A 3½-year-old boy was admitted to the hospital with a history of pallor, abdominal distention, and abnormal eye movements for 2½ months. His mother had used unidentified medicines during her pregnancy, which was reported as normal. He was the first child of parents who were distantly related.
The boy's weight, height, and head circumference were 5 kg, 57 cm, and 40 cm, respectively. On physical examination, he had bilateral nystagmus and optic atrophy. The liver and spleen were enlarged. On admission, hemoglobin measured 88 g/L and the white blood cell count was 23.3×109/L. A peripheral blood smear showed hypochromic erythrocytes, a reduced number of platelets, and numerous promyelocytes, myelocytes, metamyelocytes, myeloblasts, and normoblasts. Bone marrow aspiration was performed with difficulty, and the marrow smear resembled that of the peripheral blood. Multiple blast forms were also evident on the marrow smear. Results of