Laboratoire d'hématologie et département de pédiatrie, hôpital de Bicêtre, 78, rue du Général-Leclerc, 94270 Le Kremlin-Bicêtre.
Human mitochondrial DNA encodes proteins required for the energetic metabolism. Its mutation rate is ten to twentyfold higher than the mutation rate of the nuclear DNA. The mitotic segregation of mitochondria during development results in the coexistence, with various percentage, of normal and abnormal mitochondriae within the same cell; it explains the heterogeneity of the phenotypical expression of the mitochondrial cytopathy from one tissue to another. A lot of constitutional disorders are now related to a mutation or deletion of the mt-DNA. Pearson's syndrome, associating sideroblastic anemia with pancreatic insufficiency, has been the first identified mitochondrial cytopathy involving hematological dysfunction. Hematological anomalies can be, for several years, the sole expression of the disease, and are characterized by vacuolization of hematopoietic precursors. Acquired abnormalities of the mt-DNA could also account for some myelodysplastic syndromes in adult patients.