PSYCHOLOGIC AND NEUROLOGIC STATUS OF DIET-TREATED PHENYLKETONURIC CHILDREN AND THEIR SIBLINGS

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Abstract
The neurologic status and intelligence of 8 phenylketonuric children treated with a phenylalanine-low diet were compared with that of 11 unaffected children and 3 untreated siblings. The mean intelligence of the treated children was significantly higher than that of their untreated siblings. This was true both for the two children given a special diet at 2 years of age and for those treated earlier, but the children treated before 6 months of age were significantly more intelligent than those treated at 2 years. The one child for whom treatment was begun at 1 year had an intelligence level within the range of the five who were treated earlier. Although intelligence was significantly higher in treated than in untreated children, and this was especially marked in the children treated early, all treated children were significantly less intelligent than their unaffected siblings. The loss in intelligence probably cannot be ascribed to poor chemical control, as treated children maintained phenylalanine levels within the normal range throughout treatment, with occasional brief exceptions. Neurologic findings paralleled the results of intelligence testing. There were no suggestive or positive findings among the unaffected children. Children treated early had some relatively minor findings, while children treated late and those who were untreated had a higher percentage and more marked signs of neurologic defect. Results of the present study considered together with results from other investigations, indicate that intelligence level, in phenylketonuric children, is a decelerating function of age. If this is true, the brain may be especially susceptible to damage in the first few weeks and months of life, and treatment should be instituted as early as possible.

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