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Old 12-06-2013
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Biochemistry Biochemistry questions about porphyria?

why doesn't iron deficiency cause symptoms of porphyria like lead poisoning, i.e to cause acquired porphria?

second Q,
photosensitivity occurs in porphria cutanea tarda duo to elevation of porphyrin, so why doesn't this occur with lead poisoning and iron deficiency??
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Old 12-06-2013
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There are other types of porphyrias, but the ones that are tested on the exam happen to be Acute intermittent and Cutanea tarda.

Another form of porphyria can be caused be an inherited defect in ferrochelatase, and its called Erythropoietic Protoporphyria (EPP). Theoretically speaking it would make sense that a decrease decrease in iron could lead to a build up of protoporphyrin which would also cause EPP. Why doesnt EPP occur due to iron deficiency? I dunno but my guess is that the level of iron deficiency required to cause EPP would be so drastic as to have caused other symptoms/death before the porphyria occurs.

Lead poisoning is less likely to lead to a porphyria because lead also inhibits the second step of heme synthesis (d-ALAD enzyme) thus you wont get a significant build up of the causative substrates.

Why doesn't the USMLE test EPP? I dunno, but just be glad its one thing less for you to learn.
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Old 12-06-2013
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Quote:
Originally Posted by khaled_elfert View Post
why doesn't iron deficiency cause symptoms of porphyria like lead poisoning, i.e to cause acquired porphria?

second Q,
photosensitivity occurs in porphria cutanea tarda duo to elevation of porphyrin, so why doesn't this occur with lead poisoning and iron deficiency??

second Q: Photosensitivity in porphyria cutanea tarda is caused by accumulation of the substrate uroporphyrinogen (defect of uroporphyrinogen decarboxylase). Neither lead poisoning nor iron deficiency cause accumulation of uroporphyrinogen (d-ALA or protoporphyrin would accumulate).
I think it was in kaplan somewhere....
You can check this out, if you want to be more specific: http://www.ncbi.nlm.nih.gov/pubmed/2488874
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