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

ABSTRACT

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.