Familial and sporadic porphyria cutanea: two different diseases.

Uroporphyrinogen (URO) decarboxylase was measured in hemoglobin-free erythrocytes from subjects with familial porphyria cutanea: the mean activity was about 50% of that found in erythrocytes from normal subjects. Asymptomatic carriers were always found in the family. No enzyme deficiency was found in erythrocytes from subjects with sporadic porphyria cutanea. The measurement of URO decarboxylase in erythrocytes seems to allow an easy distinction between these two groups of porphyria cutanea.