Frequency and types of chromosomal abnormalities in acute lymphoblastic leukemia patients in Turkey

Design and methods: The aim of this study was to describe the types and frequencies of CAs in the childhood and adult ALL patients. To date, his was the largest study to date in of children with ALL in Turkey, and presented the general cytogenetic characteristics of 260 patients diagnosed as having with ALL in a 17-year period. The cytogenetic analyses were performed in the diagnosis of ALL patients.


Introduction
ALL is a malignant disorder of the bone marrow in which a lymphoid progenitor cell becomes genetically altered.
It is the most common malignancy of childhood with an annual incidence rate of 3-4 cases per 100,000 children. The disease is most common in children but can occur at any age.
Although, there are few identifi ed factors associated with an increased risk of developing ALL such as genetic, parental and environmental factors, the etiology of the disease remains largely unknown [1,2]. Prognostic impact of CAs in ALL patients is complex. The disease has a bimodal distribution: a sharp peak in incidence among children aged 2-5 years [3]. ALL results from somatic mutation in a single lymphoid progenitor cell at one of several discrete stages of development.  [4]. Several numerical and structural CAs are associated with childhood leukemia. The clonal origin of ALL has been established by cytogenetic analysis. Numerous genetic alterations have been and continue to be discovered in ALL, and it has been repeatedly shown that specifi c genetic abnormalities are present in the majority of successfully karyotyped patients with ALL [5][6][7]. Anoplidy is seen in 30-40% of all cases of Arch Community Med Public Health 5(2): 055-061. DOI: http://dx.doi.org/10.17352/2455-5479.000055 childhood ALL. Numeric chromosomal changes are usually encountered in chromosomes 4,6,8,10,14,17,18,20 and 21 [8][9][10][11]. Recurrent chromosome translocations play a critical role in the pathogenesis of ALL, and many translocations have important prognostic signifi cance. Moreover, the molecular characterization of breakpoints from such rearrangements has led to the identifi cation of oncogenes and to the design of novel therapeutic approaches. The most common structural change is the t(12;21) translocation, which accounts for 25% of cases of ALL [12].
This study was presented the cytogenetic characteristics of pediatric patients diagnosed as having ALL within a 17-year period.

Materials and Methods
The childhood and adult ALL patients -referred to our genetics laboratory from 1 May 1992 to 28 April 2009 were recruited. The diagnosis of ALL was made on the basis of a chromosomal analysis. In this study, karyotypes of patients referred with AAL were retrospectively analysed. ALL was initially, diagnosed by the referring clinical hematologist, based on the available clinical details. The cytogenetic analyses were performed in the Cytogenetics Laboratory, at the Department of Medical Biology and Genetics, Faculty of Medicine, Çukurova University. Metaphase chromosome preparations from peripheral blood were made according to the standard cytogenetic protocols. Fifty metaphases were analyzed in all the patients, but in cases of abnormalities and mosaicism the study was extended up to 100 metaphases. All CAs were reported according to the current international standard nomenclature (ISCN, 2009).

Results
Cytogenetics was performed in 260 patients diagnosed with ALL. The male-female ratio was 1,5 and median age at diagnosis was 8,58 years. The incidence of abnormal karyotype was higher in males (n=43, 72,4%) than that of females (n=17, 27,6%). The male-female ratio with abnormal karyotype was 2,62. Out of 260 patients, 60 (23,1%) were found to have abnormal karyotype and rest of 200 (76,9%) were normal. The results of abnormal karyotype were divided into three categories: Philadelphia chromosome-positive (Ph+), CAs in addition to Ph+ and the others CAs wereshown in Table 1 The ratio of translocations in all CAs was 3,9% (10 cases),

