Variegate porphyria (VP) and acute intermittent porphyria (AIP), the two most common types of acute porphyrias (AHPs), result from a partial deficiency of protoporphyrinogen oxidase (PPOX) and hydroxymethylbilane synthase (HMBS), respectively.
Mean porphobilinogen deaminase activity in the erythrocytes of twenty-one patients with variegate porphyria was 8.37 +/- 1.99 nmol of uroporphyrin 1 erythrocytes-1 s-1, a 28% reduction (P less than 0.001) from normal (11.98 +/- 2.11).
Studies of the enzymes of haem biosynthesis in peripheral blood cells showed a dual enzyme deficiency, with reduced activity of both porphobilinogen deaminase, as seen in acute intermittent porphyria, and protoporphyrinogen oxidase, as seen in variegate porphyria.
We have so far identified 50 different mutations among 4 genes associated with the most common porphyrias showing a high molecular heterogeneity: 22 in the hydroxymethylbilane synthase (HMBS) gene (AIP), 7 in the protoporphyrinogen oxidase (PPOX) gene (VP), 16 in the uroporphyrinogen decarboxylase (UROD) gene (PCT) and 5 in the ferrochelatase (FECH) gene (EPP).