[Acquired, vitamin B6-responsive, primary sideroblastic anemia, an enzyme deficiency in heme synthesis]

The activity of delta-aminolevulinic acid synthetase (ALAS), the rate-limiting enzyme in heme synthesis, has been found to be markedly reduced (13% of controls) in erythroblasts of a patient with acquired, primary sideroblastic anemia. Administration of vitamin B6 (pyridoxin, 200-600 mg/d) resulted in complete reconstitution of erythroblastic ALAS-activity with concomitant disappearance of all hematologic abnormalities. The findings show that the therapeutic efficacy of pyridoxin in primary sideroblastic anemia is due to its effect on defective ALAS. More generally, the data support the view that almost all features of primary sideroblastic anemia can be ascribed to a disturbance of heme synthesis in erythroblasts.