He was started on salvage therapy with CLAG-M (cladribine 5 g/m2, cytarabine 2 g/m2, granulocyte colony-stimulating factor (G-CSF), mitoxantrone 10 g/m2), and after the first dose of filgrastim (G-CSF), he developed acute diplopia with leptomeningeal involvement by AML as identified by brain magnetic resonance imaging and lumbar puncture (Fig. 3). The gene discussed is CSF3; the disease is acute myeloid leukemia.