Acute intermittent porphyria (AIP) is the major autosomal dominant acute hepatic porphyria. This disease is caused by a deficiency in porphobilinogen deaminase, an enzyme of heme biosynthesis. Patients afflicted with this disease would be expected to excrete excess amounts of which of the following?

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Quizplus · Accepted Answer

In acute intermittent porphyria, there is a deficiency in porphobilinogen deaminase, leading to the accumulation and excess excretion of d-aminolevulinic acid (ALA) and porphobilinogen, which are upstream substrates in the heme biosynthesis pathway.  Porphobilinogen (PBG) deaminase (also called hydroxymethylbilane synthase) catalyzes the heme biosynthesis reaction involving the head-totail condensation of 4 molecules of porphobilinogen to produce the linear tetrapyrrole intermediate, hydroxymethylbilane. Hydroxymethylbilane can nonenzymatically cyclize into uroporphyrinogen I which is why PBG deaminase is also known as uroporphyrinogen I synthase. d-aminolevulinic acid (ALA) is the precursor for porphobilinogen, thus a defect in PBG deaminase would lead to excess ALA excretion.

Acute Intermittent Porphyria (AIP) Is the Major Autosomal Dominant Acute