This is known as benign hyperphenylalaninemia . A special diet is not usually necessary. Once the diagnosis of classic PKU is made, the child should be started on a special formula that is low in phenylalanine. Once the diagnosis of classic PKU is made, the child should be started on a special formula that is low in phenylalanine. Because phenylalanine is an essential amino acid, the diet is designed to provide just enough of this amino acid for normal growth and development.
Dietary control is absolutely necessary for normal brain development.
Once the brain is fully developed, some specialists will also the child to relax the dietary restrictions after age 6 years. However, older patients who eat excessive amounts of phenylalanine will report decreased ability to concentrate and a decline in school performance if the diet is abandoned. For children with other types of PKU, dietary control alone is usually not successful and other therapies must be tried. The geneticist can also counsel the parents on the risk of having another child with the disease as well. Development is tracked closely as are blood levels of phenylalanine.