The use of d2 and benton tests for assessment of attention deficits and visual memory in teenagers with phenylketonuria

Abstract

Hyperphenylalaninemia-related, subtle deficits of attention and of working memory are often reported in adolescents with phenylketonuria. Focused neuropsychological tests can be used to detect such deficits and to confirm the presence of poor metabolic control in the periods between routine blood phenylalanine tests, which are rarely performed in many patients from this age group due to their low treatment adherence. We assessed the practical value of the d2 test of attention and of the Benton visual retention test for identification of teenagers, who have a high risk of brain dysfunction due to hyperphenylalaninemia. We analyzed the correlation between neuropsychological test scores achieved by 30 patients and their blood phenylalanine profiles since the neonatal period. We observed strong correlation between the Concentration Performance scores on the d2 test and the quality of metabolic control within last month prior to the follow-up visit in the outpatient clinic (r = −0.72; p = 0.0003). The mean z-score was significantly higher in patients with good metabolic control than in those with poorly controlled hyperphenylalaninemia (0.44 vs. −1.12; p = 0.00002). On contrary, the results of the Benton visual retention test did not correlate significantly with the individual blood phenylalanine profiles. We believe that neuropsychological assessment should be used in adolescents with phenylketonuria on a regular basis in order to increase the self-awareness in these patients and, consequently, to increase their treatment adherence and safety. The d2 test can be effectively used for detection of attention deficits and seems to be a valuable supplementary procedure for routine follow-up.