RESUMEN
<p><b>OBJECTIVE</b>To investigate the feasibility of genetic diagnosis of Down's syndrome (DS) using short tandem repeat (STR), and to develop a rapid and accurate method for diagnosing DS.</p><p><b>METHODS</b>Quantitative fluorescence polymerase chain reaction (QF-PCR) was used to amplify STR loci D21S11, D21S1440 and Penta D of 719 samples. Three hundred and eighty-nine samples were peripheral blood, 282 were amniotic fluid, 48 were chorionic villous samples. The products were analyzed using eleterophoresis to detect DS.</p><p><b>RESULTS</b>Among 652 samples with a normal karyotype, 635 showed 2 bands with a 1:1 ratio or a single band. The remaining 17 samples showed 3 bands, and were regarded as false positive results. For 67 DS samples, 53 showed 3 bands/peaks with a 1:1:1 ratio and 14 showed 2 bands/peaks with a 2:1 ratio. The sensitivity and specificity of STR loci D21S11, D21S1440 and Penta D were 76.12% and 98.62%, 71.64% and 98.93%, 89.55% and 99.85%, respectively. The overall sensitivity and specificity of 3 STR loci were 100% (67/67) and 97.39% (635/652), respectively.</p><p><b>CONCLUSION</b>Compared with conventional method, author's method is simpler, more stable and rapid, and can be used for large-scale prenatal screening of DS.</p>