Cognitive Development and Dietary Therapy in Phenylketonuric Children

Phenylketonuric children (now four years of age or older) were given intelligence and language tests to ascertain their present levels of cognitive functioning. These intellectual abilities were then evaluated in relation to the children's ages at the time diets low in phenylalanine were begun. The influence of distorting nontreatment factors, such as family level of intelligence and sociologic variation, was ascertained by computation of a multiple-regression equation analysis. Examination of the data revealed a consistent inverse relation between present intellectual ability and age of dietary inception. The children treated within one month after birth scored an average of 33 IQ points higher than those for whom treatment was initiated within their fourth and sixth years of life.