Diagnosis of trisomy 21 in fetal nucleated erythrocytes from maternal blood by use of short tandem repeat sequences

Background: The purpose of this study was to determine whether aneuploid fe tal nucleated erythrocytes (NRBCs) could be detected in maternal blood thro ugh the use of fluorescent PCR amplification with polymorphic short tandem repeat (STR) markers as an alternative or complementary method to analysis by fluorescent in situ hybridization (FISH). Methods: Peripheral blood samples were obtained from women who had just und ergone termination of pregnancy because of fetal trisomy 21 (three cases, 4 7,XY,+21; four cases, 47,XX,+21). Candidate fetal cells were isolated by fl ow-sorting by antibodies to the gamma chain of fetal hemoglobin and Hoechst 33342. FISH analysis was performed by the use of chromosome-specific probe s for X, Y, and 21. Fetal NRBCs, as defined by the presence of gamma staini ng, characteristic morphology, and three chromosome 21 signals, along with maternal leukocytes, defined as gamma negative and two chromosome 21 signal s, were micromanipulated separately and subjected to fluorescent PCR amplif ication of chromosome 21 STR markers (D21S11, D21S1411, and/or D21S1412). Results: In five of seven cases analyzed, fetal NRBCs were aneuploid, as de termined by the presence of triallelic or diallelic peaks of chromosome 21 sequences when compared with sequences from the maternal leukocytes. Conclusions: Fluorescent PCR amplification of STRs can detect fetal aneuplo idy and may be useful in the setting of poor hybridization efficiency with FISH analysis. These results suggest that combined fetal aneuploidy and sin gle-gene diagnoses by the use of DNA microarrays may be feasible in the nea r future. (C) 2001 American Association for Clinical Chemistry.