In phenylketonuria (PKU), a defect in the liver enzyme prevents the conversion of the protein called phenylalanine into a useful form. Instead, the phenylalanine builds up in the bloodstream and hampers normal brain development. If left untreated, a child with PKU will suffer mental retardation by the end of his or her first year, with the first signs of intellectual delay exhibited by six or seven months of age. Walking and talking are delayed; in some cases the child never accomplishes either. The retardation worsens until the age of six when brain growth is typically complete. One-third of untreated PKU children will suffer seizures.
Throughout most of the United States, a Guthrie PKU test is required for all newborns. It is conducted on blood pricked from the baby's heel. If a particular hospital does not routinely conduct this test, parents should request that their child be tested. One in every 16,000 infants is born with PKU. The incidence is highest among those of northern European descent; the lowest incidence occurs among those of Jewish, Asian, or African descents. The disease is equally distributed among boys and girls.
PKU is treated by a low-protein diet. Inattention to the dietary restrictions can result in behavioral disturbances and/or learning disabilities . The newborn diagnosed with PKU is immediately placed on a low-protein milk substitute. Recent studies suggest that PKU babies can be fed a controlled amount of breast milk. Once the child is ready for solid foods, the diet is primarily vegetarian. Meat, fish, poultry, eggs, and cheeses are prohibited. Protein substitutes are now available for peanut butter, breads, and breakfast foods such as waffles and pancakes. As yet, most private health insurance plans and public health programs do not reimburse for these protein substitutes with the exception of infant formula.
Affected children usually visit a PKU clinic every two to four months for a physical, a blood test, and a diet adjustment, if necessary. When the child enters school, adherence to the diet can be frustrating for both the parents and the child. Parents should involve the child in devising the food he or she wants in a way that fits the dietary restrictions. For example, hamburgers can be made with a low-protein mushroom mixture in the place of beef.
Medical experts differ on their recommendations for how long the low-protein diet is necessary. Some believe that once the myelin coating of the brain is complete at about five years of age, a regular diet is safe. Others recommend that the diet be followed throughout life. Many children shed the diet when they reach their teens. However, women of child-bearing age who are planning to become pregnant should maintain a low-protein diet. The high level of phenylalanine in their bloodstreams could have serious consequences for their unborn children. Although the recessive hereditary nature of the disease will prevent the child from having PKU, he or she is at high risk for mental retardation, microcephaly (an abnormally small head), low birth weight, and congenital heart disease if the mother does not regulate her protein intake.
One out of every 50 adults is a PKU carrier. Genetic testing can determine if the prospective parents are carriers. A prenatal PKU test is currently under development.
Further Reading
For Your Information
Periodicals
- Magol, Marsha. "Food for Thought: Helping Your Child on a Special Diet Eat Right." The Exceptional Parent 25, August 1995, no. 8, p. 52.
Gale Encyclopedia of Childhood & Adolescence. Gale Research, 1998.
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