Glycogenosis in Dogs
Glycogen storage disease, also known as glycogenosis, is characterized by deficient or defective activity of the enzymes responsible for metabolizing glycogen in the body. It is a rare inherited disorder with various types, all of which lead to the accumulation of glycogen, the main carbohydrate storage material in the body which aids short term energy storage in cells by converting to glucose as the body needs it for metabolic requirements. This abnormal accumulation in the tissues can result in the enlargement and dysfunction of various organs, including the liver, heart, and kidneys.
There are four types of glycogenoses known to affect dogs, with certain species being more susceptible to some of these than others. Type I-a, more commonly known as von Gierke’s disease, occurs primarily in Maltese puppies; Type II, Pompe’s disease, occurs in Lapland dogs, usually beginning around six months of age; Type III, Cori’s disease, occurs in young female German Shepherds; and Type VII affects English Spring Spaniels aged two to nine.
Symptoms and Types
Type I-a, usually found in Maltese puppies, may result in failure to thrive, mental depression, low blood sugar (a condition known as hypoglycemia), and eventually death (or, to avoid symptoms, euthanasia) by sixty days of age.
Type II, usually found in Lapland dogs, is characterized by vomiting, progressive muscle weakness, and cardiac abnormalities. Death usually occurs before two years of age.
Type III, usually found in German Shepherds, results in depression, weakness, failure to grow, and mild hypoglycemia.
Type IV, found in English Spring Spaniels, results in hemolytic anemia, a condition in which red blood cells are destroyed, and hemoglobinuria, a condition in which the protein hemoglobin (which helps transport oxygen throughout the body) is abnormally highly concentrated in the patient’s urine.
The various forms of glycogenoses all result from some sort of deficiency in glucose-metabolizing enzymes in the body. The types are distinguished by the specific enzyme deficiency. In dogs, Type I-a results from deficiency of glucose-6-phosphatase, Type II from a deficiency of acid glucosidase, Type III from a deficiency of amylo-1 and 6-glucosidase, and Type VII from a deficiency of phosphofructokinase. Type IV, found in cats, results from a deficiency of the glycogen branching enzyme.
Diagnostic procedures will vary depending on the symptoms and suspected type of glycogen storage disease at hand. A tissue enzyme analysis and determination of glycogen levels can serve as a definitive diagnosis. Other tests may include urine analysis, genetic testing, and electrocardiography (ECG) to check the electrical output from the heart for changes.