The aim should be to maintain strict phenylalanine control as long as possible. Patients should know that, even at this phenylalanine concentration, there is evidence that performance on specific decision making tasks may improve if phenylalanine concentrations are reduced. Given the major practical difficulties of treatment, especially in subjects with severe forms of phenylalanine hydroxylase deficiency, adolescents and young adults will have to make their own choices about their phenylalanine intake, having been appraised of the risks of high phenylalanine concentrations. In order to find a compromise between a good attitude to the burdensome diet and a normal personality development, we have to accept optimal serum phenylalanine levels for each patient, which in the individual case may not be ideal from a medical standpoint. As an alternative to continuing the low phenylalanine diet, a less restricted diet supplemented with all essential amino acids, except for phenylalanine, may be offered through adolescents into adulthood.
Monitoring requires a postal service for phenylalanine analysis.
Monitoring requires frequent contact between the family and those responsible for the child's care. Biochemical monitoring should continue on a weekly basis up to at least 4 years of age. After 4 years and up to 10 years the frequency of monitoring can be reduced to fortnightly and, thereafter, monthly. Blood phenylalanine should be measured by quantitative assay systems such as fluorometric, enzymatic, or by ion exchange chromatography. The Guthrie method should not be used for dietary monitoring.