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Porphyria and its types : Medical biochemistry USMLE step 1

Porphyria refers to a disease caused by abnormal biosynthesis of a porphyrin. Heme is one of the most studied porphyrins.
Congenital erythropoietic porphyria is inherited in an autosomal recessive fashion, causing mutations of uroporphyrinogen III synthase (UROS).
The symptoms of congenital erythropoietic porphyria are photosensitivity and anemia.
Erythropoietic protoporphyria is the most common porphyria in children.
Erythropoietic protoporphyria is inherited in an autosomal recessive manner, causing a mutated enzyme ferrochelatase
Patients with erythropoietic protoporphyria suffer from non-blistering photosensitivity and sometimes gallstones.
Acute intermittent porphyria is caused by an autosomal dominant mutation in the gene that encodes the enzyme porphobilinogen deaminase, leading to attacks of diffuse pain around the abdomen due to autonomic dysfunction.
Porphyria cutanea tarda is caused by a mutation in the gene encoding for the enzyme uroporphyrinogen decarboxylase, leading to chronic blistering skin lesions with elevated levels of hepatic transaminases.
Hepatitis C is associated with porphyria cutanea tarda.
Variegate porphyria, which used to be called mixed porphyria, is an autosomal dominant disorder due to a mutation for protoporphyrinogen oxidase.
The symptoms of variegate porphyria are blistering photosensitivity and abdominal pain, although they are milder than in acute intermittent porphyria.
All of the porphyrias we have discussed except for erythropoietic protoporphyria have blistering skin lesions.
On histology, the vesicles are subepidermal in location and lead to significant thickening of the superficial dermal vessels.
In porphyrias, IgG deposits and other proteins are seen in these vessel walls under direct immunofluorescence.
In porphyrias, the dermal vessel walls are thickened by glassy deposits of serum proteins.

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