Heme synthesis disorders: practice question

The best answer is A, Porphobilinogen deaminase. Acute intermittent porphyria results from partial deficiency of porphobilinogen deaminase.

Uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria, a severe photosensitive disease of infancy.

Uroporphyrinogen decarboxylase deficiency gives porphyria cutanea tarda, with blistering photosensitive skin and no acute attacks.

Ferrochelatase deficiency causes erythropoietic protoporphyria, with painful photosensitivity.

It tests Heme synthesis disorders in Biochemistry. ALA and porphobilinogen accumulate during attacks, causing abdominal and neuropsychiatric symptoms, and porphobilinogen turns urine dark on standing. There is no photosensitivity.

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.