High rates of submicroscopic aberrations in karyotypically normal acute lymphoblastic leukemia.

BACKGROUND: Acute lymphoblastic leukemia (ALL) is not a single uniform disease. It consists of several subgroups with different cytogenetic and molecular genetic aberrations, clinical presentations and outcomes. Banding cytogenetics plays a pivotal role in the detection of recurrent chromosomal rearrangements and is the starting point of genetic analysis in ALL, still. Nowadays, molecular (cyto)genetic tools provide substantially to identify previously non-detectable, so-called cryptic chromosomal aberrations in ALL. However, ALL according to banding cytogenetics with normal karyotype - in short cytogenetically normal ALL (CN-ALL) - represent up to ~50 % of all new diagnosed ALL cases. The overall goal of this study was to identify and characterize the rate of cryptic alterations in CN-ALL and to rule out if one single routine approach may be sufficient to detect most of the cryptic alterations present. RESULTS: Sixty-one ALL patients with CN-ALL were introduced in this study. All of them underwent high resolution fluorescence in situ hybridization (FISH) analysis. Also DNA could be extracted from 34 ALL samples. These DNA-samples were studied using a commercially available MLPA (multiplex ligation-dependent probe amplification) probe set directed against 37 loci in hematological malignancies and/or array-comparative genomic hybridization (aCGH). Chromosomal aberrations were detected in 21 of 61 samples (~34 %) applying FISH approaches: structural abnormalities were present in 15 cases and even numerical ones were identified in 6 cases. Applying molecular approaches copy number alterations (CNAs) were detected in 27/34 samples. Overall, 126 CNAs were identified and only 34 of them were detectable by MLPA (~27 %). Loss of CNs was identified in ~80 % while gain of CNs was present in ~20 % of the 126 CNAs. A maximum of 13 aberrations was detected per case; however, only one aberration per case was found in 8 of all in detail studied 34 cases. Of special interest among the detected CNAs are the following new findings: del(15)(q26.1q26.1) including CHD2 gene was found in 20 % of the studied ALL cases, dup(18)(q21.2q21.2) with the DCC gene was present in 9 % of the cases, and the CDK6 gene in 7q21.2 was deleted in 12 % of the here in detail studied ALL cases. CONCLUSIONS: In conclusion, high resolution molecular cytogenetic tools and molecular approaches like MLPA and aCGH need to be combined in a cost-efficient way, to identify disease and progression causing alterations in ALL, as majority of them are cryptic in banding cytogenetic analyses.

BAC-probes applied for characterization of fragile sites (FS).

Genomic instability tends to occur at specific genomic regions known as common fragile sites (FS). FS are evolutionarily conserved and generally involve late replicating regions with AT-rich sequences. The possible correlation between some FS and cancer-related breakpoints emphasizes on the importance of understanding the mechanisms of chromosomal instability at these sites. Although about 230 FS have already been mapped cytogenetically, only a few of them have been characterized on a molecular level. In this chapter, we provide a protocol for mapping of common FS using bacterial artificial chromosome (BAC) probes in fluorescence in situ hybridization (FISH) and suggest the usage of lymphocytes from Fanconi anemia patients as a model system. In the latter, rare FS are expressed much more frequently than in, for example, aphidicolin-induced blood lymphocyte preparations. Knowing the exact location of FS enables the molecular comparison of their location and breakpoints that appear during evolution, cancer development and inherited disorders.

MLLT10 and IL3 rearrangement together with a complex four-way translocation and trisomy 4 in a patient with early T-cell precursor acute lymphoblastic leukemia: A case report.

Cytogenetic classification of acute lymphoblastic leukemia (ALL) is primarily based on numerical and structural chromosomal abnormalities. In T-cell ALL (T-ALL), chromosomal rearrangements are identified in up to 70% of the patients while the remaining patients show a normal karyotype. In the present study, a 16-year-old male was diagnosed with T-precursor cell ALL and a normal karyotype after standard GTG-banding, was studied retrospectively (>10 years after diagnosis) in frame of a research project by molecular approaches. In addition to molecular cytogenetics, multiplex ligation-dependent probe amplification (MLPA) and high resolution array-comparative genomic hybridization (aCGH) were also applied. Thus, the following yet unrecognized balanced chromosomal aberrations were detected: der(3)t(3;5)(p23;q31.1), der(5)t(3;5)(p23;q35.3), der(5)t(5;10)(q31.1;p12.3) and der(10)t(5;10)(q35.3;p12.3). The oncogene MLLT10 was involved in this rearrangement as was the IL3 gene; in addition, trisomy 4 was present. All of these clonal aberrations were found in 40% of the cells. Even if this complex karyotype would have been identified at the time of diagnosis, most likely no other protocol of anticancer therapy (ALL-BFM 95) would have been applied. Three months after the end of a successful 2-year treatment, the patient suffered from isolated bone marrow relapse and died of sepsis during ALL-REZ-BFM protocol treatment.

Global screening and extended nomenclature for 230 aphidicolin-inducible fragile sites, including 61 yet unreported ones.

Since the first description of human fragile sites (FS) more than 40 years ago, a variety of substances were reported to induce chromosomal breaks at non-random, breakage-prone regions. According to information available from human genome browsers aphidicolin, an inhibitor of DNA replication induces 77 of 88 known common FS. However, in the literature additional FS are reported, which are also, at least in part, inducible by aphidicolin. To the best of our knowledge, here we present the first and largest ever done systematic, whole genome-directed and comprehensive screening for aphidicolin-inducible breakage-prone regions. The study was performed on stimulated peripheral blood lymphocytes of 3 unrelated healthy individuals. Twenty-five thousand metaphase spreads were analyzed and overall 22,537 FS located in 230 different loci were recorded. Sixty-one of those FS were never observed before and 52 were already previously reported but not included in genome browsers and yet verified. Interestingly, aphidicolin was able to induce all types of rare and common FS, suggesting that these breakage-prone regions are less dependent on the inducing chemicals than originally supposed. Overall, we provide the first comprehensive genome wide map for FS and studied possible correlations of chromosome length and GTG-banding level with FS-frequency. To handle FS better in future, an extension of the already existing alphabetical nomenclature for FS on single chromosomes is suggested.

New aspects on chromosomal instability: chromosomal break-points in Fanconi anemia patients co-localize on the molecular level with fragile sites.

Within cytogenetic preparations chromosomal breaks can be observed in patients suffering from Fanconi anemia (FA), a recessively inherited syndrome with an extremely elevated cancer risk, but also in healthy individuals as so-called fragile sites (FS). It is known that FS cytogenetically co-localize with tumor- and evolutionary-conserved chromosomal break-points. The also suggested co-localization of FS and FA associated break-points (FA-bp) was studied here for the first time systematically by molecular cytogenetics. Metaphase chromosomes were obtained from lymphocytes of two FA patients (FANC-A and FANC-C, respectively). Overall 50.58% of the investigated FA-bp correspond to cytogenetic regions with known FS. A detailed molecular cytogenetic study applying FS-spanning probes revealed that 24/29 (82.8%) of analyzed FS are in concordance with FA-bp. Notably, FA-bp show a distribution pattern deviating from that of Aphidicolin induced FS. FA-bp appear more frequently within GTG-light bands and additionally, a yet unreported correlation was observed between break rate and chromosomal banding level. In future, FA-bp might serve as model for the mapping and analysis of otherwise rarely observable FS.