Sideroblastic anemia, or sideroachrestic anemia, is a form of anemia in which the bone marrow produces ringed sideroblasts rather than healthy red blood cells (erythrocytes). The most common form of congenital sideroblastic anemia (CSA) is caused by mutation of erythroid-specific 5-aminolevulinate synthase (ALAS2), the first enzyme of heme synthesis in erythroid cells.