SUSTAINED ATTENTION IN ADULT PHENYLKETONURIA - THE INFLUENCE OF THE CONCURRENT PHENYLALANINE-BLOOD-LEVEL

The effect of concurrent phenylalanine levels (Phe-level) on sustained attention was tested in a group of 19 early treated adult PKU patient s. Mean age was 20.5 years; WAIS IQs were in the normal range (M = 109 .3). Phe-levels were manipulated in a high-low-high design by reintrod uction of a strict phenylalanine-reduced diet for 4 to 5 weeks between test time 1 and 2 and returning to usual diet between test time 2 and 3. A control group of 20 healthy subjects, mean age 20.7 years was te sted twice. Results of a sustained attention task are presented. In ad ult PKU patients with high concurrent Phe-Ievels, sustained attention is significantly impaired and reaction times are prolonged. In the low Phe-level condition, performance improved significantly. Nevertheless , the PKU group did not reach the level of performance of the control group. Results are not influenced by IQ and suggest a sustained attent ion deficit in adult PKU patients that varies according to the concurr ent Phe-level. The partial reversibility of the deficits provides supp ort for the hypothesis that biochemical mechanisms rather than structu ral changes of the brain underlie the relationship between concurrent Phe-level and sustained attention.