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 fetal nucleated erythrocytes (NRBCs) could be detected in maternal blood through 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 undergone termination of pregnancy because of fetal trisomy 21 (three cases, 47,XY,+21; four cases, 47,XX,+21). Candidate fetal cells were isolated by flow-sorting by antibodies to the gamma chain of fetal hemoglobin and Hoechst 33342. FISH analysis was performed by the use of chromosome-specific probes for X, Y, and 21. Fetal NRBCs, as defined by the presence of gamma staining, characteristic morphology, and three chromosome 21 signals, along with maternal leukocytes, defined as gamma negative and two chromosome 21 signals, were micromanipulated separately and subjected to fluorescent PCR amplification of chromosome 21 STR markers (D21S11, D21S1411, and/or D21S1412).


RESULTS
In five of seven cases analyzed, fetal NRBCs were aneuploid, as determined 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 aneuploidy and may be useful in the setting of poor hybridization efficiency with FISH analysis. These results suggest that combined fetal aneuploidy and single-gene diagnoses by the use of DNA microarrays may be feasible in the near future.
Samura
O
O
Division of Genetics, Department of Pediatrics, New England Medical Center and Tufts University School of Medicine, 750 Washington Street, Boston, MA 02111, USA.
Sohda
S
S
Johnson
K L
KL
Pertl
B
B
Ralston
S
S
Delli-Bovi
L C
LC
Bianchi
D W
DW
D000782:Aneuploidy; D004314:Down Syndrome / Q000175:diagnosis*; D004900:Erythroblasts / Q000737:chemistry*; D005260:Female; D005312:Fetal Blood / Q000166:cytology*; D006801:Humans; D018895:Microsatellite Repeats; D016133:Polymerase Chain Reaction; D013050:Spectrometry, Fluorescence