RESUMEN
<p><b>OBJECTIVE</b>To assess the value of fluorescence in situ hybridization (FISH) combined with chromosomal analysis for the detection of Robertsonian translocation type trisomy 21 in amniotic fluid cells.</p><p><b>METHODS</b>Amniotic fluid samples from pregnant women requesting prenatal diagnosis were cultivated. Metaphase cells were prepared for G-banding karyotype analysis. For the 5 Robertsonian translocation type trisomy 21, interphase nuclei from amniotic fluid and parental peripheral blood cells were prepared for FISH analysis.</p><p><b>RESULTS</b>In 2 cases, analysis of parental peripheral blood cells showed normal karyotypes. FISH analysis of amniotic fluid cells indicated that one sample had two copies of chromosome 21, which has a 46, XY, rob(21;21)(q10;q10) karyotype, whilst another had trisomy 21 by FISH, which has a 46, XY, rob(14;21)(q10;q10) karyotype. For the remaining three samples, analysis of parental peripheral blood cells indicated that their karyotypes were 45, XX, rob(14;21)(q10;q10), 45, XX, rob(15;21)(q10;q10) and 45, XX, rob(21;22)(q10;q10), whilst the karyotypes of amniotic fluid cells were 46, XX, rob(14;21)(q10;q10), 46, XY, rob(15;21)(q10;q10) and 46, XX, rob(21;22)(q10;q10), respectively.</p><p><b>CONCLUSION</b>Combined FISH and chromosomal analysis is an efficient method for detecting non-homologous Robertsonian translocation type trisomy 21. However, FISH has limited ability to detect homologous Robertsonian translocation type trisomy 21.</p>