Metabolism refers to all processes in the body that break down and convert ingested substances to provide the energy and nutrients needed to sustain life. Foods, liquids, and drugs all generally undergo metabolic processes within the body. Many foods are complex materials that must be broken down into simpler substances, which in turn become “building blocks” for the body to use as needed. For example, protein is broken down into amino acids, which are used in several metabolic reactions. Enzymes made by the body are necessary for many metabolic processes. Whenever the function of an enzyme is affected, a metabolic disorder can develop. Metabolic disorders are important because they affect energy production or damage tissues. They may be genetic (inherited) or acquired. Acquired metabolic disorders are more common and significant.

Metabolic Storage Disorders

Metabolic storage disorders usually result from the body's inability to break down some substance because of the partial or complete lack of a certain enzyme. The substance can build up to a toxic level, or the body is unable to produce a substance that it needs. Although storage diseases are often widespread throughout the body, most clinical signs are due to the effects on the central nervous system. Metabolic storage disorders can be either genetic or acquired.

Genetic (inherited) storage diseases are named according to the specific metabolic byproduct that builds up in the body. Certain breeds of cats are more prone to certain storage diseases than others (see Metabolic Disorders of Cats: Breeds of Cats Prone to Genetic Storage Diseases). Kittens typically appear normal at birth, and clinical signs begin within a few weeks to months. These diseases are progressive and usually fatal because specific treatments do not exist.

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Breeds of Cats Prone to Genetic Storage Diseases Disease Breeds Ceroid lipofuscinosis Domestic shorthair Gangliosidoses Domestic shorthair Korat Siamese Globoid cell leuko-dystrophy (Krabbe's disease) Domestic shorthair Glycogenosis Domestic shorthair Norwegian forest cats Mannosidosis Domestic shorthair Persian Mucopolysacchari-dosis type I Domestic shorthair Korat Siamese Mucopolysacchari-dosis type IV Siamese Porphyria (associated with anemia) Domestic shorthair Siamese Sphingomyelinosis Domestic shorthair Siamese

Acquired storage diseases can be caused by eating plants that contain inhibitors of specific enzymes (see Poisoning: Plants Poisonous to Animals).

Production-related Metabolic Disorders

Some metabolic disorders are caused by an increased demand for a specific element or nutrient that has become deficient under certain conditions. For example, in hypoglycemia, the animal's metabolic reserves are unable to sustain sugar (or glucose) in the blood at a level needed for normal function. Likewise, in hypocalcemia, the level of calcium in the blood is too low. In some cases, dietary intake of a nutrient, such as calcium, is rapidly used up for an ongoing, high metabolic need, such as producing milk for kittens.

The difference between production-related metabolic diseases and nutritional deficiencies is often subtle. Typically, nutritional deficiencies are longterm conditions that develop gradually and can be corrected through dietary supplementation. Metabolic diseases usually begin suddenly and respond dramatically to administration of the deficient nutrient (although affected animals may need dietary supplements to avoid recurrence). Because production-related metabolic disorders are serious and develop suddenly, accurate and rapid diagnosis is essential. Ideally, diagnostic tests can be used to predict the chance of disease occurring so that either it can be prevented or preparations can be made for rapid treatment.

Last full review/revision July 2011 by George M. Barrington, DVM, PhD, DACVIM; David L. Evans, BVSc, PhD; Don A. Franco, DVM, MPH, DACVPM; Katharine F. Lunn, BVMS, MS, PhD, MRCVS, DACVIM; Donald C. Sawyer, DVM, PhD; Jean A. Hall, DVM, PhD, DACVIM; Sharon J. Spier, DVM, PhD, DACVIM; Ivan W. Caple, BVSc, PhD, MACVSc, MRCVS