The clinical and laboratory findings in two brothers with severe anemia are presented. These findings were very similar in both cases. Evidence that at least one of them suffered from a pyridoxine-responsive anemia is presented. It was assumed that the other had the same disorder since, in addition to the striking similarity in the clinical and laboratory abnormalities, the latter’s anemia disappeared completely with the parenteral administration of vitamin B complex, which provided him with 2 mg. of pyridoxine daily. These patients have not relapsed 1.5 and 6 years after stopping the therapy.

A review of the reported cases with anemia responding to vitamin B6 administration is presented. Common factors observed in some of these cases are: (1) severe anemia, microcytic and hypochromic in type, chiefly due to a striking maturation erythroblastic arrest at the basophilic stage with no defect in leukocytes or thrombocytes; (2) hyperferremia and hemosiderosis; (3) an abnormal tryptophan-loading test; and (4) complete or almost complete correction of all abnormalities with administration of vitamin B6, even at small doses. These data were considered to suggest that the patients had a true deficiency in pyridoxine.

In other patients, no increased excretion of xanthurenic acid has been observed after a tryptophan-loading dose, and pyridoxine administration has improved the anemia only partially and has not reversed the serum iron parameters to normality. All of these other patients suffered from a familial hypochromic anemia not due to iron deficiency or from a "sidero-achrestic" or "refractory normoblastic" anemia.

The cause of the disorder in patients in the first group is unknown, but, by exclusion, increased requirement of vitamin B6 seems to be the most likely possibility.

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