Effect of pyridoxine deficiency on porphyrin precursor excretion in acute intermittent porphyria

Abstract

Experimental pyridoxine deficiency was induced in a patient with acute intermittent porphyria by means of a synthetic diet and administration of deoxypyridoxine. Determination of urinary excretion of pyridoxic acid, oxalate and xanthurenic acid, and of the total circulating lymphocytes, confirmed the presence of pyridoxine deficiency during the experimental period. The patient was asymptomatic both during and prior to the study, which was terminated after fifteen days due to the development of an optic neuritis. Urinary excretion of Δ-amino-levulinic acid (ALA) and porphobilinogen declined significantly during the period of proved pyridoxine deficiency and increased again following the administration of pyridoxine. Tryptophan loading tests suggested that the patient may have had a relative intracellular pyridoxine deficiency prior to the study. The results are consistent with other evidence that Δ-amino-levulinic acid synthetase is the rate-limiting enzyme in porphyrin biosynthesis in man.