Ring sideroblasts are erythroid precursors (immature red blood cells) found in the bone marrow that contain abnormal iron deposits arranged in a ring-like pattern around the nucleus. These deposits are located in mitochondria and are visualized using Prussian blue staining, which highlights iron granules.
Key Characteristics
- Defined by the presence of ≥5 iron-laden mitochondria encircling ≥1/3 of the nucleus in erythroblasts.
- Detected during a bone marrow aspirate with iron staining (e.g., Perl’s stain).
- Associated with ineffective erythropoiesis and anemia.
Clinical Relevance in MDS
- Found in MDS with ring sideroblasts (MDS-RS) — a subtype of low-risk MDS per WHO classification.
- Often linked to SF3B1 mutations, which correlate with a better prognosis.
- Predictive biomarker for response to luspatercept, an erythroid maturation agent.
Pharmacologic Implications
- ESAs (e.g., darbepoetin) may be ineffective if EPO levels are high or in transfusion-dependent patients.
- Luspatercept is FDA-approved specifically for MDS-RS or SF3B1-mutated MDS patients with transfusion-dependent anemia who have failed ESA therapy.
- Iron overload is common due to frequent transfusions → consider iron chelation (e.g., deferasirox).