Late diagnoses usually are made during amino acid analysis of individuals who are developmentally abnormal. A qualified laboratory should measure plasma phenylalanine and tyrosine. A qualified laboratory should perform urine analysis of biopterin and neoptrins in order to rule out defects of biopterin synthesis or recycling. Areas of demyelination commonly are found. Most patients are treated in a specialty metabolic clinic, usually under the auspices of a genetics or pediatric endocrinology clinic.
Treatment consists of dietary restriction of phenylalanine with tyrosine supplementation.
The extent of phenylalanine restriction necessary for normal outcome remains controversial. Phenylalanine levels are followed at regular intervals, from 1-2 times weekly in neonates to once per month in older children and adults. Some adults with untreated PKU who are mentally retarded adults may show improvement in behavior and physical manifestations when treated with a phenylalanine-restricted diet. A psychologist should perform developmental testing at regular intervals. Whenever possible, the patient and parents should work with a nutritionist experienced in PKU, usually as part of a PKU or metabolic clinic.