Caracterização das alterações cromossômicas e moleculares em síndrome mielodisplásica primária na infância no Estado do Rio de Janeiro

Abstract

The primary myelodysplastic syndrome (MDS) is rare in childhood, representing about 4% of all pediatric hematologic malignancies. The natural history of this disease is extremely variable, some patients may have milder forms, with high survival and low rate of leukemic transformation. However, about 10 to 40% of cases progress to acute myeloid leukemia (AML). This work had as principal aim analyse bone marrow cells of pediatric patients with primary MDS for their cytogenetic, molecular and clinical features, in order to identify genetic and epigenetic markers to aid diagnosis and prognosis, as well as to contribute for the knowledge of alterations that lead to disease development and its evolution to AML. Our results showed the presence of abnormal karyotypes in 56.5% (65/115) in pediatric patients with primary MDS. According to the classification of childhood MDS, 78 patients had CR, 22 RAEB and 15 RAEB-t. It was included in our study three patients with Down Syndrome who had MDS. In more advanced disease subtypes the frequency of cases with chromosomal abnormalities was higher. The most frequent chromosomal abnormalities were -7/7q and del(11q). Cytogenetic analyses aided in the diagnosis of cases with suspected of primary pediatric MDS and it was an important tool for the treatment choice. The study of the presence of methylation in the promoter region of p15INK4b and p16INK4a genes revealed that 28.6% (22/77) showed methylation for the p15INK4b gene and only 7.8% (6/77) for the p16INK4a gene, being the higher frequencies observed in more aggressive subtypes of MDS. The methylation analysis of the MDR- 1 gene showed that both, the bone marrow samples from 7 health individuals (bone marrow donors) as the 77 pediatric patients, showed unmethylation at the investigated region. Methylation at p15INK4b gene showed a strong association with abnormalities involving chromosome 7, suggesting a possible pathway of disease progression. The analysis of relative expression of MDR -1 and EZH2 genes showed that both genes had high expression levels in patients with MDS compared to the health individuals. The median of relative expression levels of EZH2 and MDR-1 genes in MDS patients was higher than the median obtained in donors. The relative expression levels of EZH2 gene were higher in the RAEB / RAEB-t subtypes. However, the relative expression levels of MDR-1 gene were similar in CR and RAEB / RAEB-t. Regarding karyotypes, we observed that abnormal karyotypes showed higher relative expression levels of EZH2 and MDR-1 when compared with normal karyotypes. Our results suggest that the chromosomal alterations, -7/7q-, del (11)(q23) and complex karyotype; and the presence of methylation in p15INK4b are associated with poor prognosis and they are probably biomarkers of disease evolution.