What is "sideroblastic anemia"

n. refractory anemia characterized by sideroblasts in the bone marrow [syn: sideroblastic anaemia, siderochrestic anemia, siderochrestic anaemia]

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). In sideroblastic anemia, the body has iron available but cannot incorporate it into hemoglobin, which red blood cells need to transport oxygen efficiently. The disorder 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).

Sideroblasts (sidero- + -blast) are atypical, abnormal nucleated erythroblasts (precursors to mature red blood cells) with granules of iron accumulated in the mitochondria surrounding the nucleus. Normally, sideroblasts are present in the bone marrow, and enter the circulation after maturing into a normal erythrocyte.

Ring sideroblasts are named so because iron-laden mitochondria form a ring around the nucleus. To count a cell as a ring sideroblast, the ring must encircle a third or more of the nucleus and contain five or more iron granules, according to the 2008 WHO classification of the tumors of the hematopoietic and lymphoid tissues.

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.