ABSTRACT
<p><b>OBJECTIVE</b>Developing a PCR-based method to diagnose trisomy 21 directly by alternative detection of the SSCP profiles of the STR fragments amplified.</p><p><b>METHODS</b>The DNA samples from 19 trisomy 21 patients, 3 at-risk fetuses of trisomy 21 and a total of 44 samples from their parents as controls were drawn for this study, in which the trisomy 21 was determined by G-band karytyping. Two polymorphic STR at D21S11 and D21S1411 served as the gene markers, and two separate PCR-amplified primers were designed.The STR-amplicons denatured were subjected to polyacrylamide gel electrophoresis for SSCP analysis.</p><p><b>RESULTS</b>This assay can identify three STR fragments representing parents' chromosome 21 by detecting the electrophoresis separation profiles of PCR-amplified fragments. With the use of this assay, the authors analyzed the 22 cases of trisomy 21;accurate diagnoses were made except for one case in which the electrophoresis pattern at D21S11 site could not present the diagnostic information because of the homozygous state of this family. The 3 at-risk fetuses were found to be the trisomy 21 patients, followed by confirmation of the results by G-band karytyping of aborted samples.</p><p><b>CONCLUSION</b>The present PCR-STR-SSCP assay can be applied as a simple, rapid and accurate method in the prenatal diagnosis and genetic screening of trisomy 21.</p>