Brain phenylalanine concentration in the management of adults with phenylketonuria.

Diagnosis by newborn screening and the implementation of a phenylalanine-restricted diet have resulted in normal neurological development in approximately 10 000 persons with phenylketonuria (PKU) in the United States. While it is accepted that a phenylalanine-restricted diet is necessary in childhood, the recommended concentration of phenylalanine in the blood varies. Clinicians now must make recommendations for adults with PKU who probably tolerate higher levels of phenylalanine than children. This factor, quality of life issues, the expense of the diet, and varying genetic and socio-economic backgrounds, make the choice of dietary recommendations difficult.