Appolication Of STR-PCR In Diagnosis Of Down Syndrome

ObjectiveDown's syndrome,whose another name is trisomy 21,is the most common congenital chromosome aneuploidies and its incidence reaches to 0.13%at present. The incidence of DS remains in high level every year in China,which gives heavy burden to family and country.However,karyotype analysis applicated clinically can not be used in common laboratory,and also not be fit to large scale of screening because they need long time,difficult technique and high costs.Under this situation, it is urgent to create a rapid,reliable technique to diagnose DS.The purpose of this study is to establish an accurate and rapid method for diagnosis of DS.It can also be used for prenatal diagnosis of DS and benefits for degrading birth rate of DS.MethodsEight short tandem repeats(STR)in or beside Down Syndrome critical region on chromosome 21 were selected.These short tandem repeats(D21S1411,D21S1413,D21S1414,D21S1432,D21S1437,D21S1446,D21S1270,D21S2054)were high heterozygosy and the quick molecular analysis of DS was based on polymerase chain reaction and single strand conformation polymorphism.Ninty-seven periphery anticoagulated blood from 97 none relative individuals were collected and all of them were suspect of chromosome disease.The genomic DNA of all samples were extracted by salt fractionation method,then the 8 locus were amplificated,and 8 percent denatured polyacrylamide gel and silver-staining were applied.All of gels were analyzed by gel image system.At the same time,all the samples were subjected to karyotype analysis.Results1,There were four kinds of banding patterns founded at each STR locus.In type one,there was one DNA electrophoresis band as a homozygote of the allelic genes.In type two,there were two bands with approximately 1:1 density as normal heterozygote of two allelic genes.In type three,there were two bands with approximately 2:1 density,which was suspect of Down syndrome.In type four, there were three bands with approximately 1:1:1 density,which was diagnosed as Down syndrome. 2,After analyzing by short tandem repeat- polymerase chain reaction,Forty patients were diagnosed Down syndrome among 97 individuals.The results were in coincident with karyotype analysis.3,Heterozygosis of all 8 locus were found up 75%after statistical analysis.The polymorphism information content were up 50%.Conclusion1,In this study,eight short tandem repeats locus on chromosome 21 were selected and analyzed.All of them were consistent with Hardy- Weinberg law of equilibrium and were satisfied as genetic markers.Typical trisomy bands were found in each locus.2,The short tandem repeats- polymerase chain reaction method could diagnose Down Syndrome with types of classics and interchange.Comparing with karyotype analysis,the accurate rate was nearly 100%.However,it was difficulty to diagnose the mosaic when the proportion below30%.3,In a ward,this method is convenient and rapid because it does not need cell culture and the procedure is simple.It will be valuable in clinical application.