| Objective To set up a clinical practical method that is highly accurate in rapidly detecting and prenatal diagnosing Down syndrome.Methods The six short tandem repeat (STR) loci onchromosome 21 of 10 families of Down syndrome were detected by polymerase chain reaction-simple sequence length polymorphism (PCR-SSLP). Besides, 4 fetuses were prenatal diagnosed with this method.Results (1) 10 individuals of Down syndrome were diagnosed by PCR-SSLP, the result of which was consistent with that of cytogenetic analysis. (2) The electrophoretic results of 60 STR loci in total of 10 individuals of Down syndrome were analyzed . 30 percent (18 of 60) of them demonstrated a triallelic pattern of three DNA bands, and their ratios of density were 1:1:1; 51.7 percent (31 of 60) displayed a diallelic pattern of two DNA band with ratios of 2:1. (3) The observed heterozygosities of D21S16, D21S11, D21S1432, D21S1437, D21S1270 and D21S1446 were 0.75, 0.70,0.65, 0.75, 0.70 and 0.85 respectively. (4) No mutation was detected in 20 meiosis for the six STR loci. Family analysis of the STR loci confirmed their Mendelian inheritance model. (5) The parental origin of the additional chromosome 21 in 10 individuals with Down syndrome were detected. 9 of them inherited from mother, of which 77.8 percent occurred in meiosis I and 22.2 percent occurred in meiosis II . 1 of them inherited from paternal meiosis I . (6) Two fetuses with Down syndrome were prenatal detected among 4 high-risk fetuses. The results were concordant with karyotyping performed by conventional cytogenetics in all cases. Conclusions The six STR loci specific for chromosome 21 were highly polymorphic, and consistent with Mendelian inheritance model. It is completely accuracy to detect and prenatal detect typical Down syndrome and translocation type of Down syndrome by PCR-SSLP of the six STR loci. Moreover, the operation was simple and rapid. To sum up, the method can be used clinically and it is helpful to etiological research of Down syndrome. |
