Heme synthesis in sideroblastic anaemias

The underlying biochemical abnormalities common to all forms of sideroblastic anaemia appear to be associated with impaired heme synthesis in erythroid precursors. Present knowledge on the specific enzymatic defects of heme synthesis, which are thought to be the basis for the ring sideroblast abnormality, is presented in this review. Different forms of sideroblastic anaemia have different enzyme defects, but some of them might be secondary due to inhibition by mitochondrial iron overload. Some drugs and toxins may suppress heme synthesis and cause a reversible sideroblastic anaemia. Recent experimental studies have also provided detailed biochemical explanations for cases responding to pyridoxine therapy. Leukaemic transformation, which occurs in some cases of idiopathic sideroblastic anaemia, is not predictable on the basis of any abnormality of heme synthesis, but further impairment of heme synthesis seems to accompany the leukaemic development in such patients. So far, no association between the chromosomal aberrations and the defects of heme synthetic enzymes has been found.