very heterogeneous:

I- idiopathic MDS

II- secondary MDS: to previous chemo- and/or radio-therapy

III- genetic MDS: cases associated with a congenital genetic disease, such as:
-neurofibromatosis type 1 (Von Recklinhausen) (MIM 16220): an hamartoneoplastic syndrome Kostmann syndrome (MIM 20270): also called congenital neutropenia
-Bloom syndrome (MIM 21090): a chromosome instability syndrome Dubowitz syndrome (MIM 22337): mimicks Blooms, but without chromosome instability
-Fanconi anaemia (MIM 22765): a chromosome instability syndrome
-Schwachman syndrome (MIM 26040): with pancreatic insufficiency, and risksof leukaemia
-Pearson disease (MIM 26056) and other mitochondrial diseases: they often share pancreatic insufficiency, bone marrow pancytopenia with myelodysplastic features but maintained polyclonality, muscular and other ubiquitous manifestations
-familial monosomy 7
-familial platelet storage pool deficiency
-unbalanced constitutional karyotypes, including +21, +8,del(11q), del(21q) miscellaneous conditions.

RA, RARS (very rare) , RAEB, RAEBT, CMML, Juvenile CML, Infantile Monosomy 7, non classifiable cases according to the FAB; with variable proportions according to the studies

10% of haematological malignancies in children; median age: 2 to 5 yrs; sex ratio: balanced for some, male predominance (in RAEB±T or CMML) for others

CR is obtained; however, median survival is about 3 yrs, while 1/3 of the cases may be considered as cured; good prognostic features are: young age, female sex, normal karyotype, and some of the genetic predisposing factors; worse prognosis is found in secondary MDS, RAEB and RAEBT, cases with +8, +19, t(1;7).