Background: In phenylketonuria (PKU) a phenylalanine restricted diet during the first years of life can prevent the development of severe cognitive damage.
Objective: Could neuropsychological or neurological changes occur in a 20-year-old patient with PKU (diagnosed early and treated until the age of 8 years) after 12 years of normal nutrition and if so, can these changes be counteracted by reinstitution of a low phenylalanine diet?
Methods: Psychological (intelligence, attention), neurophysiological (evoked potentials) and neuroradiological examination (magnetic resonance tomography [MRT] of the brain) were performed before and after one year of treatment with a diet low in phenylalanine.
Results: During the reinstitution of dietary therapy we observed significant improvements in attentiveness (percentage increase of 30), whereas intelligence subtests remained stable, a reduction in hyperreflexia, shortening of the latencies of the evoked potentials and a decrease in periventricular pathological signal alterations as evaluated by MRT.
Conclusions: The reintroduction of a diet low in phenylalanine improved psychological and neurological symptoms in this PKU patient. We recommend a constant low-phenylalanine diet throughout life in patients with PKU.