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.

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The intellectual, neurological, and neuropsychological outcome of patients with non-phenylketonuric-hyperphenylalaninaemia (PKU-HPA) (serum phenylalanine levels under free diet < 600 mumol/l) has not been systematically studied so far. We therefore tested 28 patients (mean age = 21.8, SD = 4.2 years) for IQ (WAIS-R/WISC-R), school performance, job career, clinical neurological examination, fine motor performance (motor performance task), and selective and sustained attention (stroop task, Dot Pattern Exercise from the Sonneville visual attention task). In addition, cranial MRI (1.5 T unit) was obtained in 10 of these patients. Clinical-neurological examination revealed no significant abnormalities in the non-PKU-HPA patients. They also had a normal IQ (mean = 101.9, SD = 13.6). Compared to their healthy siblings, they attended a normal school and had a normal job career. The motor performance task revealed no deficits in fine motor abilities. The patients performed normally in the stroop task and the dot pattern exercise. Their MRIs were normal. Our results indicate that patients with non-PKU-HPA are not at risk for developing intellectual, neurological, and neuropsychological impairment, as described for patients with treated mild or classical phenylketonuria. From this point of view a dietary treatment is not necessary in patients with hyperphenylalaninaemia.

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