Routine cytogenetic analysis provides important information on diagnostic and prognostic relevance for hematological malignancies. However, it is often difficult to obtain good karyotypes, especially of cells from cases with acute lymphoblastic leukemia (ALL) because of poor morphology and spreading. Thus, detailed karyotyping can be hampered and even in case of a ‘normal karyotype’ according to banding cytogenetics doubts remain if the result is reliable. In order to address this problem a series of 37 ALL cases without any detectable numerical or structural chromosomal defects was selected and studied by two recently developed multicolor fluorescence in situ hybridization (FISH) approaches: 1) multitude multicolor banding (mMCB) is a FISH-banding technique, which allows the analyses of inter- and intra-chromosomal rearrangements of the whole human karyotype in one single experiment; 2) chromosome-specific subcentromere/subtelomere-specific multicolor (subCTM-)FISH applies locus-specific subtelomeric and subcentromic probes and enables the characterization of the subtelomeric and peri-centric regions of the chromosomes, not analyzable by other FISH-approaches. Thus, we detected the following recurrent cryptic chromosomal aberrations: del(12)(pter) [8 cases], del(9)(qter) [3 cases], and del(11)(pter) [2 cases]. Moreover, cryptic changes in additional nine subtelomeric and in two subcentromeric regions were observed one time, each. In summary, mMCB and subCTM were proven to be powerful methods in the screening for new cryptic chromosomal aberrations, which considerably increased the accuracy of cytogenetic diagnosis.

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