Hematologic involvement in mitochondrial cytopathies in childhood: a retrospective study of bone marrow smears.

We retrospectively analyzed the bone marrow (BM) smears of 10 children with mitochondrial cytopathies. Light microscopic examination showed large and coalescent cytoplasmic vacuolization of some BM precursors in nine cases, including two children with normal peripheral blood counts and four with sideroblastic anemia. BM ultrastructural study showed abnormal mitochondria in the erythroid lineage in all three children studied. Ultrastructural studies in two cases revealed a population of giant mitochondria with abnormal ultrastructure coexisting with a population of normal mitochondria in proerythroblasts, basophil erythroblasts, and less commonly in more mature erythroblasts. In a third child, mitochondria were normal in size with cristae either absent or exhibiting abnormal longitudinal orientation. Heteroplasmic segregation of mitochondria during cell division could account for the finding of a double population of cells on ultrastructural examination. These features suggest that cytologic and ultrastructural BM examination could be useful for the diagnosis of mitochondrial disorders. That is, when large and coalescent cytoplasmic vacuoles of BM precursor cells are present, the clinician should search for mitochondrial cytopathy in a child with unexplained cytopenia(s).