We screened 19 patients with macrocytosis associated with various diagnoses including paroxysmal nocturnal hemoglobinuria, dyskeratosis congenita, acquired aplastic anemia, congenital neutropenia, Shwachman Diamond syndrome, diserythropoietic anemia (Gata1 mutation), and chemotherapy-related macrocytosis (Table 4). The gene discussed is GATA1; the disease is acquired aplastic anemia.