Familial porphyria cutanea tarda with normal erythrocytic urodecarboxylase: an exception to the rule?

The possibility that the differentiation between sporadic and familial porphyria cutanea tarda cannot always be made on the basis of the measurement of the erythrocytic uroporphyrinogen decarboxylase activity has been examined. Two cases of porphyria cutanea tarda, with a normal erythrocytic enzyme activity in a father and son, are described. The authors exclude that these are 2 cases of sporadic or toxic porphyria cutanea tarda within the same family. These 2 cases provide additional evidence for the existence of a form of familial porphyria cutanea tarda in which erythrocytic uroporphyrinogen decarboxylase activity is normal.