Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Recognise defective mitochondrial haem synthesis, distinguish inherited, clonal and reversible acquired causes, interpret ring sideroblasts correctly, and treat the driver while preventing transfusional iron injury.
Haem synthesis partly occurs in erythroblast mitochondria. When synthesis, iron-sulphur handling or mitochondrial function fails, imported iron cannot be incorporated effectively and accumulates around the nucleus. The marrow may be erythroid rich because precursors expand but die before release, producing anaemia despite abundant stored iron. Peripheral cells can be microcytic in congenital ALAS2 deficiency, macrocytic in clonal disease or mixed after transfusion and variable clone expression.
The diagnostic task is to explain the ring-sideroblast phenotype. Begin with count, reticulocytes, film and iron studies, then reconstruct exposures and nutritional risk. Basophilic stippling supports but does not prove lead toxicity. Low copper and caeruloplasmin with excess zinc or malabsorption require careful interpretation. In an older adult with persistent unexplained cytopenia, marrow morphology, cytogenetics and a myeloid mutation panel assess a myelodysplastic neoplasm. In a younger person or lifelong microcytosis, genomic evaluation may identify congenital sideroblastic anaemia.
Variants in ALAS2 and other mitochondrial or iron-sulphur genes impair haem production, sometimes causing childhood disease and sometimes an X-linked phenotype recognised only in adulthood.
Alcohol, lead, copper deficiency and medicines including isoniazid or prolonged linezolid can disrupt mitochondrial haem synthesis or cofactor availability.
Myelodysplastic neoplasms with SF3B1 mutation or related clonal abnormalities produce ring sideroblasts alongside ineffective, dysplastic haematopoiesis and age-dependent risk of progression.
Iron enters erythroblast mitochondria but cannot be incorporated normally into protoporphyrin, leaving perinuclear iron-laden organelles visible with Prussian-blue staining.
Abnormal erythroblasts undergo intramedullary death, so the marrow can be hypercellular while reticulocyte output and circulating haemoglobin remain inappropriately low.
Suppressed hepcidin from ineffective erythropoiesis can increase absorption, and repeated transfusion adds non-excretable iron, eventually threatening liver, heart and endocrine organs.
Mixed microcytic and normocytic or macrocytic populations can widen red-cell distribution and obscure the mechanistic pattern in a single MCV.
Low haemoglobin with raised ferritin and transferrin saturation despite no iron prescription suggests ineffective use rather than simple deficiency.
Abdominal pain, neuropathy or cognitive symptoms with basophilic stippling and occupational risk raises lead toxicity requiring confirmation.
New severe cytopenias, circulating blasts, infection or bleeding needs urgent myeloid-neoplasm assessment rather than routine nutritional follow-up.
Anaemia plus neutropenia and sensory ataxia after bariatric surgery or high zinc exposure should prompt copper evaluation.
Both conditions may be microcytic, but iron deficiency usually has depleted ferritin and transferrin saturation rather than abundant marrow iron and systemic loading.
Globin-chain imbalance causes microcytosis with characteristic haemoglobin or genomic findings; target cells and family ancestry differ, although both may develop iron excess.
Inflammatory iron restriction produces low circulating iron with preserved or raised ferritin but does not ordinarily create pathological perinuclear ring sideroblasts.
Clonal cytopenia without ring sideroblast predominance can show macrocytosis and dysplasia; integrated marrow and molecular classification determines the correct neoplasm category.
Absorptive and transfusional iron can cause hepatic fibrosis, cardiomyopathy, diabetes, pituitary dysfunction and arthropathy if burden remains unrecognised.
Persistent ineffective erythropoiesis may require repeated red-cell support, increasing alloimmunisation, reaction and iron-loading risk while complicating future transplantation.
Clonal sideroblastic myelodysplasia can acquire excess blasts or evolve to acute myeloid leukaemia, with risk determined by the full genetic and clinical profile.
The diagnostic morphology is iron-loaded mitochondria arranged around the erythroblast nucleus, not merely any iron granules within a precursor.
Congenital, toxic and clonal mechanisms can generate different or mixed cell sizes, so a normal average can conceal two populations.
Deficiency causes cytopenia and marrow dysplasia, making surgical and zinc histories crucial before assigning an irreversible clonal diagnosis.
Ineffective haem synthesis leaves iron unused and may suppress hepcidin, so low haemoglobin must not trigger automatic oral iron.
Prescribing iron for every microcytic sideroblastic anaemia.
Calling ordinary sideroblasts pathological ring forms.
Missing zinc-driven copper deficiency after surgery.
Using basophilic stippling as proof of lead poisoning.
Continuing high-dose pyridoxine without response or neuropathy review.
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A patient after bariatric surgery develops anaemia, neutropenia and sensory ataxia. Marrow examination reports ring sideroblasts and vacuolated precursors. Which reversible cause should be assessed?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
Prolonged high-dose exposure can cause sensory neuropathy; document indication, neurological baseline and response rather than continuing an ineffective trial indefinitely.
Identify and remove the driver, avoid unmonitored over-replacement and recognise that neurological recovery may lag or remain incomplete after blood counts normalise.
Monitor blood pressure, thrombosis, bone pain and haemoglobin rise; discontinue according to non-response rules and do not use outside the defined disease category.