PB1912: MYELODYSPLASTIC SYNDROME WITH ISOLATED 5Q DELETION AND ASSOCIATED 5Q DELETION TO 13Q DELETION

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Background: The 5q deletion is the classic chromosomal abnormality in myelodysplastic syndrome (MDS). Critical regions are 5q31 and 5q33, leading to gene haplodeficiency and other pathogeneic mechanisms. 13q deletion occurs in about 2% of MDS cases. This deletion involved band 13q14. Aims: Here we describe cytogenetic abnormalities in a Tunisian cohort of MDS patients and we shed the light on cases with 5q deletion. Methods: Cytogenetic analyses of bone marrow cells were performed according to standard procedures for 12 Tunisian patients presenting with MDS. Cytogenetic analysis was performed on lymphocytes and bone marrow cells. Cultured cells were treated with colchicine and hypotonic KCl solution. The pellet was fixed and washed in methanol-acetic acid (3:1). The cells were resuspended in fixative and dropped onto slides. Chromosome-banding analysis was performed using RHG and GTG banding techniques. Three karyotypes and 25 metaphases were analyzed according to the International System for Human Cytogenetic Nomenclature. Results: Cytogenetic abnormalities were detected in 9 cases and del5q was recorded in four patients (3 patients with refractory anemia (RA) and a fourth with RA and excess blasts-T (RAEB-T)). The del5q was isolated in two RA cases as a del (5) (q13 q33) in a new diagnosed and a treated patients. It was associated in two patients: a RA patient explored during the evolution, harboring a del (5) (q12 q33) associated to a del (13) (q12 q14) and the RAEB-T patient harbouring a del (5) (q21 q31) associated to a clonal hyperploidy. Summary/Conclusion: The diagnosis of MDS was based on cytomorphology and cytogenetics. However, nowadays, an increasing number of molecular aberrations have been discovered and included in the WHO revised new classification of myeloid neoplasms. The del13q described in MDS seems to be a marker of the evolution of the clonal cells harboring 5q deletion. However, the molecular basis and the implicated genes of the deletion of the long arm of chromosome 13 associated to the 5q deletion clone remain until now not well explored.