Multiple choice

Acute intermittent porphyria is due to defect in

  1. uroporphyrinogen III cosynthase

  2. porphobilinogen deaminase

  3. protoporphyrinogen oxidase

  4. coproporphyrinogen oxidase

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B Correct answer
Explanation

Acute intermittent porphyria (AIP) is caused by a deficiency of porphobilinogen deaminase (also known as hydroxymethylbilane synthase), which is the third enzyme in the heme biosynthesis pathway. This deficiency causes accumulation of porphobilinogen and ALA, leading to acute neurovisceral attacks. The other enzymes listed are deficient in different types of porphyria: uroporphyrinogen III cosynthase in congenital erythropoietic porphyria, protoporphyrinogen oxidase in variegate porphyria, and coproporphyrinogen oxidase in hereditary coproporphyria.

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