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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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