The levels of delta-aminolevulinate are elevated in all patients with porphyria because of the loss of feedback inhibition of d-ALA synthase by haem. Haem usually prevents the translation of d-ALA synthase by activating a protein which binds to the 5'-untranslated region of the mRNA.
In acute porphyrias the activity of porphobilinogen deaminase is either normal or low resulting in the accumulation of porphobilinogen (PBG). The combination of high d-ALA and PBG results in the abdominal pain and neuropsychiatric features.
In non-acute porphyrias the acitivity of PBG deaminase is elevated and so PBG does no accumulate. There are specific defects in the the subsequent metabolism of proto-porphyrins. Accumulation of protoporphyris causes the photosensitivity.
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