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, i ncluding two children with normal peripheral blood counts and four with sid eroblastic anemia. BM ultrastructural study showed abnormal mitochondria in the erythroid lineage in all three children studied. Ultrastructural studi es in two cases revealed a population of giant mitochondria with abnormal u ltrastructure coexisting with a population of normal mitochondria in proery throblasts, basophil erythroblasts, and less commonly in more mature erythr oblasts. In a third child, mitochondria were normal in size with cristae ei ther absent or exhibiting abnormal longitudinal orientation. Heteroplasmic segregation of mitochondria during cell division could account for the find ing of a double population of cells on ultrastructural examination. These f eatures suggest that cytologic and ultrastructural BM examination could be useful for the diagnosis of mitochondrial disorders. That is, when large an d coalescent cytoplasmic vacuoles of BM precursor cells are present, the cl inician should search for mitochondrial cytopathy in a child with unexplain ed cytopenia(s).