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# Sideroblastic anaemia

Anaemia in which red cell precursors take in iron but cannot build haemoglobin, so iron piles up around their nucleus forming «ring sideroblasts».

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Sternum](https://durgical.com/en/anatomy/sternum/)
- [Ribs (back part)](https://durgical.com/en/anatomy/ribs/)

## Why it happens

- [Heavy metals: lead, mercury, arsenic and cadmium](https://durgical.com/en/general-pathology/heavy-metals-lead-mercury-arsenic-and-cadmium/)
- [Heme synthesis](https://durgical.com/en/biochemistry/pathways/heme-synthesis/)
- [ALA synthase](https://durgical.com/en/biochemistry/enzymes/ala-synthase/)
- [Vitamin B6 (pyridoxal phosphate)](https://durgical.com/en/biochemistry/molecules/vitamin-b6/)

## What it is

A group of inherited or acquired anaemias caused by a defect in haem synthesis inside the mitochondria of red cell precursors. Iron accumulates in the mitochondria around the nucleus, forming ring sideroblasts seen with Prussian blue stain on bone marrow.

## Who gets it

Uncommon. Acquired forms are more frequent than inherited ones; among them, myelodysplastic syndrome with ring sideroblasts affects older adults, and reversible forms follow alcohol use disorder, lead exposure, certain drugs or copper deficiency. X-linked sideroblastic anaemia, the most common inherited form, mainly affects males. In Colombia, lead exposure from informal battery recycling and mining, and alcohol use disorder, are reversible causes worth considering.

## Causes

- Inherited: X-linked sideroblastic anaemia from ALAS2 mutations (the first enzyme of haem synthesis, which needs vitamin B6); rarer autosomal and mitochondrial forms
- Myelodysplastic syndrome with ring sideroblasts (often SF3B1 mutation)
- Alcohol use disorder
- Lead poisoning (blocks ferrochelatase and ALA dehydratase)
- Drugs: isoniazid (vitamin B6 antagonism), chloramphenicol, linezolid; copper deficiency or zinc excess

## Risk factors

- Male sex and family history (X-linked form)
- Older age (myelodysplastic form)
- Heavy alcohol use and malnutrition
- Occupational or environmental lead exposure
- Tuberculosis treatment with isoniazid without vitamin B6 supplementation

## Pathophysiology

Haem is made by adding iron to protoporphyrin inside mitochondria. When an enzyme in this pathway fails (ALAS2 in the X-linked form; ferrochelatase in lead poisoning; vitamin B6-dependent steps with isoniazid or alcohol), iron keeps entering the mitochondria but cannot be used. Iron-loaded mitochondria ring the nucleus of erythroblasts, many die in the marrow (ineffective erythropoiesis), and the low haemoglobin increases intestinal iron absorption, leading to systemic iron overload even without transfusions.

## Classification

- Congenital: X-linked (ALAS2), autosomal recessive and syndromic mitochondrial forms
- Acquired clonal: myelodysplastic syndrome with ring sideroblasts
- Acquired reversible: alcohol, lead, drugs, copper deficiency, zinc excess

## Symptoms and signs

- Tiredness, weakness and breathlessness on effort
- Pallor
- Palpitations
- Signs of iron overload in long-standing disease: bronze [skin](https://durgical.com/en/anatomy/skin/), enlarged liver, diabetes or heart failure
- Associated features of the cause: neuropathy (isoniazid, lead), abdominal pain (lead), signs of chronic alcohol use

## Red flags

- Heart failure or arrhythmia from cardiac iron overload
- Falling blood counts in more than one line or rising blasts (myelodysplastic syndrome progressing)
- Encephalopathy, colic or wrist drop suggesting lead poisoning

## Diagnosis

**Clinical**
Suspect it in microcytic or dimorphic anaemia that does not respond to iron, especially when ferritin is high, or in anaemia with alcohol, lead or isoniazid exposure.

**Tests**
Blood count: microcytic anaemia in inherited and many reversible forms, or normocytic-macrocytic in the myelodysplastic form, often with a dimorphic red cell population and basophilic stippling (notably in lead poisoning). Iron studies: high serum iron, high ferritin and high transferrin saturation, unlike iron deficiency. Bone marrow aspirate with Prussian blue (Perls) stain showing ring sideroblasts is diagnostic. Blood lead level, copper and zinc, genetic testing for ALAS2, and cytogenetics and SF3B1 testing when myelodysplasia is suspected.

