Congenital Erythropoietic Porphyria
Gary P. Carlson
A rare congenital disorder of hemoglobin production that is inherited as an autosomal recessive has been recognized primarily in Holstein cattle, but it has also been reported in other breeds.4-7 Commonly called “pink tooth,” the disorder is characterized by slow growth rates in calves, photosensitization, and exfoliation of nonpigmented skin when exposed to sunlight, reddish-brown teeth, and modest anemia.
The teeth and bones exhibit a pink fluorescence under ultraviolet light, and the presence of uroporphyrin turns urine a brownish-red color. The condition is present at birth, and the metabolic defect is a hereditary deficiency of the enzyme uroporphyrinogen III synthase (UROS), which catalyzes an essential step in the synthesis of the porphyrin structure of hemoglobin. This leads to accumulation of uroporphyrin and coproporphyrin, which deposit in the teeth, where they are concentrated in the dentin, bones, and other tissues. The anemia seen in these cattle is variable among individuals, and several factors contribute to it. Reduced intravascular red cell life span is related to the high concentration of uroporphyrin and Coproporphyrin within the cells. Porphyrins may induce hemolysis and delay red cell series maturation in the bone marrow, although there is often evidence of active erythropoietic response in peripheral blood.5 There is no treatment for this inherited disorder, but genetic counseling is advisable. Substantial efforts have been made to reduce the incidence of this disease in the Holstein breed. Affected cattle have much lower levels of UROS than normal cattle, and carrier animals have intermediate levels of this enzyme. Despite their rather serious problems, these cattle do reasonably well if housed indoors out of direct sunlight. The principal differential consideration is chronic fluorosis, which also produces brown discoloration of the teeth, but they do not fluoresce under ultraviolet light.Another form of altered porphyrin metabolism, erythropoietic porphyria, has been described in humans and cattle.5 In humans the mode of inheritance is autosomal dominant, whereas in cattle the disorder appears to have a recessive pattern of inheritance and may be sex linked because it is only seen in females. The disease does not produce anemia, porphyrinuria, or teeth discoloration, but ferrochelatase (heme synthase) deficiency leads to high concentrations of erythrocyte and fecal protoporphyrins.
Porphyria has also been reported in swine, where it exhibits a dominant pattern of inheritance.5 Health effects are minimal, and there is no photosensitivity, but the pigs' teeth have reddish- brown discoloration.
Finally, animals may develop acquired toxic porphyrias. This can occur with heavy metal poisonings, principally lead. Lead inhibits several key enzymes of heme synthesis. Inhibition of aminolevulinate dehydrase leads to accumulation of aminolevulinic acid, and decreased aminolevulinate dehydrase activity is a sensitive indicator of lead poisoning. Lead also inhibits ferrochelatase and leads to marked elevation of erythrocyte zinc protoporphyrin IX, making measurement of zinc proto- porphyn IX levels a means of monitoring lead exposure.5
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- Bibliography
- Smith Bradford P., Van Metre David C., Pusterla Nicola (eds.). Large Animal Internal Medicine. Part 2. 6th edition. — Elsevier,2020. — 2279 p., 2020