On the basis of the uroporphyrinogen decarboxylase ( UD ) activity in the erythrocytes, and the family history of the disease, different types of porphyria cutanea tarda ( PCT ) can be distinguished. In some cases, however, the distinction may involve some uncertainty (overlapping of subgroups). The question arises of whether the current erythrocyte UD activities in the different types of PCT are determined merely genetically. The erythrocyte UD activities in 72 unrelated patients with different forms of PCT (62 with type I PCT and 10 with type II PCT ), in different stages of the disease, were measured in order to test whether the activity exhibits any change during the long period of recovery. In both types the activities were faintly but significantly increased, from 94.9% (in PCT I) or 54.3% (in PCT II) up to 98.4% or 56.1% respectively. In both types the lower activity in the untreated condition can be attributed to a combination of several factors, including oxidative damage to UD , which results in a minor additional inhibition of the genetically determined enzyme activities.
Modified uroporphyrinogen decarboxylase activity in a yeast mutant which mimics porphyria cutanea tarda