**Imaging**
Cardiac and [liver](https://durgical.com/en/anatomy/liver/) MRI (T2*) to measure iron overload in patients with chronic disease or frequent transfusions.

## Differential diagnosis

- Iron deficiency anaemia (low ferritin and saturation)
- Thalassaemia trait
- Anaemia of chronic disease
- Lead poisoning without ring sideroblasts
- Megaloblastic anaemia and other myelodysplastic syndromes

## Goal of treatment

Remove reversible causes, correct the anaemia where possible and prevent damage from iron overload.

## Treatment

**Medical**
Pyridoxine (vitamin B6) for the X-linked form and for isoniazid-related cases; many patients respond partially or fully.

**Conservative**
Removal of the cause: stopping alcohol, withdrawing the offending drug, eliminating lead exposure (with chelation for significant lead poisoning) and correcting copper deficiency.

**Medical**
Iron overload: phlebotomy when the haemoglobin allows it, or iron chelators (deferoxamine, deferasirox) in transfusion-dependent patients.

**Medical**
Myelodysplastic form: transfusions and erythroid maturation agents such as luspatercept, or erythropoiesis-stimulating agents.

**Follow-up**
Regular blood counts, ferritin and organ checks; nursing care includes transfusion safety, teaching about avoiding iron supplements and alcohol, and prophylactic vitamin B6 with isoniazid.

## Complications

- Iron overload damaging the heart, liver and [pancreas](https://durgical.com/en/anatomy/pancreas/) (heart failure, cirrhosis, diabetes)
- Transfusion dependence
- Progression of the myelodysplastic form to acute myeloid leukaemia (uncommon)
- Complications of the underlying cause (lead encephalopathy, alcohol-related disease)

## Prognosis

Reversible forms resolve when the cause is removed. Pyridoxine-responsive X-linked disease has a good outlook if iron overload is controlled. The myelodysplastic form with ring sideroblasts is usually a lower-risk myelodysplastic syndrome with relatively long survival.

## Prevention

- Vitamin B6 supplementation during isoniazid treatment
- Reducing occupational and environmental lead exposure
- Treatment of alcohol use disorder

## Test yourself

Think of the answer, then tap the question to see it.

## What stain shows ring sideroblasts in the bone marrow?

Prussian blue (Perls) stain for iron.

## How do iron studies in sideroblastic anaemia differ from iron deficiency?

Serum iron, ferritin and transferrin saturation are high, whereas they are low in iron deficiency.

## Which enzyme is defective in X-linked sideroblastic anaemia, and what cofactor does it need?

ALA synthase 2 (ALAS2), which needs vitamin B6 (pyridoxal phosphate).

## Which antituberculosis drug can cause sideroblastic anaemia?

Isoniazid, by antagonising vitamin B6.

## Which peripheral smear finding suggests lead poisoning?

Basophilic stippling of red cells.

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## Related conditions

- [Iron deficiency anaemia](https://durgical.com/en/conditions/iron-deficiency-anaemia/)
- [Thalassemias (α and β)](https://durgical.com/en/conditions/thalassemias/)
- [Anaemia of chronic disease (anaemia of inflammation)](https://durgical.com/en/conditions/anaemia-of-chronic-disease/)
- [Myelodysplastic syndromes](https://durgical.com/en/conditions/myelodysplastic-syndromes/)
- [Lead poisoning](https://durgical.com/en/conditions/lead-poisoning/)
- [Alcohol use disorder](https://durgical.com/en/conditions/alcohol-use-disorder/)
- [Isoniazid toxicity](https://durgical.com/en/conditions/isoniazid-toxicity/)
- [Hereditary hemochromatosis](https://durgical.com/en/conditions/hereditary-hemochromatosis/)
- [Megaloblastic anaemia (B12 or folate deficiency)](https://durgical.com/en/conditions/megaloblastic-anaemia/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [X-linked sideroblastic anemia](https://medlineplus.gov/genetics/condition/x-linked-sideroblastic-anemia/) (MedlinePlus Genetics (U.S. National Library of Medicine), 2025).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/sideroblastic-anaemia/