Inborn errors of metabolism

Alternative names:

Human hereditary biochemical disorders

Recommendations:

Many inborn errors of metabolism are untreatable. Some inborn errors of metabolism require dietary changes, restrictions of certain nutrients, extremely high dosages of certain nutrients or combinations of all of these. The type and extent of the change depends on the specific metabolic error. Registered dietitians and physicians can help with the diet modifications needed for each disease.

The following are a few examples of the many inborn errors of metabolism which require dietary changes:


Fructose intolerance:

• Fructose intolerance and fructosemia. Genetic disorders in the breakdown and metabolism of the simple sugar fructose. It is potentially life threatening but may be treated by diet changes - generally restricting all fructose containing foods.
• Food sources of fructose include: fruits, fruit juices, sucrose (all sugars--cane, beet, white, brown, etc), corn syrups, honey, sorbitol, levulose, invert sugar, some vegetables and starches.
• It is recommended that all fructose be avoided in the diet. The severity of the restriction depends on individual tolerance. Sugar and fructose are found in many foods, making the diet difficult to follow, especially for young children who, by nature, are attracted to sweets.

Galactosemia:

• Galactosemia is a genetic (inherited) disorder resulting in the decreased transformation of the simple sugar galactose to glucose. Elevated levels of galactose can result in cataracts, enlarged liver, enlarged spleen and mental retardation. Breast milk, cow's milk and the milk of other mammals contains lactose or milk sugar. Lactose is made up of one molecule of glucose and one molecule of galactose, both of which are simple sugars. An individual with galactosemia is unable to convert galactose to glucose. Galactose subsequently builds up in the body. Since galactose is toxic it causes damage that results in mental retardation and the other findings. Since galactose is found only in milk and nowhere else in nature, completely restricting milk from the diet will prevent the damaging effects of galactosemia.
• Food sources of galactose include: mammalian milks, dairy products and foods containing dairy products.
• Milk and milk containing products must be avoided, including yogurt, cheese, ice cream. Galactose-free and lactose-free milk substitutes and foods should be used. Traces of galactose may be found in other plants but are insufficient to cause problems: sugar beets, gums, seaweed, flaxseed, mucilage, some vegetables, etc.
• Women who carry the genetic trait should also follow the diet since galactose may cause mental retardation in the fetus. Contact a Registered Dietitian for complete information on a galactose free diet.

Maple sugar urine disease (MSUD):

• A rare genetic disorder in the breakdown of the branch chain amino acids valine, leucine, and isoleucine. Typically the disease is found shortly after birth and is characterized by urine that smells like maple syrup, vomiting, refusal to eat, and increased reflexes. If left untreated, life-threatening neurological damage may result.
• Treatment includes a special diet with restriction of protein intake to reduce levels of leucine, isoleucine and valine. Special formulas are available that contain all of the important amino acids except leucine, isoleucine and valine. Strict dietary compliance is necessary to prevent neurological damage. This requires close supervision by a registered dietitian or physician, and cooperation by parent(s).

Phenylketonuria (PKU):

• Phenylketonuria is a rare genetic disorder in the degradation of dietary phenylalanine that can result in severe progressive mental retardation if left untreated. Most states require blood or urine testing for PKU in all newborns. In this condition, phenylalanine, an amino acid, cannot be used and regulated properly. Serum phenylalanine levels rise causing damage to the brain, liver and other organs.
• A low phenylalanine diet is the normal treatment. Strict compliance to the diet is necessary to reduce or prevent mental retardation. Special phenylalanine-free formulas are available for infants with this condition. The diet is extremely restrictive and requires close supervision by a registered dietitian or physician, and close cooperation of the parent(s) and child.