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what are the causes of porphyria and porphyria

what are the causes of porphyria and porphyria

Etiology of porphyria

Etiology of porphyria

I. Etiology:

All eight enzymes in heme biosynthesis pathway have been cloned, sequenced and chromosomally located. Mutations in the erythrocyte-specific form of ALA synthase have been found in some X-linked sideroblastic anemia. Porphyria and related diseases are associated with the deficiency of seven other enzymes whose mutant genes have been identified. Although various types of hereditary porphyria are associated with specific enzyme deficiencies, a certain number of patients with enzyme deficiencies come from the same family, and it seems that enzymes have different mutant genes. Therefore, these diseases are heterogeneous at the molecular level.

Second, the pathogenesis:

When enzymes in the heme biosynthetic pathway are deficient, their substrates and heme precursors can accumulate in bone marrow or liver. These heme precursors increase in the blood, are transported to other tissues, and are excreted with urine and feces.

Some porphyria, especially porphyria with elevated porphyrin precursors ALA and PBG, can damage nerves and have many symptoms, such as abdominal pain and myasthenia, which can develop into muscle paralysis. It is speculated that the pathogenesis of neurological symptoms is excessive heme intermediate products acting in nervous system or lack of heme synthesis in nervous system. However, ALA and other heme metabolites have not been proved to be neurotoxic, and no heme deficiency has been found in the nerve tissue of patients. The exact pathogenesis is still unclear.

Porphyria, which causes the increase of porphyrins in tissues and plasma (such as uroporphyrin, coproporphyrin and protoporphyrin), may have photosensitivity. In the presence of O2, when these porphyrins are irradiated by light with wavelength of 400nm, they can produce charged unstable oxygen, called singletoxygen, which can cause tissue damage. Skin is particularly sensitive because it is the tissue most exposed to light.


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