RESUMO
<p><b>OBJECTIVE</b>To develop a rapid method for the detection of Down syndrome (DS) using dual-color competitive quantitative fluorescent polymerase chain reaction (DCC-QF-PCR), and to assess its feasibility for the prenatal diagnosis of Down syndrome.</p><p><b>METHODS</b>DNA was extracted from peripheral blood of 30 DS patients and 60 normal men, common primers for DSCR and USC2 genes and respective TaqMan probes were designed and synthesized. The results of DCC-QF-PCR were compared with those of QF-PCR which measured the ratio between DSCR and GAPDH. Forty-six amniotic fluid samples were assayed with DCC-QF-PCR. The results were compared with that of karyotyping. Monoclone fragments for DSCR and USC2 genes were obtained from direct cloning of PCR products. DCC-QF-PCR was carried out using different DNA ratios of DSCR and USC2 as the template. The dosage ratio between DSCR and USC2 was calculated.</p><p><b>RESULTS</b>The gene dosage ratio of the DS patients was 1.41-1.74, which was significantly higher than that of normal men (0.93-1.15). The dosage ratio range of DSCR and GAPDH by QF-PCR was comparatively greater than that of DSCR and USC2. Three samples were diagnosed as DS, which was in good agreement with that of karyotyping analysis. There was no significant difference between the gene dosage ratio from DCC-QF-PCR and that of predetermined (P>0.05).</p><p><b>CONCLUSION</b>DCC-QF-PCR is an accurate, rapid, and low cost method, which only requires tiny amount of sample and therefore has broad application in the genetic and prenatal diagnosis.</p>