| Down syndrome(DS) is the most common congenital chromosome aneuploidies and its incidence reaches to 0.12%. At present, the diagnosis of DS mainly depends on cytogenetic analysis through amniocentesis, chorionic villus sampling or puncture of umbilical vein to recovery fetal cell. There are a few drawbacks: Firstly, the amniocyte culture is quite difficult and it cost more than two weeks to complete. So the prenatal diagnosis of DS is not easily to perform in many hospitals, especially in country hospital. Secondly, those inspection techniques are belong to invasive manipulation which may lead to 1% fetus abortioa So many pregnant women with high risk of DS refuse to accept those inspection. Owing to the above deficiency, the incidence of DS remains in high level every year in China, which give heavy burden for family and country. Under this situation, it is urgent to create a rapid, reliable technique to diagnosis of DS and non-invasive prenatal diagnosis of DS.Short tandem repeats (STR) exists in widespread genome and easily carry out to judge STR marker. STR marker shows normal diallelic pattern with a ratio of 1:1 or homozygous in normal human beings. Trisomic triallelic pattern is a "Gold standard" for diagnosis of DS and trisomic diallelic pattern with a ratio of 2:1 also is a powerful indicator for DS. Therefore, we can use of DNA polymorphism to diagnosis of DS if we chose some STR loci in or near to DS critical region on chromosome 21. Because different nations have different distribution structures of STR marker, it is premise to elucidate local people's structure of STR loci before genetic diagnosis. More than 200 people without relationship were carried out randomly to elucidate the structure of nine loci of D21S1432, D21S1413, D21S1414, D21S1446, D21S1437, D21S2039, D21S1270, D21S1411 and 21S1412 in Chinese Han population in Beijing. According to sequence of STR loci provided by genebank in MEDLINE, we design nine pair of primers to perform PCR and judge genetypes using polyacrylamide gel electrophoresis and silver staining or automated fluorescent laser activated detection sequencer.The statistical result using SPSS software is in agreement with Haidy-Weinberg equatioa Those 9 STR loci were verified as good genetic markers with high heterozygosity and polymorphism information contents and also provide date for paternity identification.23 suspects of DS and 26 cases of fetal amniocytes come from pregnant woman with high risk of DS were undertook to analysis 10 STR loci simultaneously by PAGE and silver staining or automated fluorescent laser activated detector sequencer(ABI310). 6 suspects of DS were determined as DS by trisomic triallelic with a ratio of 1:1:1 and the other STR loci show normal diallelic pattern with a ratio of 1:1 or homozygous with two alldes of the same size. The other one suspect determined as DS by 7 STR marker showing trisomic diallelic band or peak. The results of genetic diagnosis were identical to cytogenetic analysis which cost more than two weeks to complete. But it just cost within 2 days to complete the genetic diagnosis. Therefore, genetic diagnosis of DS is a rapid and reliable techniques and it promote development of prenatal diagnosis of DS. But it is risk to carry out gene diagnosis just depended on one or two STR loci. Quantitative fluorescent PCR was used to detect triallellic peaks or trisomic diallelic peaks to diagnosis DS depended on 1 to 4 STR loci. We also established a quantitative fluorescent PCR method to detect triallelic peaks in almost 100% DS depended on 10 STR loci.In the past few year fetal cells were discovered in maternal blood and then non-invasive prenatal diagnosis was paid more attention. The total nucleated cells were collected by gradient centrifuge from peripheral blood, and then nucleated red blood cells were enriched from the total nucleated cell by magnetic activated cell sorting. The fetal erythrocytes were identified by Kleihauer test and microdissected on slide under micromanipulation. From the single fetal erythrocyt...
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