NEUROPSYCHOLOGICAL EFFECTS OF SUBSEQUENT EXPOSURE TO PHENYLALANINE INADOLESCENTS AND YOUNG-ADULTS WITH EARLY-TREATED PHENYLKETONURIA

Severe mental handicap in phenylketonuria (PKU) can be prevented if di etary treatment is implemented at birth. Controversy remains about the optimum age for terminating treatment. A group of adolescents and you ng adults with PKU from the West of Scotland Register was identified w hich had received early treatment, been well-controlled on diet, cease d treatment at 10 years old and subsequently were hyperphenylalaninaem ic for 3 years or more. They were given a battery of neuropsychologica l tests and their results were compared with those of on-diet subjects with PKU and normal controls. The findings generally supported the vi ew that dietary cessation at age 10 is sufficient to prevent a substan tial reduction of cognitive and motor ability, and that the central ne rvous system is probably mature enough to withstand the toxic effects of high blood phenylalanine by then. However, there were minor indicat ions, in keeping with Welsh et al.'s hypothesis [:M.C. Welsh, B.F. Pen nington, S. Ozonoff, B. Rouse & E.R.B. McCabe (1990) Neuropsychology o f early-treated phenylketonuria: specific executive function deficits. Child Development 61, 1697-713], that subtle intellectual deficiencie s might arise both during and after treatment, possibly in the realm o f frontal-executive functions.