Inborn Errors of Metabolism Health Article

Inborn Errors of Metabolism

Inborn errors of metabolism are inherited disorders in which the body cannot metabolize the components of food (carbohydrates, proteins, and fats). Metabolism is the biochemical process that changes food components into energy and other required molecules. These disorders may be caused by the altered activity of essential enzymes, deficiencies of the substances that activate the enzymes, or faulty transport compounds. Metabolic disorders can be devastating if appropriate treatment is not initiated promptly and monitored frequently.

Inborn errors of metabolism often require diet changes, with the type and extent of the changes dependant on the specific metabolic disorder. The particular enzyme absence or inactivity for each inborn error of metabolism dictates which components are restricted and which are supplemented. Registered dietitians and physicians can help an individual assess the diet changes needed for each disease. The goals of nutrition therapy are to correct the metabolic imbalance and promote growth and development by providing adequate nutrition, while also restricting (or supplementing) one or more nutrients or dietary components. Additional goals in some disorders include reducing the risk of brain damage, other organ damage, episodes of metabolic crisis and coma, and even death. These restrictions and supplementations are specific for each disorder, and they may include the restriction of total fats, simple sugars, or total carbohydrates.

Listed below are several of the metabolic disorders that respond to nutrition therapy. The appropriate dietary restrictions and modifications that are necessary for treatment are also listed.

Disorders of Amino Acid Metabolism

Phenylketonuria (PKU) is the most common disorder of amino acid metabolism. In this disorder the body cannot use the amino acid phenylalanine normally, and excess amounts build up in the blood. If untreated, PKU can cause mental retardation, seizures, behavior problems, and eczema. With treatment, persons with PKU have normal development and intelligence. The treatment for PKU consists of a special phenylalanine-restricted diet designed to maintain blood phenylalanine levels within an acceptable range. Medical formulas and foods, which do not contain phenylalanine, are used to provide the necessary intake of protein and other nutrients. Foods containing natural protein are prescribed in limited amounts to meet the body's requirement for phenylalanine, without providing too much.

Maple syrup urine disease (MSUD) is a disorder in which the body is unable to use the amino acids isoleucine, leucine, and valine in a normal way. Excessive amounts of these amino acids and their metabolites will build up in the blood and spill into the urine and perspiration, giving them the odor of maple syrup (which is how this disorder got its name). An untreated infant with MSUD may have some or all of the following symptoms: difficulty breathing, sleepiness, vomiting, irregular muscle movement, seizures, or coma, and the disease can cause death. Basic treatment involves restricting foods and infant formula that contain leucine, isoleucine, and valine. Medical formulas and foods, which contain very small amounts of leucine, isoleucine, and valine, are used to provide the necessary intake of protein and other nutrients.