Rapid Prenatal Detection Of Down's And 18 Trisomy Syndromes By Quantitative Fluorescent Polymerase Chain Reaction With Short Tandem Repeat Markers

Objective:To explore the possibility of applying the fluorescent polymerase chain reaction with short tandem repeat to detect of Down's and 18 trisomy syndromes,base on this,establish a stable,simple,accurate and rapid prenatal diagnosis technique for Down's and 18 trisomy syndromes in clinic.Method:Quantitative fluorescent PCR amplification was employed to amplify five specific short tandem repeat markers(D21S11,D21S1411,D21S2039,D18S1002, D18S535)located in the Down's syndrome critical region and chromosome 18,respectively, followed by capillary electrophoresis performed on Beckman coulter CEQ8000,and calculation of the relative fluorescence intensities of the PCR product using Genescan software.Result:The result of the 106 samples detected by quantitative fluorescent PCR were same to the samples of karyotype analysis.In this study,samples from normal karyotype individual displayed diallelic peaks of similar fluorescent intensity(1:1)which correspond to two alleles at each STR locus,only a minority of normal samples from homozygous individuals shows a single STR peak.The range of the peak area ratios of the disomic were 1.1-1.2 for D21S11,1.3-1.5 for D21S1411,1.0-1.1 for D21S2039 and D18S1002,1.0-1.2 for D18S535;trisomic samples are expected to fall into two major groups,one group presenting a "triallelic" pattern with three STR peaks of similar intensity with the ratio 1:1:1,corresponding to three different STR alleles,and another group which displaying a "diallelic" pattern of two peaks with ratio of 2:1,corresponding to a double STR allele and another allele,the range of the peak area ratios of the doubled STR allele were 1.4-1.9 for D21S11,1.5-2.0 for D21S1411,1.3-1.6 for D21S2039,1.1-2.1 for D18S1002,1.2-1.4 for D18S535.The median value of the peak area ratio between the normal karyotype samples and the Down's or 18 trisomy syndrome samples was compared used the Wilcoxon rank sum test,there is a significant difference between the normal karyotype samples and the trisomic samples(p＜0.01).Conclusion The results of this study show that quantitative PCR have the advantages of simple,rapid and extensive use,which may be used to rapid prenatal detection the Down's and 18 trisomy syndromes.We can diagnosis the Down's and 18 trisomy syndromes samples according to number of the peak or the range between the normal samples and patients' samples.At the same time,if we detect the sample of amniotic fluid or children's peripheral blood with the sample of parent's peripheral blood,we can know the additional chromosome is from his/her mother or father;And we can judge which period the chromosome non-disjunction was happened,it was happened in the first maiosis or the second maiosis.