suggesting high risk, genetic counselor should be alert for increasing possibility of chromosomal anomalies if combined with abnormal ultrasound findings.