Study On The Gene Diagnosis And Prenatal Gene Diagnosis Of Down’s Syndrome

Objective To investigate the feasibility and practicability of gene diagnosis and prenatal gene diagnosis of Down’s syndrome by the technique of quantitative fluorescence polymerase chain reaction (QF-PCR), and the aim of the study was to develop a stable, accurate, simple and rapid technique of gene diagnosis for Down syndrome in clinic.Methods57DNA samples were extracted from the peripheral blood of individuals diagnosed as Down’s syndrome by karyotyping, and then amplified with three short tandem repeats markers specific to chromosome21, which included D21S1440, D21S11and Penta D loci, by QF-PCR. Amplification products were electrophoresed by ABI PRISM377sequencer and analysed by GeneScan3.1sofrware. Gene diagnosis was performed by analyzing the results.330samples for prenatal gene diagnosis (included282amniotic fluids and58chorionic villous) were diagnosed by the same methods, then the results werecompared with karyotyping. The frequencies of the normal samples’genotypes were tested with Hardy-Weinberg equilibrium. Using PowerStatsV12software genetical analysis was performed to conclude some data of population genetics such as the heterozygosities, the polymorphism information contents, the probabilities of discrimination power and the probabilities of exclusion, and so the cumulative data of D21S1440, D21S11and Penta D loci.Results1.57samples of Down’s syndrome were confirmed by karyotyping:41samples were diagnosed as Down’s syndrome by D21S1440locus, the positive percentage was71.9%,44samples were diagnosed by D21S11locus, the positive percentage was77.2%, and51samples were diagnosed by Penta D locus, the positive percentage was89.5%. In this study no sample was noninformative when all the loci were used.2.330samples for prenatal gene diagnosis:10samples were diagnosed as Down’s syndrome and320were identified normal. The sensitivities of QF-PCR by using D21S1440, D21S11and Penta D loci were70%,70%and90%.And the specificity of these three loci was100%. Both the sensitivity and the specificity were100%when used all the loci, and neither false-positive nor false-negtive results were observed.3. The alleles of the D21S1440, D21S11and Penta D loci were observed in the320normal samples, whose frequencies of the genotypes were in good agreement with Hardy-Weinberg equilibrium. The heterozygous percentages observed from these three loci were61.7%,74.1%,90.6%, the polymorphism information contents were0.60,0.76,0.80, the probabilities of discrimination power were0.811,0.927,0.915, and the probabilities of exclusion were0.311,0.494,0.808.4. The cumulative polymorphism information content, probability of discrimination power and probability of exclusion of D21S1440, D2S11and Penta D loci were0.98,0.999and0.933.Conclusions1. D21S1440, D2S11and Penta D loci had high heterozygosities and could be stable descended in individuals of Han nationality in Tianjin areas.They were properly genetic markers on chromosome21.2. Amplifying D21S1440, D2S11and Penta D loci with QF-PCR technique is reliable for gene diagnosis and prenatal gene diagnosis of Down’s syndrome accurately, rapidly and simply, and this method had high clinical values with its high sensibility and specificity.3. The genetic polymorphisms of D21S1440, D2S11and Penta D loci were high, and all of them were high valuable in the application of forensic medicine and population genetics.