Detectionof Fetal Trisomy 8 Mosaicism with Cell-free Fetal DNA in Maternal Plasma

Background: Cell-free fetal DNA in the maternal plasma is widely used to identify the aneuploid, including trisomy 21, 18, 13 and sex chromosomes. While for the detection of rare autosomal trisomies, the outcome has not come to a consensus. Here we reported a case of trisomy 8 mosaicism (T8M) which was identified by cffDNA screening. Methods Noninvasive prenatal screening (NIPS), fetal karyotyping, single nucleotide polymorphism array (SNP array) and interphase fluorescence in situ hybridization (FISH) analysis were used to characterize etiology in the fetus. Results In this study, trisomy 8 was initially identified by cell-free fetal DNA in the maternal plasma. Ultrasound scans and magnetic resonance imaging observed fetal hydronephrosis and irregular spine. Trisomy 8 mosaicism was diagnosed based on the SNP array and amniocentesis results. The couple decided to continue the pregnancy after genetic counseling and a male infant was delivered. Interphase FISH analysis in the uncultured neonatal cord blood cells confirmed trisomy 8 mosaicism, with a percentage of 10%. In the follow up, periodic fever as well as language retardation was observed, indicating a poor prognosis. Conclusions Our study provided an insight into the identification of low level rare autosomal trisomy mosaicism with cell-free fetal DNA.