Myelodysplasia in childhood may be a polyclonal disease

Myelodysplasia in childhood can be associated with constitutional abnormalities. Two main situations can be observed: constitutional diseases such as Down’s Syndrome may be the first step of a malignant stem cell transformation leading to monoclonal hematopoiesis. However, in other situations such as mitochondrial cytopathies or other polymalformative syndromes, myelodysplasia may simply be the hematological expression of a multi-tissue constitutional disease. In such cases, the bone marrow karyotype is usually found to be normal and, in affected females, clonality studies show a polyclonal pattern. Clonality assessment should be, when possible, a mandatory step before any major therapeutic decision during the course of childhood myelodysplasia.