Discussion
In present study diagnostically and prognostically important CAs were detected in 23,1% of patients by Cytogenetics.
But, date from Turkey using this system which was applied to speci mens from 34 ALL patients showed that CAs were detected in 74% of the patients [14]. It was reported that he frequency and spectrum of CAs were not similar between the cur rent study and previous reports in patients with ALL [10,11].
The frequency of genetic abnormalities observed in our study was lower than that of previous reports [14][15][16][17][18]. The difference between the fi ndings of our study and previous reports was our some patients show different clinical presentations which, sometime, are mixing with clinical features of CML, AML and AAL.
In our study, deletions was found to be most frequent structural abnormalities (5,8%), and 15 chromosomal deletions. Losses of these regions were identifi ed at 1p22, 4p13, 6q16, 6q-, 7q32, 7q11, 8q24, 11q11, 11q-, 12p13, 12q11, 14q22, 17p11, suggesting the presence of multiple tumor suppressor genes (Table 1). We were detected one del(1p22), two t(1;2)(q12;q37), t(1;11)(q21;q23), one dup(1)(q12; q23) and 1q+ in 5 patients. The numerical and structural aberrations of chromosome 1 have been observed in chronic and acute leukemias and solid tumors as well. Previous reports on a CML-BC patient found the involvement of the long arm of chromosome 1 [19]. It was marked that consistent breaks and deletions involving specifi c oncogenes/tumor suppressor genes were present in 1p36 and other regions of chromosome 1, such as 1p22-q21 [20,21]. It is remarkable to have found the ABL2 gene in 1q25, which is a proto-oncogene whose protein is a non-receptor tyrosine kinase, and the TPR gene in the same region; its extreme 5′ end fuses with several different kinase genes in some neoplasias and could be involved in leukemogenesis mechanisms [22]. Gene deletions and translocations are responsible for initiating of cancer progression. The loss or inactivation of one or more tumor suppressor genes are associated with many types of cancer, as chromosomal regions associated with tumor suppressors are commonly deleted or mutated.
Aberrations involving chromosome 6q are common in childhood ALL occurring in 7-18% of patients [23,24]. Frequently, the breakpoints are 6q15, 6q21-23 regions and interstitial deletion are also common in both B lineage and T lineage. Overall the breakpoints occur predominantly in 6q21 [25]. The deleted region is mostly large, involving a number of genes and genes affected by the deletion are presumably essential for normal cellular homeostasis. FOXO3A, a transcription factor involved in the control of proliferation and apoptosis, is one of the candidate genes located in the deleted 6q21 region. In the present study, 3 patients also had del(6q) and t(2;6)(p25;p21.3), and this break point was in the region of 6p21.3. Sinclair et al. [26] also suggested that the incidence of balanced rearrangements involving 6q in ALL may be much higher than previously thought. These fi ndings show that the (6q) abnormality is a good prognostic indicator. In present study, we also found del(7q) in two patients, and there was a correlation between an isolated deletions of the long arm of chromosome 7 (q31, q32 and q-) and patients with ALL. The partial deletions of 7q might represent a secondary event in the context of preexisting genomic instability. Complete loss of chromosome 7 or partial deletion involving its long arm are highly recurrent CAs in myeloid disorders [27,28]. Also, we found deletion at bands 8q24 in a patient. These results were consistent with the hypothesis that the 8q24 region affected the susceptibility of cancer.
Recurrent balanced translocations are observed in specifi c types of leukaemia and lymphomas, and are known to drive tumorigenicity [29,30]. About 50% of hematopoietic neoplasms is expressed in 80% of all infants with ALL [32]. In the present study, chromosomes 11 translocation was found to be most frequently involved in structural abnormalities (in six cases).
In particular, translocations between 11 and 4 chromosomes in three patients are noteworthy. Similarly, in other Turkish study, the t(11q23) translocation was found in one patient of thirty four patients with childhood ALL [14]. The chromosomal translocation t(4;11)(q21;q23) is associated with high-risk ALL In the present study, the Ph chromosome t (9;22) translocation was present in approximately 1,2% of children.
These chromosomal gains may be relevant to the pathogenesis of ALL transformation in some cases. Balanced rearrangements are infrequent and can occur as a single additional abnormality or as a part of complex cytogenetic changes. In our study, The inversions were evaluated in 2 patients (0,8%) such as inv (9) (p11;q12) and inv(2) ( Table 1). Some genes on chromosomes 2 that are known to play a role for tumor development. Therefore, 2p-q could play a role in the pathogenesis of ALL. However, there have been very few reports on the inv(9) variation as an acquired CAs in hematologic malignancies [36]. It has reported pericentric inversion in chromosome 9 at a frequency of 0,8-2% in normal population and at a similar frequency in ALL patients.
This inversion is usually considered as a polymorphism, and its clinical consequences remain unclear [37].
Autosomal recessive genetic diseases associated with increased chromosomal fragilitie (FSs) and a predisposition to ALL include ataxia-telangiectasia, Nijmegen breakage syndrome, and Bloom syndrome [38]. FSs are known to be associated with genes that relate to tumorigenesis. They have been found the FSs in 8-32% of our patients-cells (1,9%) (Table 1) (Table 1). Microchimerism is the existence of small amounts of DNA in the body coming from a geneticly different person. It recently found male microchimerism presence to be associated with a 70% reduced odds of developing breast cancer, and a 4-fold increased odds of developing colon cancer [39]. In one other study, FMc were identifi ed in 50% of papillary thyroid tumors [40]. Unfortunately, we were not able to determine the nature of these cells. This suggests to us that the can microchimerism take place in the etiology of cancer?
Numerous genetic alterations have been and continue to be discovered in ALL, and it has been repeatedly shown that specifi c genetic abnormalities are present in the majority of successfully karyotyped patients with ALL [3,41]. In the present study, 5% of the patients revealed numerical CAs (Table 1). The rate of chromosomal gains and losses can lead to aneuploidy was termed chromosomal instability. Aneuploidy is also features of cancers that are usually associated with poor prognosis. Aneuploidy is a remarkably common feature of human cancer, present in ~90% of solid human tumours and >50% of haematopoietic cancers [42]. The common aneuploidy observed in our patients (2,3%), occurring in 10-15% of metaphases (Table 1). Several studies have shown that aneusomies of different chromosomes were associated with aggressive tumor behavior [11,12]. For example, gain of chromosome 8 is found in ~10-20% of cases of acute myeloid leukaemia [43,44]. Autosomal monosomies are observed to be the most frequent in our patients, and the most frequently however, trisomy of chromosome 5 confers poorer outcome among highhyperdiploid patients [48,49]. In the present study, we observed the complete or partial loss of chromosome 7 in several metaphases (Table 1). Monosomy 7 was also observed in several clones analyzed. An association between the complete or partial loss of chromosome 7 and ALL has been recognized from the early days of tumor cytogenetic analysis. Detection of such abnormalities usually heralds a poor prognosis [50].
Amare [51], reported monosomy of chromosomes 7 and 17 as secondary CAs that occur when disease progresses from CML to a more aggressive blastic phase or transforms into lymphoid leukemialike acute myeloid, lymphoid leukemia, or lymphoid blast crisis of CML. Sabine [52], have shown that monosomy 7/del(7q) causes loss an important tumor suppressor, and upregulation of oncogene in AML.
With regard to Y chromosome, deletions have been shown to be involved in prostate cancer [60,61], male breast carcinomas [62,63], and pancreatic adenocarcinomas [64]. Loss of Y chromosomes is a common secondary change in cancer cells and in a few leukemias [65].

Ethics
Ethics Committee Approval: The study was a retrospective, the results analyzed in our laboratory were used.

Authorship Contributions
Concept