Abnormal Red‐Cell Metabolism of Pyridoxine Associated with β‐Thalassaemia

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Abstract
Summary. Red-cell conversion of pyridoxine to pyridoxal phosphate was studied in control subjects, and patients with heterozygous and homozygous β-thalassaemia. In 7% of control subjects the rate of pyridoxine conversion was well below the range found in the other control subjects (5.0–8.6%, mean 6.5%/g Hb × 10−2) but in heterozygous β-thalassaemia was below that range in 63% of the patients. The conversion rate was also slow or borderline in the majority of patients with severe transfusion-dependent homozygous β-thalassaemia, in spite of the presence of some donor cells; but was normal, or fast as in other anaemias, in all but one patient with mild homozygous thalassaemia. There was a much higher incidence of a slow conversion rate in the parents of the severe homozygotes than in parents of the mild homozygotes, illustrating the familial pattern. This supports our view that the red-cell conversion rate of pyridoxine is an inherited characteristic, independent of thalassaemia. The cause of a reduced rate of pyridoxine conversion was investigated. The increase to a normal rate following riboflavin ingestion suggests a defect in the activity of the flavin mononucleotide (FMN)-dependent pyridoxine phosphate oxidase.