PB1914: CYTOGENETIC FINDINGS IN 18 CHILDREN WITH MYELODYSPLASTIC SYNDROMES BY KARYOTYPIC AND FISH ANALYSIS

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Background: Pediatric myelodysplastic syndromes (MDS) are rare disorders characterized by hematopoietic cell dysfunction, an increased risk of AML and a poor prognosis. Although it is known that cytogenetic abnormalities are seen in approximately half of children diagnosed with MDS, their detailed cytogenetic profile has not been elucidated yet due to the rarity of the disease. Aims: We tried to detect chromosomal abnormalities in pediatric patients with MDS, including submicroscopic aberrations such as gene alterations associated with the disease and possible malignant transformation by karyotypic and molecular cytogenetic analysis (fluorescence in situ hybridization, FISH) to contribute to the elucidation of the cytogenetic profile of pediatric MDS and the investigation of the pathogenesis of the disease. Methods: In this study 18 children with MDS are included. Karyotypic analysis was performed on 24h, 48h and 72h bone marrow (BM) cultures using GTG-banding. Karyotypic analysis was carried out on 25 at least metaphases. FISH analysis was performed on cultured BM cells using IVD probes for centromere (CEP) of chromosomes 7 and 8 and the chromosomal regions 7q22, 7q31, 8q24(MYC), 11q22.3(ATM), 11q23(MLL), and 17p13(TP53). For each sample at least 200 interphase cells (iFISH) and 5 metaphases (mFISH) were analyzed to increase sensitivity. Normal cut-off was estimated at 3%. Results: The sex ratio was 1,25 (10 M/8 F) and the mean age was 9,42 years (range 0,4y - 19y). Eleven patients had RCC, 5 MDS-EB and 2 t-MDS. Normal karyotypes were detected in 10 patients (55,6%), 6 patients with RCC, 3 with MDS-EB and 1 with t-MDS. Abnormal karyotypes were found in 8 patients (44,4%), 4 with RCC, 2 with MDS-EB and 1 with t-MDS. Monosomy 7 was observed in 2/18 patients (>70% of metaphases), +8 in 2/18 patients (5-6.6% of metaphases), inv(17)(p11.2q21) in 1/18 patients (18.75% of metaphases), complex karyotypes in 2/18 patients (31.3-73.2% of metaphases including abnormalities of 1q, 2q, 4q, 5q, 16q, 18 and Xp), in one patient after SCT in the transformation of MDS into s-AML and in the other at diagnosis with t-MDS) and chromatid and chromosome breaks in 1/18 patients, (8,6-9,6% of metaphases) in 2 different BM samples taken with an interval of 3 months, which were also found in his brother’s BM karyotype. FISH revealed -7 in 2/18 patients confirming their karyotypes, loss of one p53 allele in 3/18 patients at low frequencies (6,5%, 4,5%, 3,5%) all with hypocellular RCC and transfusion-dependency that underwent SCT, +8 in 2/18 (in 8% and 2,7% of cells) confirming trisomy 8 in their karyotypes and loss of one MLL allele and MLL rearrangement in a patient that was transformed to s-AML in 4,4% of cells. A normal pattern of hybridization was observed for the above probes in the rest cases and for MYC and ATM genes in all the examined cases. Summary/Conclusion: Karyotypic aberrations were detected in 44,4% of children including -7, +8, inv(17), complex karyotypes and chromatid and chromosome breaks, revealing that other chromosome aberrations except -7/del(7q) and trisomy 8 are characterized this disease. Clonal chromosome abnormalities can be detected at low frequencies in the karyotypes of pediatric MDS patients so except from iFISH, mFISH is also needed especially in cases with small clones or submicroscopic translocations. The low frequency of submicroscopic aberrations such as p53 deletions observed in 3 cases of hypocellular RCC must be confirmed in larger studies by molecular analysis as they may play a potential role in MDS pathogenic evolution.