Storage diseases and inborn errors of metabolism are classified as either genetic or acquired. These diseases are characterized by the accumulation or storage of specific lysosomal enzyme substrates or byproducts within cells because of partial or complete deficiency of those enzymes. Although lysosomal storage diseases are often widespread throughout the body, most clinical signs are due to the effects on the CNS.
Genetic Storage Disease in Animals
Genetic storage diseases are named according to the specific metabolic byproduct that accumulates in the lysosomes. Animals are typically apparently normal at birth, then manifest clinical signs within the first weeks to months of life. These diseases are progressive and usually fatal, given that specific treatments do not exist.
In small animals, the gangliosidoses (GM1 gangliosidosis and GM2 gangliosidosis) occur in Siamese, Korat, and domestic cats and in Beagle crosses, German Shorthaired Pointers, Japanese Spaniels, Portuguese Water Dogs, English Springer Spaniels, Alaskan Huskies, and Shiba Inus. Sphingomyelinosis occurs in German Shepherd Dogs and Poodles and in Siamese and domestic shorthair cats. Glucocerebrosidosis occurs in Australian Silky Terriers and Dalmatians. Ceroid lipofuscinosis occurs in English Setters, Cocker Spaniels, Dachshunds, Chihuahuas, Salukis, Border Collies, and domestic cats. Mannosidosis occurs in Persian and domestic cats. Glycogenosis occurs in Silky Terriers and in domestic shorthaired and Norwegian forest cats. Globoid cell leukodystrophy (Krabbe disease) occurs in Cairn Terriers, West Highland White Terriers, Beagles, Bluetick Hounds, Poodles, and domestic shorthair cats. Mucopolysaccharidosis type I occurs in Siamese, Korat, and domestic shorthair cats, whereas type IV occurs in Siamese cats.
In dogs, mucopolysaccharidosis occurs in Miniature Pinschers, Plott Hounds, Rottweilers, Labrador Retrievers, Wirehaired Dachshunds, New Zealand Huntaways, Schipperkes, Welsh Corgis, Miniature Schnauzers, Chesapeake Bay Retrievers, German Shepherd Dogs, Rat Terriers, and mixed-breed dogs and is associated with lameness. Diseases associated with decreased RBC survival and anemia include pyruvate kinase deficiency in Basenjis, Beagles, and West Highland White and Cairn Terriers; phosphofructokinase deficiency in English Springer and American Cocker Spaniels; and porphyria in Siamese and domestic shorthair cats.
In large animals, alpha-mannosidosis occurs in Angus, Murray Grey, Simmental, Galloway, and Holstein cattle. Beta-mannosidosis occurs in Saler cattle and Nubian and Nubian-cross goats. Generalized glycogenosis (GM1) occurs in Holstein cattle and Suffolk sheep. Generalized glycogenosis (GM2) occurs in Shorthorn and Brahman cattle, and in pigs. Globoid cell leukodystrophy occurs in polled Dorset sheep.
Other identified diseases that are associated with neurologic signs and appear to be inherited include neuronal lipodystrophy in Angus and Beefmaster cattle, shaker calf syndrome of horned Hereford cattle, maple syrup urine disease of Hereford and polled Shorthorn cattle, and hereditary neuraxial edema of polled and horned Hereford and Hereford-Friesian cross cattle. There have been no reports of lysosomal storage diseases in horses; however, inherited diseases manifested by neurologic signs include inherited myoclonus of Peruvian Paso foals and congenital encephalomyelopathy in Quarter Horses.
Other inherited diseases that involve basic errors of metabolism in various tissues include goiter of sheep and goats, inherited parakeratosis (edema disease) of cattle, osteogenesis imperfecta of sheep and cattle, and possibly cardiomyopathy of cattle, the hypotrichoses, baldy calves, photosensitization of sheep, dermatosis vegetans of pigs and porcine stress syndrome, dermatosparaxia and Ehlers-Danlos syndrome of cattle, hemochromatosis of cattle, and Marfan syndrome in cattle. Many other inherited defects, especially those based on abnormal growth of collagen, cartilage, and bone, also are likely to have basic errors of metabolism of structural tissues. Many disorders of metabolism have been described involving dysfunctions of the immune system.
Acquired Storage Disease in Animals
Acquired storage diseases are due to ingestion of plants that contain inhibitors of specific lysosomal catabolic enzymes. Chronic ingestion of locoweed plants (Astragalus or Oxytropis spp) results in an acquired neurologic storage disease. Several toxic components, including locoine, swainsonine n-oxide, and indolizidine alkaloids, interfere with alpha-mannosidase activity. Horses are most susceptible to intoxication; however, cattle, sheep, and goats can also be affected. (Also see Treatment and Control.)
