The results give evidence that even dietary treated children with PKU were suffering from impaired attentional control mechanisms in spite of a normal IQ. The deficits might be the result of impaired frontal lobe functions.

In a retrospective study, 34 early treated, normally intelligent adolescents with phenylketonuria (PKU) and their parents were tested with several psychometric personality inventories and self-developed questionaires concerning their psychosocial situation and their disease- and diet-specific knowledge. Results show that the patients are characterized by less autonomy, a more negative evaluation of their scholastic ability, less achievement motivation, low frustration tolerance, more negative self description, less extraversion and impulsiveness, a feeling of not being quite healthy, more grave and a higher level of dependency from their families. The patients saw their whole social situation as being distinctly restricted. Their knowledge concerning disease and diet was alarmingly poor and the majority had great difficulties in managing the diet satisfactorily without parental help. Up to the age of 15 years the serum phenylalanine levels were persistently above the desired range.

Twenty early treated, normal intelligent patients (IQ: mean 101.4, SD 10.0; age: mean 10.11, SD 1.3 years) with classical phenylketonuria and 20 age-, sex- and IQ-matched healthy controls were investigated for neurological outcome, especially with regard to fine motor ability using the motor performance task ("Motorische Leistungsserie"). No pathological findings were seen on clinical neurological examination. The patient group had significantly poorer results in a concentration task (Test-d-2) as well as in some subtests of the motor performance task. Patients had difficulties in tasks which needed speed and precision of arm-hand-finger movements. High serum phenylalanine concentrations were significantly correlated with these deficiencies in fine motor ability. Our data demonstrated mild neurological impairment even in early and relatively strictly treated patients with phenylketonuria.

In adolescents and adults with PKU, blood phenylalanine levels above 10mg/dl are generally associated with white matter changes in MRI. The grade of these changes is correlated to most recent blood phenylalanine levels. Based on studies using T2 relaxometry the MRI changes seem to be the consequence of a reversible dysmyelination. The clinical relevance of these white matter changes remains unclear as the extent of MRI alterations did not correlate with IQ, neurological and electrophysiological deficits of the patients. The intracerebral phenylalanine concentration as measured by protonspectroscopy amounts to about 50% of blood phenylalanine concentrations. Preliminary data indicate that brain phenylalanine levels remain constant if blood concentrations exceed 20 mg/dl. This might be of clinical relevance for the treatment of adolescent and adult PKU patients.

In a retrospective study, 34 treated adolescents with phenylketonuria and their relatives were tested with scale 2 of the Culture Fair Intelligence Test (CFT20) and self-developed questionnaire concerning their development in school. The patients also filled in the Anxiety Questionnaire for Children. With an IQ of 93.6, the patients reached a normal mean intellectual performance but this was significantly below the mean IQ of the general population (100, p < 0.01), the IQ of their mothers (98.2, p < 0.05), their fathers (105.4, p < 0.05) and their siblings (110.3, p < 0.05). The patients' IQs correlated significantly with the IQs of their mothers, the socio-economic status of their families, the quality of dietary control since birth and the serum phenylalanine concentration at the moment of testing. With respect to age at which the patients started school, type of school attended and number of school years which had to be repeated, there were no significant differences between the patients and their siblings. The patients did not display a markedly higher degree of general anxiety, nervousness at examination time or a greater reluctance to attend school.