Immunoreactive uroporphyrinogen decarboxylase in porphyria cutanea tarda.

Immunoreactive uroporphyrinogen decarboxylase was measured by rocket immuno-electrophoresis in haemolysates from 7 unrelated patients with familial porphyria cutanea tarda (PCT), 6 patients with sporadic PCT, and 7 normal subjects. In all patients with familial PCT immunoreactive enzyme protein was decreased (51% of normal), to the same extent as catalytic activity (56% of normal), whereas in sporadic PCT both measurements were normal. These results show that familial PCT is commonly caused by a mutation which does not lead to the production of non-catalytic cross-reactive immunological material. Familial PCT can be distinguished from other types of PCT by a simple immunoelectrophoretic method that does not involve measurement of uroporphyrinogen decarboxylase activity and which is therefore likely to be suitable for routine diagnostic use.