Purpose: In situ hybridization (ISH) is an efficient tool for detecting chromosomal abnormalities in haemopoietic malignancies. Structural and numerical changes typical of most pathological entities can be detected using chromosome-specific probes on interphase or metaphase cells by means of this technique.
Patients and methods: In this report we present chromosome analysis combining conventional cytogenetics with ISH in 121 patients affected with different haematological diseases. We have studied 92 patients with B-chronic lymphoproliferative disorders (B-CLPD), 11 myelodysplastic syndromes (MDS), 17 acute nonlymphocytic leukaemias (ANLL), 1 acute lymphocytic leukaemia and 1 aplastic anaemia. The ISH was carried out with two kind of biotin-labeled probes: a) 8 and 12 centromeric alpha satellite probes and b) whole painting chromosome (WPC) library probes from all the chromosomes except numbers 10, 16, 21, X and Y.
Results: The cytogenetic analysis of B-CLPD has been hampered by several problems. These leukaemic cells have very low spontaneous mitotic activity and the cell response to mitogens is often poor, unpredictable and variable. Even so, an extra chromosome 12 (+ 12) is one of the most frequent abnormal karyotypes reported. ISH and chromosome 12 specific biotinylated alpha satellite DNA probe was applied in 84 patients with B-CLPD. Among 50 patients with typical chronic lymphocytic leukaemia (CLL) the ISH studies showed two signals of hybridization in the 50 cases. By conventional cytogenetics 9 out of 18 atypical CLL showed chromosomal abnormalities and 7 of them trisomy 12. ISH detected trisomy 12 in 11 of these cases. Trisomy 8 is the most frequent karyotypic change in MDS and ANLL. Cytogenetic results revealed a clear extra copy of chromosome 8 in 13 cases. In all of these trisomic cases, the presence of trisomy 8 clone was confirmed by ISH. ISH revealed trisomy 8 not detected by conventional cytogenetics in 7 cases. The yield of trisomy is much higher with the ISH technique than with conventional cytogenetics. Finally, conventional cytogenetics combined with CISS (chromosomal in situ suppression) hybridization was performed in 15 patients affected with different haematological diseases showing structural aberrations, complex karyotypes or marker chromosomes.
Conclusions: Our results show that ISH can detect both numerical and structural chromosome changes with high specificity and reliability. The fact that chromosome spreads of very poor quality can now be included in such analysis is the decisive advantage of this approach.