Variant of acute intermittent porphyria with normal erythrocyte uroporphyrinogen-I-synthase activity.

A kindred in which several members have otherwise typical acute intermittent porphyria but normal erythrocyte uroporphyrinogen-I-synthase activity has been described from Finland. We studied two porphyric members of this kindred, two patients with typical acute intermittent porphyria, and two healthy controls using the delta-aminolaevulinic acid loading test and by measuring the erythrocyte enzymes of haem biosynthesis. The excretion pattern of haem precursors after the delta-aminolaevulinic loading test in the members of the kindred studied, was similar to that in typical acute intermittent porphyria suggesting an identical enzyme defect in the liver. The activity of all red cell enzymes studied was normal in the members of the kindred. The results suggest that porphyria in the kindred studied is a variant of acute intermittent porphyria, where the uroporphyrinogen-I-synthase defect is manifested in the liver but not in red cells.