Congenital Sideroblastic Anemia

What is congenital sideroblastic anemia?

Congenital sideroblastic anemia (CSA) occurs when the bone marrow fails to produce a sufficient number of healthy red blood cells. Instead, it produces sideroblasts (abnormal red blood cells that normally mature into red blood cells) in which iron accumulates in the mitochondria. These iron-loaded mitochondria surround the nucleus of the developing red blood cell and give the appearance of a ring.

Because the iron is stuck in the mitochondria, the body cannot incorporate it into hemoglobin, which red blood cells need to transport oxygen efficiently throughout the body. This defect in red blood cell production also can alter the iron balance within your child, often resulting in total body iron overload.

Sideroblastic anemia can be either congenital (inherited) or acquired (not inherited). Both types have very different causes, treatments and prognoses.

What are the types of sideroblastic anemia?

Acquired anemia

Sideroblastic anemias can be divided into congenital and acquired forms. Acquired anemias are more common and are seen almost exclusively in older adults. They usually are the result of acquired non-inherited genetic mutations that occur only in the red blood cell precursors leading to ringed sideroblasts. This form of sideroblastic anemia — refractory anemia with ringed sideroblasts (RARS) — is classified within a broader group of diseases called myelodysplastic syndromes (MDS) and can eventually lead to leukemia. In more than 75% of cases of RARS, the bone marrow cells have acquired a mutation in one particular gene called SF3B1. Acquired sideroblastic anemias can also be due to nutritional deficiencies, acquired metabolic diseases or toxins.

Anemia from a genetic mutation

By contrast, the congenital sideroblastic anemias (CSAs) are inherited diseases caused by genetic mutations that are present at birth in all the cells. Even though the mutations are inherited and present at birth, anemia may not be present in infancy and sometimes may not be recognized until adulthood. Therefore, it is particularly important to distinguish late-onset CSA from an acquired sideroblastic anemia, because they have very different causes, treatments and prognoses.

How we care for CSA

Children and adolescents with CSA are treated at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center through our Rare Anemias and Iron Disorders Program. Our Rare Anemias and Iron Disorders Program provides comprehensive care for children with all types of rare anemias and iron disorders, as well as ongoing medical management and access to new treatment approaches through our clinical research.