Erythropoietic Porphyria of the Fox Squirrel Sciurus niger

Comparative Aspects of Porphyriain Man and Animals *

“…In fact, although the average cosynthetase activity in 18 gray squirrels was 8900 unitdg Hb, activity was not detectable in the blood of 13 fox squirrels at a sensitivity limit of 200-400 units/g Hb. 30 This difference is greater than that between normal and porphyric cattle, or normal and porphyric human beings. Even after the squirrels were bled to elevate the reticulocyte count, a procedure that markedly increased cosynthetase activity in gray squirrel red cells, cosynthetase activity was not measurable in the peripheral blood of fox squirrels.3o…”

“…Even in squirrels, a direct comparison of synthetase activity in blood of porphyric and nonporphyric animals is complicated by an effect of the age of the cells on the blood synthetase activity. 30 The relationship between synthetase activity in hemolysates and the reticulocyte count is shown in FIGURE 6. Between 1 and 16% reticulocytes, synthetase activity is not higher in gray than in fox squirrels, and may even be lower.…”

“…The feline condition is probably inherited as an autosomal dominant,38 and the predominance of isomer I in red cells and urine is not as great as it is in the bovine and human di~eases.3~. 30 In porphyric cats, red cell and tissue cosynthetase activities are at least as high as in normal animals,4o and marrow ALA synthetase activity is increa~ed.~? This condition, then, is probably not a cosynthetase-deficiency disease and may be a primary regulatory disorder.…”

Disease, race, geography and genes

“…Still more interesting, and rather enigmatic, is the fact that a certain ground squirrel (Sciurus niger) always has porphyria without suffering from it [2]. According to the literature all individual squirrels of that species have a red skeleton and red urine because of excess formation of uroporphyrin.…”

Comparative Aspects of Porphyria in Man and Animals*

“…In fact, although the average cosynthetase activityin 18 gray squirrels was 8,900 units/g Hb, activity was not detectable in the blood of 13 fox squirrels a t a sensitivity limit of 200-400 units/g Hb. 30 This difference is greater than that between normal and porphyric cattle, or normal and porphyric human beings. Even after the squirrels were bled t o elevate the reticulocyte count, a procedure that markedly increased cosynthetase activity in gray squirrel red cells, cosynthetase activity was not measurable in the peripheral blood of fox squirrels3 O Now, how can data indicating a virtual absence of cosynthetase from fox squirrel red cells be reconciled with normal hemoglobin production by these animals?…”