Low frequency of NRAS and KRAS2 gene mutations in childhood myelodysplastic syndromes

Epigenetic alterations of p15(INK4B) and p16(INK4A) genes in pediatric primary myelodysplastic syndrome

We studied the methylation status of the p15(INK4B) and p16(INK4A) genes in 47 pediatric patients with primary MDS, its correlation with subtype, and the role of p15(INK4B) and p16(INK4A) in the evolution of MDS toward AML. Aberrant methylation of the p15(INK4B) gene was detected in 15 of 47 patients (32%), whereas only four patients demonstrated methylation of the p16(INK4A) gene (8%). The frequency of p15(INK4B) methylation was significantly higher in RAEB and RAEB-t subtypes (p<0.003). Aberrant methylation of the p16(INK4A) gene was also more frequent in the subtypes that characterize advanced stages of the disease (p<0.05). Evolution of disease was verified in 17 (36%) of the 47 patients. The association of p15(INK4B) and p16(INK4A) methylation status with evolution of disease was clearly significant (p<0.008 and p<0.05, respectively). These results suggest that methylation of the p15(INK4B) and p16(INK4A) genes is an epigenetic biomarker of pediatric disease evolution.

Myelodysplastic syndrome in children and adolescents

Myelodysplastic syndromes (MDS) are clonal disorders characterized by ineffective hematopoiesis and subsequent frequent development of acute myeloid leukemia (AML). In children and adolescents, MDS are uncommon disorders, accounting for less than 5% of hematopoietic malignancy, with great heterogeneity in presentation and clinical course. The genetic changes predisposing children to MDS are largely obscure. Monosomy 7 is the most common chromosomal abnormality, often occurring as a sole abnormality. The recent pediatric modification of the World Health Organization (WHO) classification has greatly facilitated the diagnostic process. Refractory cytopenia (RC) is the most common MDS subtype in children, occurring in about half of all MDS cases. There is consensus that the relationship between MDS with increased blast count and de novo AML is better defined by biological and clinical features than by blast count. Because monosomy 7 is the only chromosomal abnormality strongly suggestive of MDS, children presenting with a low blast count and other chromosomal aberrations or normal karyotype must be closely observed before a diagnosis of MDS can be established. With an increasing number of children surviving primary cancer with chemotherapy or radiation therapy, the incidence of secondary therapy-related MDS is rising. The MDS risk is also increased in patients with inherited bone marrow failure disorders; this relationship provides valuable insights into MDS biology. Allogeneic hematopoietic stem cell transplantation (HSCT) from a matched related or suitable unrelated donor is the choice for most children with MDS and can rescue a large proportion of patients.

Myelodysplastic and myeloproliferative disorders in children

PURPOSE OF REVIEW

Myelodysplastic and myeloproliferative disorders are clonal myeloid malignancies characterized by the triad of a growth advantage of clonal cells, disturbed differentiation and increased apoptosis. The rarity of these disorders in children and the lack of a widely accepted classification have contributed to the paucity of reports on these malignancies in the pediatric literature. A number of significant advances have been achieved in recent years. The present review will focus on diagnostics and therapy.

RECENT FINDINGS

International consensus has been achieved on classifying these disorders into three main groups; myelodysplastic syndrome (MDS), myeloid leukemia of Down syndrome (ML-DS) and juvenile myelomonocytic leukemia (JMML). In the last few years we have witnessed important advances, especially regarding the therapy of these disorders, and we have gained insights into the molecular pathogenesis of ML-DS and JMML.

SUMMARY

Classification of myelodysplastic and myeloproliferative disorders has been facilitated. Chemotherapy regimens for ML-DS have been reduced, resulting in fewer toxic deaths and improved survival. The results of stem-cell transplantation for MDS and JMML have improved. Insight into the molecular mechanisms involved may open new therapeutic avenues.

Lack of TP53 and FMS gene mutations in children with myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are rare disorders in children. Molecular mechanisms underlying MDS in children are not yet completely understood. Considering the role of FMS and TP53 gene mutations in adult MDS patients, we analyzed mutations of these genes in a cohort of 35 children with MDS. Single-strand conformation polymorphism polymerase chain reaction analysis performed on FMS codon 969 and TP53 exons 5-9 showed no mutations in the analyzed sequences. Our results suggest that molecular mechanisms of MDS evolution in children are different from those in adults.