Variations in erythrocyte uroporphyrinogen I synthetase activity in non porphyrias

The activity of erythrocyte uroporphyrinogen I synthetase has been measured in various cases of non-porphyric affections. The results indicate a diminution of this activity in some of the studied cases of chronic renal insufficiency and chronic polyarthritis. This modulation in activity mitigates against its use as a diagnostic criterion of acute intermittent porphyria. On the other hand, an increase in urosynthetase activity has been noted in acute and especially chronic hepatic affections. This increase seems to be connected with the severity of the hepatic affection. The relationship is illustrated particularly in the case of viral hepatitis associated to an AIP, where the increasing activity of the urosynthetase masks for many weeks the congenital deficiency peculiar to this AIP. Our study thus indicates that the diagnosis of AIP based on the activity of the urosynthetase must take into account the pathological context in which the investigation is realised.