Received: 20 June 2016 Accepted: 11 July 2016 DOI: 10.1002/pbc.26185 Pediatric Blood & Cancer The American Society of Pediatric Hematology/Oncology LETTER TO THE EDITOR Expression and methylation status of MDR-1 gene in pediatric primary myelodysplastic syndrome Pediatric myelodysplastic syndrome (MDS) is an uncommon hemato- logic malignancy. 1 Allogeneic hematopoietic stem cell transplantation (HSCT) is the only treatment with curative potential for patients with MDS. 2–4 Chemotherapy has been used for higher risk group of MDS patients without a matched donor. However, complete remission rates in patients with MDS or MDS/acute myeloid leukemia (AML) are gen- erally lower than in patients with de novo AML treated with similar chemotherapy regimens. 5,6 An obstacle for the benefit of chemother- apy is multidrug resistance. 7 Here, we report the expression and the methylation status of MDR-1 gene in pediatric patients with MDS and its association with subtypes and karyotypes. We studied 34 patients with pediatric primary MDS. These patients included 21 males and 13 females, with ages between 3 months and 18 years (mean 8 years). The patients were diagnosed at National Cancer Institute; Martagão Gesteira Institute of Pediatrics and Child Develop- ment, Arthur Siqueira Cavalcanti Hematology Institute, Rio de Janeiro, Brazil. Diagnosis and classification were done according to the cri- teria of Hasle et al.. 8 Healthy bone marrow samples were obtained from seven bone marrow transplant children donors (mean 8 years). This study was approved by Ethics Committee of National Cancer Institute. Clonal chromosomal abnormalities were detected in 32% of patients. Abnormal karyotypes were observed mainly in refractory anemia with excess of blasts (RAEB) and in refractory anemia with excess of blasts in transformation (RAEB-t) than in refractory cytope- nia (RC). Analyses of MDR-1 gene expression were performed by real- time quantitative PCR in 34 pediatric patients with MDS and 7 healthy pediatric controls. The median, 1.9, of MDR-1 relative expression levels in patients was higher than the median, 1.0, in controls (Fig. 1A). MDR- 1 relative expression levels showed a similar median (1.9) for the ini- tial subtype, CR, and advanced subtypes, RAEB/RAEB-t (Fig. 1B). We observed that patients with abnormal karyotypes showed a median 2.9 for MDR-1 relative expression levels and patients with normal karyotypes showed a median of 0.9 (Fig. 1C). These results were not statistically significant (Mann–Whitney test). The precise mechanisms underlying the transcriptional upregulation of MDR-1 gene are not fully understood. So, we investigated the methylation status of MDR-1 gene promoter region. This analysis was done in 34 pediatric patients with MDS, 7 healthy pediatric controls and the cell lines K562 and MCF-7. The methods used were Combined Bisulfite Restriction Anal- ysis (COBRA) and High Resolution Melting (HRM). The results showed absence of methylation for pediatric patients and healthy children. The Grant sponsor: CNPq Grant sponsor: FAPERJ. FIGURE 1 Analysis of mRNA relative expression of MDR-1 gene. (A) MDR-1 gene expression from samples of healthy donors and pediatric MDS patients, (B) in MDS subtypes, and (C) in normal and abnormal karyotypes results of both techniques were confirmed by sequencing using the ABI PRISM 3100 Genetic Analyzer (Applied Biosystems, USA). Some studies showed that MDR-1 expression was associated with presence of blast cells and abnormal karyotype in adult patients with MDS. 9,10 Our results suggest that altered expression of the MDR-1 gene may be an intrinsic feature of MDS, contributing to resistance to treatment with chemotherapy. The increased expression of the MDR-1 gene may be a marker aiding in the indication of treatment with allo- geneic HSCT. CONFLICT OF INTEREST The authors declare that there is no conflict of interest. Pediatr Blood Cancer 2016;00: 1–2 c  2016 Wiley Periodicals, Inc. 1 wileyonlinelibrary.com/journal/pbc