ERYTHROCYTE UROPORPHYRINOGEN DECARBOXYLASE ACTIVITY - DIAGNOSTIC-VALUE AND RELATIONSHIP WITH CLINICAL-FEATURES IN HEREDITARY PORPHYRIA-CUTANEA-TARDA

A marked discrepancy between mild and late clinical features and a nea rly complete absence of erythrocyte uroporphyrinogen decarboxylase act ivity (Ery-UROD activity) was observed in a case of inherited porphyri a cutanea tarda. The entity and time of appearance of clinical feature s, the onset of clinical symptoms after exposure to contributing facto rs, the effectiveness of phlebotomies and heterozygosity of the mother alone for uroporphyrinogen decarboxylase (UROD) deficiency were typic al for familial porphyria cutanea tarda (F-PCT), whereas the extremely low UROD activity was peculiar to hepatoerythropoietic porphyria (HEP ). These observations indicate that: 1) Ery-UROD activity may not alwa ys be useful to discriminate between F-PCT and HEP; 2) Ery-UROD activi ty does not always correlate with clinical symptoms; 3) in inherited U ROD deficiency, the genetic defect may be heterogeneous. Finally, the observed discrepancy may provide additional evidence for the existence of tissue-specific isozymes.