Application of real-time PCR in prenatal diagnosis of Down's syndrome

Chong school, fight career, modern people get married late and late!

With the development of society, the extension of the years of education for modern people, coupled with the transformation of modern marriage concepts and women's independent consciousness, makes modern people get married one night later. According to the survey, the average age of first marriage in Beijing reached 27 years old, which was nearly one year older than three years ago, and late marriage will inevitably bring about late childbearing.

A woman who is 34 years old at the age of pregnancy and who is 35 years old at the time of production can be called a senior woman. Older women not only have a high risk during pregnancy, but with the increase of age, the egg is prone to the best "shelf life", resulting in problems such as decreased quality and high probability of chromosome abnormality during fertilization, resulting in increased fetal teratogenicity. Down's syndrome, 21 -trisomy syndrome, also known as congenital or Down syndrome ( DS ), is a disease caused by chromosomal abnormalities (an extra chromosome 21 ), 60% of children in the fetus Early abortion, survivors have obvious intelligence behind, special face, growth and development disorders and multiple deformities. . Down sick children and increase in the incidence increases with maternal age, maternal age at 35 years of age, the incidence rate of 1/300 children, 40 to 45 years old is more than 1/100, 1/50 45 years old.

There are about 20,000 children with Down syndrome born in China every year. There is no effective cure method for this disease, which has caused a great economic burden for the family and society. Therefore, prenatal diagnosis of Down's syndrome is done. , with significant economic and social value.

At present, the gold standard for prenatal diagnosis of DS in China is karyotype analysis method, but its operation is cumbersome and the test period is long (different hospitals, some need about one month), and the dependence on technicians' karyotype analysis ability is large. Fluorescence in situ hybridization (FISH) detection of DS children is rapid, but the price is higher, and the experimental factors have more factors. Whole genome copy number analysis can analyze genome-wide copy number variation, but the method relies on company chips and large-scale analysis equipment. The cost is high, the operation is complicated, the amount of data is so large that the analysis is relatively complicated, and the chimeric and heterogeneous cannot be detected. Bit type DS.

In addition to the above methods, cytogenetics and molecular genetics scholars are studying the use of multiple QS-PCR methods for prenatal diagnosis of Down's syndrome. Multiple QF-PCR amplifications were performed on multiple short tandem repeat (STR) sites on chromosome 21, PCR products were subjected to capillary electrophoresis, and STR DNA was polymorphized using GeneMapper software, and each STR locus was detected. A 1: 1: 1 isocratic peak or a 2: 1 (or 1: 2) peak is the triploid of the corresponding chromosome, which is DS positive. At the same time, lymphocyte culture and karyotype analysis were performed on the peripheral blood of the children. The results of multiple QS-PCR methods and karyotype analysis were basically the same.

The use of multiple QF-PCR to detect the cost of children with DS is greatly reduced, accurate and fast (one day results, reduce the anxiety of patients waiting for anxiety), high-throughput detection, objective interpretation criteria, not only for cord blood, but also for Rapid detection of fetal exfoliated cells and villus tissue in amniotic fluid. Combined with karyotype analysis, it plays an effective complementary role and has high clinical application and promotion value.

It is worth noting that some studies have shown that the positive rate of single STR detection is 17% to 83%, and the positive detection rate of the four STR combinations is 100%. Therefore, the number of selected STR loci and their genetic efficacy, mutation probability, etc. Directly affect the accuracy of the results. In addition, the chimeric sample has a chimeric ratio (most scholars believe that QF-PCR can generally detect a chimeric ratio of more than 10% of the chimera), and it will also affect the effect of amplification, which may lead to missed detection.

Therefore, the application of QF-PCR method in prenatal diagnosis to avoid false positives and missed examinations requires further research and discussion. It is recommended to establish standardized processes and standards for early entry into clinical applications.

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