A test of the frontal-specificity hypothesis in the cognitive performance of adults with phenylketonuria

Twenty-two adults with phenylketonuria and 22 control participants matched for age, sex, and intelligence, performed three tasks known to be sensitive to the effects of frontal-lobe dysfunction, and three tasks sensitive to the effects of more posterior lesions. The most robust group differences were obtained with the frontal tasks, although some differences were also detected with the posterior tasks. In the participants with phenylketonuria, performance on the frontal tasks, but not the posterior tasks, was related to degree of phenylalanine elevation. The results are discussed in terms of the theory of dopamine depletion, frontal-lobe dysfunction, and cognitive performance in phenylketonuria.