Factors Influencing Verbal Intelligence and Spoken Language in Children with Phenylketonuria.

OBJECTIVE To determine verbal intelligence and spoken language of children with phenylketonuria and to study the effect of age at diagnosis and phenylalanine plasma level on these abilities. DESIGN Cross-sectional. SETTING Children with phenylketonuria were recruited from pediatric hospitals in 2012. Normal control subjects were recruited from kindergartens in Tehran. PARTICIPANTS 30 phenylketonuria and 42 control subjects aged 4-6.5 years. Skills were compared between 3 phenylketonuria groups categorized by age at diagnosis/treatment, and between the phenylketonuria and control groups. MAIN OUTCOME MEASURES Scores on Wechsler Preschool and Primary Scale of Intelligence for verbal and total intelligence, and Test of Language Development-Primary, third edition for spoken language, listening, speaking, semantics, syntax, and organization. RESULTS The performance of control subjects was significantly better than that of early-treated subjects for all composite quotients from Test of Language Development and verbal intelligence (P<0.001). Early-treated subjects scored significantly higher than the two groups of late-treated subjects for spoken language (P=0.01), speaking (P=0.04), syntax (P=0.02), and verbal intelligence (P=0.019). There was a negative correlation between phenylalanine level and verbal intelligence (r=-0.79) in early-treated subjects and between phenylalanine level and spoken language (r=-0.71), organization (r=-0.82) and semantics (r=-0.82) for late-treated subjects diagnosed before the age one year. CONCLUSION The study confirmed that diagnosis of newborns and control of blood phenylalanine concentration improves verbal intelligence and spoken language scores in phenylketonuria subjects.