Translocation trisomy dup(21q) and free trisomy 21 can be distinguished by interphase-FISH

• Published in: International journal of molecular medicine Vol. 3; no. 1; p. 11
• Main Authors: Liehr, T, Starke, H, Beensen, V, Kähler, C, Harbich, M, Brude, E, Ziegler, M, Claussen, U
• Format: Journal Article
• Language: English
• Published: Greece 01-01-1999
• Subjects: Amniotic Fluid - cytology; Cell Nucleus - metabolism; Chromosomes, Human, Pair 21 - genetics; DNA Probes; Female; Fetal Diseases - diagnosis; Fetal Diseases - genetics; Humans; In Situ Hybridization, Fluorescence; Interphase; Pregnancy; Prenatal Diagnosis; Translocation, Genetic; Trisomy - diagnosis; Trisomy - genetics
• ISSN: 1107-3756
• DOI: 10.3892/ijmm.3.1.11

The possibility of distinguishing in routine diagnostics translocation trisomy dup(21q) from disomy 21 as well as from free trisomy 21 using interphase fluorescence in situ hybridization (FISH) with a single copy probe (LSI 21) localized on chromosome 21q22.13-q22.2 is described. In free trisomy 21 and translocation trisomy dup(21q) 94%-98% of the nuclei exhibit 3 specific signals, while in disomy 21 only up to 6% of them have 3 false positive signals. Furthermore, reliable differentiation between free and translocation trisomy dup(21q) can be achieved by evaluating the percentage of nuclei with one single and two co-localized chromosome 21q22.13-q22.2 specific signals in 50-100 interphase nuclei. While in translocation trisomy 75+/-4.3% are co-localized due to a chromosomal rearrangement, in free trisomy 21 only 40+/-2.83% of the nuclei have two co-localized signals by chance. No differences in interphase signal distribution could be detected in two cases with a dicentric chromosome dup(21q) compared to one case with a monocentric one, a comparison not previously carried out. In addition, the single copy probe LSI 21 was compared with the alphoid probe D13Z1/D21Z1 which was found to be unsuitable for such assays due to polymorphisms in the á satellite regions of chromosome 21.