[Use of computerized neuropsychological tests and of nuclear magnetic resonance spectroscopy in clinical assessment of adult patients with phenylketonuria].

Phenylketonuria is the most common inborn error of metabolism. Adult patients often discontinue dietary treatment and can subsequently develop serious brain dysfunction. Some of them, however, do not present any symptoms, despite long-term exposition to high blood phenylalanine concentration. As the extent of brain toxicity of hyperphenylalaninemia is not clear in adults, new diagnostic methods are needed to assess brain effects of hyperphenylalaninemia. The aim of the study was to evaluate the usefulness of magnetic resonance spectroscopy and of computerized neuropsychological tests for measurement of brain phenylalanine concentration and for early detection of hyperphenylalaninemia-related brain dysfunction. Assessment of sustained attention, working memory and inhibitive control was performed in a group of 50 adults with phenylketonuria by means of computerized CANTAB system. Additionally, in 40 patients, measurement of brain phenylalanine signal was done by means of magnetic resonance spectroscopy. The results were correlated with plasma phenylalanine concentrations. Worsening of neuropsychological efficiency as well as increase of brain phenylalanine concentration correlated with high levels of plasma phenylalanine. Interestingly, in two cases, despite high plasma phenylalanine concentration, low brain phenylalanine concentration was observed accompanied by good results of neuropsychological tests. This finding suggests presence of mechanisms limiting brain toxicity of hyperphenylalaninemia in some patients. It should be stressed, however, that such situation can be expected rarely, and is probably restricted to cases with moderate hyperphenylalaninemia. Combination of computerized neu- ropsychological tests and of magnetic resonance spectroscopy is a useful diagnostic method which could allow for careful individualization of dietary recommendations in selected patients with phenylketonuria.