Patients with the BH 4 cofactor deficiency have more severe neurologic problems that are not corrected completely by dietary reduction of phenylalanine. The learning disabilities in patients with PKU who are treated adequately may result from reduced production of neurotransmitters as a result of deficient tyrosine transport across the neuronal cell membranes. Psychological problems, including agoraphobia and other disorders, have been reported in individuals both on and off dietary treatment. PKU is common in Caucasians and Asians and is rare in black people. Untreated maternal PKU increases the risk for developmental problems in offspring.
Most patients appear normal at birth.
In untreated adult patients who stop dietary treatment, neurologic dysfunction may occur. Other causes of PKU include BH 4 deficiency and DHPR deficiency. PKU displays a marked genotypic heterogeneity, both within populations and between different populations. Perform screening on blood samples during the first week of life. Perform urinalysis of biopterin and neoptrins to exclude defects of biopterin synthesis or recycling.