Vitamin B6Metabolism in Idiopathic Sideroblastic Anaemia and Related Disorders

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Abstract
Patients with idiopathic anemias associated with abnormal sideroblasts were defined according to morphologic and ferrokinetic criteria and the hematologic and biochemical effects of vitamin B6 therapy were evaluated. While all patients presented similar clinical pictures, peripheral blood changes and bone marrow abnormalities, 2 distinct groups were identified by sideroblast morphology and ferrokinetics. Patients with more than 5% true ring sideroblasts in the marrow (IRSA) uniformly had marked ineffective erythropoiesis, while those with abnormal sideroblasts but few true ring forms were hypoproliferative. Measurements of red cell pyridoxine kinase (PnK) and intracellular pyridoxal 5-phosphate availability (PLP) as assessed by the activity of the PLP-dependent enzyme aspartate aminotransferase (EGOT), revealed slightly decreased PnK levels in IRSA subjects but normal intracellular PLP activities in both groups. When treated with pyridoxine, all patients showed increases in red cell PnK and EGOT activities which were similar to those seen in normal subjects. Treatment with PLP also effectively increased erythrocyte vitamin B6 activity. Neither pyridoxine nor i.m. PLP improved erythropoiesis as determined by serial hematocrits, reticulocyte counts and erythron Fe turnover measurements. Since both therapies increased red cell protoporphyrin levels and the excretion of urinary coproporphyrin in a number of subjects, the possibility that impaired hemesynthesis in the sideroblastic anemias was associated with abnormal vitamin B6 metabolism at the level of the mitochondrion must still be considered.