The presence of major symptoms in DHFR deficiency. (A) Bone marrow biopsy showing a severely impaired erythroid outgrowth and a myeloid differentiation defect with marked megaloblastic features (hematoxylin and eosin; bar, 20 μm). (B) Immunohistochemistry with antiglycophorin A, demonstrating the presence of multiple megaloblasts and an almost complete absence of late-stage erythroid precursors. Among the unstained (myeloid) cells, several giant bands are identified (arrows). (C) AML was suggested in the second case. Immunohistochemically stained slide of the spleen. CD33-positive blasts marked as (b) can be observed in lytic tissue of the spleen. Some of these blasts are located in capillaries. The nuclei of the endothelial cells lining the wall of these capillaries are indicated with an arrow. Similar infiltration of MPO/CD33+ myeloid blasts was observed in the liver and bone marrow. The child died at presentation in the emergency room. The diagnosis of infantile AML was made post mortem from the obtained autopsy samples. (D) T2 magnetic resonance imaging in patient 3 demonstrating both cerebral and cerebellar atrophy and hypoplasia of the cerebellar vermis.