Clinical haematology · UKMLA & AKT
Megaloblastic anaemia
A free high-yield preview for the UKMLA Applied Knowledge Test, covering how to recognise this condition. The full SA Note notes add investigations, management and complications, with practice questions on this topic.
Key high-yield points
- B12/folate deficiency → reduced active tetrahydrofolate (THF) → impaired thymidylate synthesis → slowed DNA replication → nuclear-cytoplasmic dyssynchrony → megaloblasts + ineffective erythropoiesis
- B12 (only) also required for homocysteine → methionine → S-adenosylmethionine (SAM) → myelin synthesis; deficiency → demyelination of posterior and lateral spinal columns (subacute combined degeneration, SACD)
- Folate deficiency does NOT cause SACD - it does not affect this methylation pathway
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