Characterization of phosphofructokinase-deficient canine erythrocytes

Preclinical Research in Glycogen Storage Diseases: A Comprehensive Review of Current Animal Models

GSD are a group of disorders characterized by a defect in gene expression of specific enzymes involved in glycogen breakdown or synthesis, commonly resulting in the accumulation of glycogen in various tissues (primarily the liver and skeletal muscle). Several different GSD animal models have been found to naturally present spontaneous mutations and others have been developed and characterized in order to further understand the physiopathology of these diseases and as a useful tool to evaluate potential therapeutic strategies. In the present work we have reviewed a total of 42 different animal models of GSD, including 26 genetically modified mouse models, 15 naturally occurring models (encompassing quails, cats, dogs, sheep, cattle and horses), and one genetically modified zebrafish model. To our knowledge, this is the most complete list of GSD animal models ever reviewed. Importantly, when all these animal models are analyzed together, we can observe some common traits, as well as model specific differences, that would be overlooked if each model was only studied in the context of a given GSD.

Hemolysis, myopathy, and cardiac disease associated with hereditary phosphofructokinase deficiency in two Whippets

Two male castrated Whippet littermates were presented at 1 year of age for pallor, tachycardia, systolic heart murmur, dark yellow to orange feces, intermittent lethargy, pigmenturia, and muscle shivering or cramping after exercise. Persistent macrocytic hypochromic anemia with marked reticulocytosis and metarubricytosis was found when CBC results were compared with reference values for Whippets. Increased serum creatine kinase activity and hyperkalemia also were sometimes present over the 4-year period of evaluation. Progressively increasing serum concentrations of N-terminal prohormone brain natriuretic peptide suggested cardiac disease. Erythrocytes from the whippets were less osmotically fragile but more alkaline fragile than those from control dogs. Erythrocyte phosphofructokinase (PFK) activities and 2,3-diphosphoglycerate concentrations were decreased. Restriction enzyme-based DNA test screening and DNA sequencing revealed the same mutation in the muscle-PFK gene of the Whippets as seen in English Springer Spaniel dogs with PFK deficiency. This is the first report of PFK deficiency in Whippet dogs. In addition to causing hemolysis and exertional myopathy, heart disease may be a prominent clinical component of PFK deficiency in this breed and has not been previously recognized in PFK-deficient English Springer Spaniels.

Metabolic findings in the erythrocytes of cardiopathic and anaemic dogs

Few data are available on the activities of canine erythrocyte enzymes and on 2,3 diphosphoglycerate (2,3DPG) concentrations in pathological conditions other than heritable erythrocyte defects. Because some diseases might affect erythrocyte metabolism and oxygen transport, we evaluated these parameters in 10 healthy dogs and in dogs with symptomless dirofilariosis (n = 9), mild (n = 13) and severe (n = 8) cardiac failure, and haemolytic anaemia (n = 8). To evaluate possible membrane damage, the osmotic fragility of the red cells was measured. No haematological abnormalities were found in the dogs with mild cardiopathy or in those with symptomless dirofilariosis. Severe anaemia and neutrophilic leucocytosis were found in the dogs with haemolytic anaemia and, to a lesser degree, in those with severe heart failure. In dogs with these two diseases, elevated values obtained were, respectively: pyruvate kinase (PK) 17.5 +/- 10.3 U/g haemoglobin (Hb) (P < 0.001) and 11.6 +/- 7.5 U/g Hb (P < 0.01); glucose-6-phosphate dehydrogenase (G6PDH) 8.9 +/- 5.4 U/g Hb (P < 0.001) and 5.6 +/- 4.2 U/g Hb; 2,3DPG 21.8 +/- 4.9 U/g Hb (P < 0.001) and 22.5 +/- 4.1 U/g Hb (P < 0.001). The increased 2,3DPG concentrations may have been due to diminished oxygen availability but the observed enzymatic changes were attributed mainly to the presence of young red blood cells: there was a positive correlation between nucleated red blood cells and PK activity, G6PDH activity and 2,3DPG concentration and a negative correlation between mature erythrocytes and PK activity, G6PDH activity and 2,3DPG concentration. This was supported by the derivative curve of the fragiligram, which showed two or three peaks corresponding to different erythrocyte populations and by the negative correlation between the maximum haemolytic NaCl concentration and the reticulocyte number. The measurement of PK and G6PDH activity and of the 2,3PG concentration, together with information provided by the fragiligram, would seem to be of value in defining the clinico-haematological picture in clinical heart diseases and haemolytic anaemia.

Congenital erythrocyte enzyme deficiencies

Congenital hemolytic anemias resulting from PK, PFK, and G6PD enzyme deficiencies have been reported in domestic animals. Dogs with PFK deficiency may have episodes of intravascular hemolysis with hemoglobinuria in addition to a persistent compensated hemolytic anemia. Patients with mild G6PD deficiency are not anemic but may show increased susceptibility to oxidant-induced erythrocyte injury. Persistent methemoglobinemia has been reported in dogs and cats with methemoglobin reductase enzyme deficiency. Affected animals have cyanotic-appearing mucous membranes but show no or only mild clinical signs attributable to hypoxemia. Enzyme assays are usually done after acquired causes of hemolytic anemia and methemoglobinemia have been ruled out.