Application Of PCR-STR Quantitative Analysis In Diagnosis And Etiological Research Of Down Syndrome

Objective: Down syndrome (DS) is the most common congenitalchromosome aneuploidies and its incidence reaches to 0.13‰at present, the incidence of DS remains in high level every year in China, which giveheavy burden for family and country. Under this situation, it is urgent tocreate a rapid, reliable technique to diagnosis of DS and non-invasiveprenatal diagnosis of DS.Short tandem repeats (STR) are DNA sequences with lengthpolymorphisms in human genome which were discovered recently. Thecore sequence which consists of 2～6 base pairs is lined up repeatedly inlength, the number of repeat is 15～30 times and the lengthpolymorphisms are caused by the variety of copy in core sequence.Generally speaking there is a STR locus between 6～10kb. STR locidistribute extensively and have higher information, polymorphism, and its heredity is based on Mondel codominant inheritance. We usehalf-quantitative analysis of STR polymorphism loci, to set up a clinicalpractical method that is highly accurate in rapidly detecting and prenatalgene diagnosing Down syndrome.Materials and Methods: Four short tandem repeats loci in or nearDown syndrome critical region (DSCR) were analyzed and detected bypolymerase chain reaction and DNA half-quantitative analysis. The bloodsamples of 22 core ancestries were extracted by classic SDS-proteinK-phenol chloroform method. After four STR loci (D21S11,D21S1270,D21S1437,D21S1435)had been amplified by PCR amplification,electrophoresis on 6％denatured polyacrylamid gel, the gel was fixed,silver-dyed and coloured until the bands were clear. We read the bandsand distinguish individual genotype through the quantitative analysis.Results: There were four types by DNA half-quantitative analysis todifferent individual at a STR locus. In type one, a homozygote of oneallelic gene was detected. In type two, a normal heterozygote of twoallelic genes was found, the content of two DNA electrophoresis bandswas approximately 1:1. In type three, a Down syndrome patient of twoallelic genes was discovered. The quantity of two electrophoresis bandswas nearly 2:1. In type four, the patient showed three DNAelectrophoresis bands of which content was approximately 1:1:1. 2,Nomutation was detected in 44 meiosis for the four STR loci. Family analysis of the STR loci confirmed their Mendelian inheritance model. 3,In 22 core ancestries, the parental origin of the extra chromosome 21was determined in 21 Down syndrome out of 18 core ancestries, with 14and 4 inherited from mother and father respectively.Conclusion: 1,A rapid gene diagnosis for Down syndrome can be usedfor half-quantitative analysis of STR polymorphism loci, which is helpfulfor prenatal diagnosis. 2,The parental origin of the extra chromosome 21can be detected in most Down syndrome using these four loci, and thisexperiment is helpful to illustrate the mechanism of chromosomenondisjuncion. Moreover, the operation is simple and rapid. To sum up,the method can be used clinically and it is useful to etiological research ofDown syndrome.