Preliminary neuropsychological test results

Abstract

A series of information processing tasks was administered to 22 PKU children aged 8.5 years who had been under dietary treatment since birth as well as to 20 controls of the same age. This contribution presents the results of two tasks from this series: a continuous performance task and a calculation task. The continuous performance task revealed a sustained attention deficit in the PKU group. In the calculation task the PKU children were slower than the controls and this difference increased with task difficulty. When the PKU sample was divided in two groups (above and below the median value of the concurrent plasma Phe level), the high Phe level group performed much worse in comparison to the low Phe level group. The latter group actually matched performance level of the controls. This could be observed for both tasks. The serum Phe level, assessed since birth over 6 month periods, correlated highly with task performance. As regards sustained attention, the Phe level measured during the 2 years preceeding test administration appeared to be an even better predictor for task performance than the concurrent Phe level, a finding which seems to underline the chronic effect of Phe on basic attention mechanisms. The results so far seem to stress the value of well-controlled dietary restrictions.

Information processing in patients with early and continuously-treated phenylketonuria

“…As this difference was independent of the stimulus interval manipulation it could not be inter preted in terms of an inability to preset a response. Although these findings may seem inconsistent with the results of earlier studies which showed that PKU pa tients perform more slowly and/or less accurately than controls in a variety of information processing tasks [ [29] demonstrated that differences in task performance between PKU patients and controls could be attributed solely to a group of pa tients with Phe levels > 600 |Ltmol/i whereas the perfor mance of patients with Phe-levels < 600 jLimol/1 actually matched that of the controls. Our sample of PKU patients had been continuously maintained on a well-controlled Phe-restricted diet, resulting in average Phe levels that were low compared to the levels generally mentioned in the literature [1,3,5,6,7,14].…”

“…Our sample of PKU patients had been continuously maintained on a well-controlled Phe-restricted diet, resulting in average Phe levels that were low compared to the levels generally mentioned in the literature [1,3,5,6,7,14]. Although the number of patients in our sample with Phe levels > 600 (.Lmol/1 was too small to permit a comparison between patients with "good" and patients with "poor" control (as was done by de Sonneville et al [29]), it seems reasonable to assume that the low Phe levels found in our patient group have in deed contributed to the absence of group differences in the present study. These low Phe levels in combination with the small range of the Phe levels, may also have pre vented strong correlations between biochemical data and performance measures.…”

“…For the same periods we computed the percentage of Phe levels that were outside the Dutch target range, that is, the percentage of Phe levels below 200 |imol/l and the percentage of Phe levels above 480 jimol/I. In addition, we computed the percentage of Phe levels considered too low [25] (Phe < 120 |imol/l) and the percentage of Phe levels above 600 ixmol/1 [29] (see Table 2). …”

“…All PKU pa tients had been treated early and continuously, aiming at currently recommended [16] Phe levels between 200 and 480 jnmol/1. Since previous reports have shown that the speed of performance of PKU patients depends critically on their Phe levels [28,29], information processing effi ciency was examined in relationship to the patients' Phe level. In addition, data on intelligence level and task ori ented behaviour were obtained for both groups to allow for a more complete evaluation of the effectiveness of stricter dietary treatment.…”

Neuropsychological and biochemical investigations in heterozygotes for phenylketonuria during ingestion of high dose aspartame (a sweetener containing phenylalanine)

“…A primary reason for selecting this battery was that it is sensitive to changes in phe concentrations in children (de Sonneville et al 1990;Schmidt et al 1992), and in adults (Pietz et al 1993). It has been demonstrated in PKU patients that a higher phe concentration parallels a slower performance in the sustained attention and divided attention tasks (de Sonneville et al 1990;Schmidt et al 1992).…”