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). This evidence concerns the gene GATA1 and Shwachman-Diamond syndrome.