Summary of findings from the United States Collaborative Study of children treated for phenylketonuria

Abstract

The Collaborative Study of children treated for phenylketonuria (PKUCS) was conducted to investigate prospectively the effects of dietary restriction of phenylalanine on the growth and development of these children. Patients with classic phenylketonuria were identified by newborn screening and began treatment shortly thereafter. All were given the restricted diet until age 6 years, when half were randomly assigned to continue and half to discontinue dietary therapy. By age 10 years, 35% had deviated from randomization. The effects of diagnostic, treatment, and psychosocial factors on cognitive test scores were evaluated through 12 years of age. After controlling for parent IQ, significant correlations were noted between various measures of control of blood phenylalanine and their scores on intelligence, reading, spelling and behavior tests, but not for arithmetic or language scores. Bender Gestalt test scores were related to phenylalanine level at the time of testing, but not to early treatment history. These findings strongly support the importance of early initiation of dietary treatment and continuation of therapy throughout childhood.