Isolation of Fetal Cells in Maternal Peripheral Blood and Genetic Analysis of Trisomy 21 by GPA-immuno FISH(Fluorescence in situ hybridization

Kim, Sung Hoon; Yang, Young Ho; Cho, Dong Jae; Kim, Sae Kwang; Park, Yong Won; Kim, In Kyu; Lee, Yoon Ho; Kim, Mi Sun; Nam, Myung Sook

Abstract

INTRODUCTION: Down's syndrome is the most common congenital chromosomal anomalies which occurs 1 out of 700-1000 births. Until now, for prenatal diagnosis of Trisomy 21, invasive techniques such as amniocentesis, chorionic villus sampling(CVS) and cordocentesis were used, but they encompass the rare possibility of morbidity to the mother and fetus. Triple marker using maternal serum is a currently used noninvasive method, but it only shows the accuracy of 60%. Accordingly, a noninvasive method, using fetal cells from maternal blood is under extensive investigation. This study was undertaken to establish a noninvasive prenatal genetic diagnostic method of trisomy 21 using fetal nRBCs rarely present in maternal circulation.
MATERIALS AND METHODS
Peripheral venous blood samples were collected from 76 women and treated by heparin. For the isolation of fetal cells, we used a triple density gradient centrifugation, and Vario-MACS and Mini-MACS using CD45 and CD71, and then, the morphological differentiation of the fetal nRBC was performed by Kleihaur-Betke stain. With GPA immunostain, nRBCs were identified by cytoplasm and GPA attatchment, and after marking the site, a FISH was performed.
RESULTS
This study population included 76 patients from 8 to 41 weeks of gestation, and nRBC was separated from all cases. The morphological differentiation was achieved by K-B stain. The mean number of nRBC collected from 20 ml of maternal peripheral blood was 15. The number of nRBCs retrieved reached its peak in 12-18 gestational weeks(18.9 6.0) which decreased from 20 gestational weeks and thereafter. Fetal sex was determined by FISH analysis using probe X, Y with GPA-immunostained cells. GPA-immuno FISH analysis using probe 21 in 30 cases of advanced maternal age or positive triple markers, we confirmed 3 cases of Down's syndrome. These results were also confirmed using the CVS or amniocentesis.
CONCLUSIONS
Fetal nRBCs were separated from all cases after 8 gestational weeks. Prenatal diagnosis of trisomy 21 through GPA-immuno FISH analysis of chromosome 21 using separated fetal nRBCs is an useful, innovative, accurate, rapid and non-invasive diagnostic method. But for clinical use, more cases of experiments will be needed.