The assessment of array comparative genomic hybridization in complex karyotype analyses.

Molecular-cytogenetic methods were used to analyse and specify complex genome rearrangements in malignant cells. Twelve samples of bone marrow cells were collected from patients with myelodysplastic syndromes (MDS). The complex karyotypes were examined by multicolour fluorescence in situ hybridization (mFISH), high-resolution multicolour banding (mBAND) and array comparative genomic hybridization (aCGH). For aCGH, DNA was isolated from fixed bone marrow cells in methanol and acetic acid and amplified by whole-genome amplification. Three samples were analysed by the oligonucleotide array NimbleGen on the basis of full service. BAC-based Haematochips (BlueGnome) were used for the other nine samples. Sensitivity and detection limits of both methods were compared. The results obtained by mFISH/mBAND were in most cases confirmed by the microarray technique. aCGH detected 43 unbalanced chromosomal changes that were also identified by classical cytogenetics and FISH. Moreover, aCGH discovered 14 additional changes. Cryptic amplifications and deletions were characterized with a resolution of 0.5 Mb. In one bone marrow sample with suspected monosomy 5 detected by conventional cytogenetic analysis, aCGH revealed a 22.3 Mb region of chromosome 5 inserted in another autosome within the complex karyotype. Amplified DNA was successfully used for aCGH in 11 out of 12 cases, improving resolution of unbalanced chromosomal aberrations. The combination of both approaches brought more detailed description of complex karyotypes and is highly recommended.

The role of telomeres and telomerase complex in haematological neoplasia: the length of telomeres as a marker of carcinogenesis and prognosis of disease.

Human telomeres (discovery of telomere structure and function has been recently awarded The Nobel Prize) consist of approximately 5-12 kb of tandem repeated sequences (TTAGGG)n and associated proteins capping chromosome ends which prevent degradation, loss of genetic information, end-to-end fusion, senescence and apoptosis. Due to the end-replication problem, telomere repeats are lost with each cell division, eventually leading to genetic instability and cellular senescence when telomeres become critically short. Stabilization of the telomeric DNA through telomerase activation, unique reverse transcriptase, or activation of the alternative mechanism of telomere maintenance is essential if the cells are to survive and proliferate indefinitely. Telomerase is expressed during early development and remains fully active in specific germline cells, but is undetectable in most normal somatic cells. High level of telomerase activity is detected in almost 90% of human tumours and immortalized cell lines. The hematopoietic compartment may develop genetic instability as a consequence of telomere erosion, resulting in aplastic anaemia (AA) and increased risk of myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML). Genetic instability associated with telomere dysfunction (i.e. short telomeres) is an early event in carcinogenesis. The molecular cytogenetic method telomere/centromere fluorescence in situ hybridization (T/C-FISH) can be used to characterize the telomere length of hematopoietic cells. This review describes recent advances in the molecular characterization of telomere system, the regulation of telomerase activity in cancer pathogenesis and shows that the telomeric length could be a potential clinical marker of hematologic neoplasia and prognosis of disease.