Acute Promyelocytic Leukemia (APL) is a subset of Acute Myeloid Leukemia (AML) that is clinically characterized by gene rearrangements involving the Retinoic Acid Receptor Alpha (RARα) and by the infiltration of bone marrow and/or blood by leukemic cells that resemble promyelocytes. The gene discussed is RARA; the disease is acute myeloid leukemia.