Detection Fetal DNA From Maternal Peripheral Blood And The Application Of Fetal DNA In Noninvasive Prenatal Diagnosis For Down's Syndrome

Objective: To detect the time of appearance and disappearance of free fetal DNAfrom peripheral blood of pregnant women and to explore the possibility of non-invasive prenatal gene diagnosis for Down's syndrome by using fetal DNA from the maternalcirculation. Methods: (1) Y-specific sequence (SRY gene) of DNA samples from 63pregnancies were detected by polymerase chain reaction(PCR). (2) short tandem repeats(STRs) loci (D21S11, D21S1411, D21S1412, D21S1414) in and near the region (21q22.1-21q22.2 ) on 21 chromosome of DNA samples from the control, patients diagnosed as Down's syndrome and all pregnancies were analyzed by PCR ,no-degeneration polyacrylamide gel electrophoresis , silver staining . (3)4 SIR loci of pregnancies having high risk of Down's syndrome were analysized forprenatal diagnosis . Results: (1)Y-chromosome-specific DNA was detected in allpregnancies with a male fetus. The earliest detection was at 7 weeks and the latest at 12 weeks. Y-chromosome-sequence was no longer detected in any of the male pregnancies 2 hours after delivery. The ratios of the detection among different gestational trimesters were 4/11, 9/11, 11/11. No Y-chromosome-sequence was detected in any of the pregnancies with a female fetus. This demonstrated that fetal DNA appears in the maternal circulation early in the first trimester. There weren't the problems of contamination from previous pregnancies. (2) 6/8, 7/8, 3/8, 7/8 of normal people showed two bands with a DNA content ratio of 1:1 and 2/8, 1/8, 5/8, 1/8 of normal people showed one band in 4 loci, respectively. (3)7/11, 8/11, 6/11, 7/11 of all patients showed two bands with a DNA content ratio of 2:1; 3/11, 2/11, 2/11, 3/11 showed three bands with a DNA content ratio of 1:1:1 and 1/11, 1/11, 3/11, 1/11 showed one band.(4) Fetal paternal inherited allele of 4 STRs loci can be detected from 63 pregnant women.The ratios of pregnancies samples detected a fetal-specific band were 58/63. 56/63. 16/63. 56/63 in 4 loci respectively. (5)There were no abnormal bands observed on 4 loci of DNA samples from pregnancies of high risk having Down's syndrome fetus.Conclusions: (1)fetal DNA is present in maternal plasma and serum. It can bedetected in the first trimester The concentration of fetal DNA in maternal circulation increased with gestational ages. (2) The 4 selected loci have high polymorphism and they can provide much polymorphotic information, fetal DNA can be detected from maternal circulation by amplifying STRs loci on 21 chromosome. (3)About 91.7%, 91.7%, 75% and 91.7% patients were detected correctly with D21S11, D21S1411, D21S 1412, D21S1414, respectively. All patients were detected correctly by combining with 4 loci are valuable gene markers for gene diagnosis of Down's syndrome. (3)No abnormal bands were observed on the detected of pregnancies of high risk having a Down's syndrome fetus. It is significant to the prenatal diagnosis of Down's syndrome by using 4 loci of fetal DNA extracted from maternal plasma and serum .