Sideroblastic Anemia

Sideroblastic anemia or sideroachrestic anemia is a disease in which the bone marrow produces ringed sideroblasts rather than healthy red blood cells (erythrocytes). It may be caused either by a genetic disorder or indirectly as part of myelodysplastic syndrome, which can evolve into hematological malignancies (especially acute myelogenous leukemia). In sideroblastic anemia, the body has iron available but cannot incorporate it into hemoglobin, which red blood cells need to transport oxygen efficiently.

Sideroblasts are atypical, abnormal nucleated erythroblasts (precursors to mature red blood cells) with granules of iron accumulated in perinuclear mitochondria. Sideroblasts are seen in aspirates of bone marrow.

Ring sideroblasts are named so because of the arrangement of the iron granules in a ring form around the nucleus. However it does not take the ring to be complete in order to count a cell as a ring sideroblast. According to the 2008 WHO classification of the tumors of the hematopoietic and lymphoid tissues, it only needs 5 or more iron granules encircling one third or more of the nucleus.

The WHO International Working Group on Morphology of MDS (IWGM-MDS) defined three types of sideroblasts:

1. Type 1 sideroblasts: fewer than 5 siderotic granules in the cytoplasm
2. Type 2 sideroblasts: 5 or more siderotic granules, but not in a perinuclear distribution
3. Type 3 or ring sideroblasts: 5 or more granules in a perinuclear position, surrounding the nucleus or encompassing at least one third of the nuclear circumference.