Decreased Red Cell Uroporphyrinogen I Synthetase Activity in Intermittent Acute Porphyria
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Discussion
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Implication
Biochemical evaluation demonstrates approximately 50% decreased red cell uroporphyrinogen I synthetase in intermittent acute porphyria, suggesting a reliable test for the heterozygous state.
Key Points
- To determine whether hepatic uroporphyrinogen I synthetase deficiency extends to erythrocytes and can distinguish intermittent acute porphyria from other genetic hepatic porphyrias.
- Assayed uroporphyrinogen I synthetase activity in red cell hemolysates from nonporphyric subjects, patients with genetic hepatic porphyria, and members of a large affected family pedigree.
- Calculated the apparent Michaelis constant (Km) of partially purified erythrocyte uroporphyrinogen I synthetase across cohorts.
- Erythrocyte uroporphyrinogen I synthetase activity was selectively decreased to approximately 50% of normal exclusively in patients with intermittent acute porphyria.
- The apparent Km of partially purified enzyme was 6 x 10^-6 M in both nonporphyric controls and patients with intermittent acute porphyria.
- Family pedigree screening demonstrated that reduced erythrocyte enzyme activity reliably identifies individuals carrying the heterozygous genetic state.
Cite This Study
Strand et al. (1972) studied this question.