Study On Prenatal Molecular Diagnosis Of Down's Syndrome

Objective To investigate the feasibility of PCR amplification of two STR loci D2IS 1411 and D21S1413 in or near the Down syndrome critical region located on chromosome 21 for molecular diagnosis and prenatal molecular diagnosis of Down's syndrome. The aim of the study was to develop a stable, accurate, simple and rapid gene diagnosis technique for Down's syndrome in clinic.Methods 100 blood samples from unrelated individuals of Han nationality in Tianjin areas were collected. A multiplex PCR involving D21S1411 and D21S1413 loci was used. Non-degeneration polyacrlamide gel electrophoresis and silver staining were performed to detect the amplification products. 34 Down's syndrome patients who had been diagnosed by cytogenetic analysis were detected using this technique. The Down's syndrome was identified by the number of alleles: 3 alleles bands whose density was same, 2 alleles bands with one obvious higher density compared to the other. 65 amniotic fluid samples and 60 chorionic villus samples were analyzed simultaneously using this method and the results were compared with the cytogenetic analysis.Results A multiplex PCR system of two STR loci had been established. In normal individuals, two allelic distribution pattern were noticed: 2 alleles bands of 1:1 for heterozygous or 1 band for homozygous. The heterozygosity of D21S 1411 locus was 64% and the heterozygosity of D21S1413 locus was 66%. In 34 Down's syndromepatients, 1 patients showed 3 alleles bands of 1:1:1, 18 patients showed 2 alleles bands of 2:1, 15 patients showed 1 band in D21S1411 locus. 55.9% Down's syndrome patients had been diagnosed. 6 patients showed 3 alleles bands of 1:1:1, 19 patients showed 2 alleles bands of 2:1, 9 patients showed 1 band in D21S1413 locus. 73.5% patients had been diagnosed. Combined with two STR loci 85.3% (29/34) patients had been diagnosed. No samples showed 1:1 pattern. Among 65 amniotic fluid samples, 1 sample was diagnosed as Down's syndrome. D2IS 1411 locus showed 3 alleles bands of 1:1:1 and D2IS 1413 locus showed 2 alleles bands of 2:1. The results coincided with the results of cytogenetics. No patient had been detected using molecular technique among 60 chorionic villus samples, while 1 Down's syndrome patient was detected by cytogenetic analysis (45,XY,rob(21;22)/46,XY, rob(21;22),+21(41.2%)). The efficiency for prenatal molecular diagnosis of Down's syndrome was 99.2%.Conclusion 1. D21S1411 and D2IS 1413 loci had high heterozygosity in individuals of Han nationality in Tianjin areas. They were properly genetic markers on chromosome 21.2. A multiplex PCR system of two STR loci was feasible, stable and could be used for molecular diagnosis of Down's syndrome in clinic.3. The multiplex PCR system could be used for molecular diagnosis and prenatal molecular diagnosis of Down's syndrome accurately, rapidly and simplywithin 24~48h. The results were relatively accurate. This method has high clinical values.