BOF: General (The Porphyrias)

Which of the following factors has NOT been implicated in the triggering an attack of acute intermittent porphyria?

a) Acute hepatitis

b) Excessive sunlight exposure

c) Prolonged starvation

d) Psychological stress

e) Stage of menstrual cycle

Answer:

b) Excessive sunlight exposure

Explanation:

AIP is triggered by accumulation of toxic haem precursors due to deficiency in enzymes of the haem biosynthetic pathway. The enzyme delta-aminolevulinic acid synthases (ALA) is subject to feedback inhibition by haem, and stimulated (hence leading to accumulation of toxic intermediates prior to the enzyme deficient step) by cytochrome P450 enzyme inducers (amongst other drugs), starvation, menstrual cycle regulated hormones and stress. Photosensitivity is caused by accumulation of photosensitive porphyrins, not encountered in AIP.

Reference:

Balwani, M.; Desnick, R.J. The porphyrias: Advances in diagnosis and treatment. Blood 2012, 120, 4496–4505