Deficiency of porphobilinogen synthase associated with acute crisis. Diagnosis of the first two cases in Chile by laboratory methods.

Erythrocyte porphobilinogen synthase deficiency was confirmed by the determination of its activity in blood and also by the high levels of both porphyrins and 5-aminolaevulinic acid in the urine of two siblings. They presented with a picture of porphyric attack characterized by abdominal colic pain, high blood pressure, tachycardia and severe constipation. The profile of both porphyrins and their precursors in urine and blood resembled lead poisoning. However, this was ruled out because both patients had normal blood levels of lead. Furthermore, porphobilinogen synthase activity did not normalize when it was determined in the presence of dithiothreitol or dithiothreitol plus zinc chloride. No other causes to account for a deficiency in porphobilinogen synthase activity were identified. The simultaneous occurrence of similar clinical and biochemical symptoms suggests that the same triggering factor was present. Because the activity of porphobilinogen synthase was less than 4% of normal values, it is possible that these patients were homozygotes with respect to this defect, which could explain the presence of clinical symptoms. We propose that this metabolic defect is not uncommon and it should be kept in mind when diagnosing of porphyrias or heavy metal intoxications.