Myelodysplasia and myeloproliferative disorders in children.

Myelodysplastic syndromes (MDSs) are uncommon in pediatric patients; they account for less than 10% of hematopoietic malignancies. In about one third of children with MDSs there is a predisposing genetic condition. MDS in children is more difficult to classify using criteria applied to cases in adult populations, and there are often features present that bridge those of MDS and chronic myeloproliferative diseases. Two groups of MDSs are found in children: juvenile myelomonocytic leukemia, which is unique to infants and young children, and adult-type MDS. A high percentage of children with MDS have bone marrow cytogenetic abnormalities; monosomy 7 is the most common. Patients less than 1 year of age at diagnosis have a significantly better survival than older children. A low platelet count, elevated hemoglobin F (>15%), and complex cytogenetic abnormalities are unfavorable prognostic indicators. MDSs must be distinguished from the same nonneoplastic causes of myelodysplasia that occur in adults, but in addition there are a number of congenital disorders of hematopoiesis and inherited metabolic diseases that affect hematopoiesis in children.