Figure 1.

Cytogenetic detection of chromosomal aberrations. (A) R-banding, based on the morphological criteria of chromosomes, was the first and widely used technique for clinical cytogenetics. The detection of clonal aberration t (9;10)(q34;q2?6) in a renal-tract malformation patient without information on the precise breakpoint of chromosome 10 or the nature of translocation (balanced or unbalanced). (B) Telomere (red) and centromere (green) staining allows reliable classification of chromosomes and identification of chromosomal aberrations, such as t(9;10)(q34;q26.3), with precise localization of breakpoints confirming the reciprocal translocation. This particular reciprocal translocation involved the telomere region of chromosome 10. (C) The precise detection of the centromeric regions identifies all chromosomal aberrations, including dicentric chromosomes, in particular when both centromeres are very close, such as a tric (red arrow). The M-FISH technique does not stain the centromeric region. Telomere and Centromere staining followed by M-FISH technique (TC+M-FISH ) permits the reliable scoring and identification of all chromosomal aberrations, such as the dic (12;17), which could be mistaken for two chromosomes using only M-FISH. (D) Detection of a centric ring in circulating lymphocytes of a patient with a genetic syndrome using TC staining (c). This centric ring was undetectable by R-Banding(a) or M-FISH (b).