MT-CO1 and myelodysplastic syndrome with ring sideroblasts: Two mutations within the mtDNA gene COX I (complex IV of the electron transport chain) at positions 6742 (T>C) and 6721 (T>C) were identified in individuals suffering from acquired idiopathic sideroblastic anaemia (AISA), suggesting these are pathogenic mutations which cause respiratory chain dysfunction by inhibiting the reduction of Fe3+ to Fe2+ (Gattermann et al., 1997).