Chromosomal rearrangements detected by FISH and G-banding.

Fluorescence in situ hybridization (FISH) using chromosome-specific DNA libraries as painting probes, locus-specific unique sequence (cosmid) probes, and Y-specific repetitive sequences was applied in the analysis of eighteen cases of chromosomal rearrangements of undetermined nature. FISH clarified the origin of the extra or translocated chromosome segments in seventeen patients, one with 2q+, two with 4q+, one each with 6p+, 7p+, 9q+, 10p+, 11q+ and 12p+, two with 13q+, and one each with 15q+, 17p+, 18p+, 20p+, 21p+ and Yq+, as well as the nature of a de novo supernumerary chromosome marker in a previously reported case. By G-banding and molecular cytogenetic studies of the family members, six cases were determined to have unbalanced translocations inherited from the carrier parent. The extra translocated genetic material may cause specific trisomic syndromes, including partial 6p21.3-p23, 9q32-q34.3, 13q32-q34, 15q24-q26, and 17p11.2-p13 trisomies in those patients. A translocated 21q segment on 12p was shown by a painting probe in a patient with Down features. A patient with cat cry syndrome resulting from a loss of the terminal segment of the short arm of chromosome 5 was confirmed by a cosmid probe showing de novo reciprocal translocation between chromosomes 5 and 18:t(5;18) (p13.3;p11.31). With FISH, the extra material on the rearranged chromosome could also be identified as duplicated or translocated. The FISH technique thus provides a method for the analysis of extra structurally abnormal chromosomes (especially in de novo cases), recognizable syndromes (contiguous gene syndromes) caused by translocated deletion from parental balanced chromosome rearrangements, and supernumerary marker chromosomes. FISH subsequent to G-banding is also of great help in the confirmation of preliminary abnormal G-banded karyotypes after a modified destaining procedure. In conclusion, the combination of G-banding and FISH is very useful in the accurate diagnosis of chromosomal rearrangements.