Application of combined fluorescence in situ hybridization and karyotype analysis for the diagnosis of Robertsonian translocation type trisomy 21

Objective 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. Methods 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. Results 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） （ql0;ql0） karyotype, whilst another had trisomy 21 by FISH, which has a 46, XY, rob （14;21） （ql0;ql0） karyotype. For the remaining three samples, analysis of parental peripheral blood cells indicated that their karyotypes were 45, XX, rob （ 14 ; 21 ） （ql 0 ; q l 0）, 45, XX, rob （ 15 ; 21 ） （q10 ; q 10） and 45, XX,rob（21;22） （ql0;ql0）, whilst the karyotypes of amniotic fluid cells were 46,XX, rob（14;21）（q10; q10）,46,XY,rob（15;21）（q10;q10） and46,XX,rob（21;22）（q10;q10）,respectively. Conclusion Combined FISH and chromosomal analysis is an efficient method to detect non-homologous Robertsonian translocation type trisomy 21. However, FISH has limited ability to detect homologous Robertsonian translocation type trisomy 21. Key words: Robertsonian translocations;  Trisomy 21;  fluorescence in situ hybridization;  Chromosomal karyotype