In untreated PKU patients, abnormally high phenylalanine levels in the blood and brain can produce nerve cells with deformed axons and dendrites and cause imperfections in the myelin sheath referred to as hypomyelination and demylenation.
Treatment consists of avoiding phenylalanine supplements, diet products containing aspartame (which also contain phenylalanine), and phenylalanine-rich foods such as cocoa powder, gelatin, and many meat, dairy and higher protein foods.
The amount of natural foods allowed in a diet can be adjusted to ensure that the level of phenylalanine in the blood is kept within a safe range-2 to 6 mg/dL before 12 years of age and 2 to 15 mg/dL for PKU patients over 12 years old.
If the initial PKU test produces a positive result, then follow-up tests are performed to confirm the diagnosis and to determine if the elevated phenylalanine levels may be caused by some medical condition other than PKU.
Ideally, school-age children with PKU should be taught to assume responsibility for managing their diets, recording food intake, and for performing simple blood tests to monitor their phenylalanine levels.