Detection of trisomy 21 by quantitative fluorescent-polymerase chain reaction in uncultured amniocytes

A comparative analysis of the effectiveness of cytogenetic and molecular genetic methods in the detection of Down syndrome

The goal of this study was to examine the effectiveness of 6 STR markers application (D21S1435, D21S11, D21S1270, D21S1411, D21S226 and IFNAR) in molecular genetic diagnostics of Down syndrome (DS) and to compare it with cytogenetic method. Testing was performed on 73 children, with the previously cytogenetically confirmed Down syndrome. DNA isolated from the buccal swab was used. Previously mentioned loci located on chromosome 21 were simultaneously amplified using quantitative fluorescence PCR (QF PCR). Using this method, 60 previously cytogenetically diagnosed DS with standard type of trisomy 21 were confirmed. Furthermore, six of eight children with mosaic type of DS were detected. Two false negative results for mosaic type of DS were obtained. Finally, five children with the translocation type of Down syndrome were also confirmed with this molecular test. In conclusion, molecular genetic analysis of STR loci is fast, cheap and simple method that could be used in detection of DS. Regarding possible false results detected for certain number of mosaic types, cytogenetic analysis should be used as a confirmatory test.

Preimplantation genetic diagnosis for Down syndrome pregnancy

OBJECTIVE

To evaluate the effect of preimplantation genetic diagnosis (PGD) conducted for women who had Down syndrome pregnancy previously.

METHODS

Trisomy 21 was diagnosed by using fluorescence in site hybridization (FISH) before embryo transfer in two women who had Down syndrome pregnancies. Each received one or two PGD cycles respectively.

RESULTS

Case 1: one PGD cycle was conducted, two oocytes were fertilized and biopsied. One embryo is of trisomy 21 and the other of monosomy 21. No embryo was transferred. Case 2: two PGD cycles were conducted, in total, sixteen oocytes were fertilized and biopsied. Four embryos were tested to be normal, six of trisomy 21, and one of monosomy 21. Five had no signal. Four normal embryos were transferred but no pregnancy resulted.

CONCLUSION

For couples who had pregnancies with Down syndrome previously, PGD can be considered, and has been shown to be an effective strategy.

Practical application of fluorescent quantitative PCR on Trisomy 21 in Chinese Han population

OBJECTIVE

To apply the fluorescent quantitative PCR method on the detection of Trisomy 21 by D21S11 locus and make a foundation for rapid prenatal diagnosis of Trisomy 21.

METHODS

About 409 controls (39 amniotic fluid samples and 370 peripheral blood samples) and 35 patients (4 amniotic fluid samples and 31 peripheral blood samples) with Trisomy 21 were tested using fluorescent quantitative PCR by amplification of DNA fragment on D21S11 STR locus. The results were compared with conventional cytogenetic analysis to confirm the utility of this method. And the allele frequency distributions of D21S11 STR locus were analyzed.

RESULTS

The 95% reference interval of fluorescent intensity ratios of peak heights of PCR products amplified from two alleles on D21S11 locus ranged from 0.84 to 1.42 (1.13 +/- 0.29) in heterozygous controls. About 19 out of 35 patients showed a "diallelic" pattern and their height ratio of fluorescent peaks of PCR products amplified from two alleles in patients with "diallelic" patterns were all outside of the 95% reference range of controls. The PCR products of DNA from 12 patients presented the third allele. No sample with the "monoallelic" pattern was found. Four chimeras diagnosed by cytogenetic method could not be diagnosed by this method. There were 17 and 11 alleles found in controls and patients, respectively. About 343 out of 409 controls were heterozygous and the heterozygosity was 83.86%. We did not find any significant differences in the frequency distributions of alleles on D21S11 locus between controls and patients. But there were significant differences in the frequency distributions of alleles on D21S11 locus between controls and patients. But there were significant differences in the frequency distributions of alleles on D21S11 locus among different populations.

CONCLUSIONS

The fluorescent quantitative polymerase chain reaction method was rapid, accurate, and only small amount of starting material was needed, it could be applied in rapid prenatal diagnosis of Trisomy 21. D21S11 was a good marker with high heterozygosity for the screening of Trisomy 21. And the frequency distributions of alleles on D21S11 locus were significantly related to ethnic background.