Developmental Timing of Exposure to Elevated Levels of Phenylalanine is Associated With ADHD Symptom Expression

This study addresses attention deficit hyperactivity disorder (ADHD), with a focus on how the timing of a known biological insult affects ADHD symptom expression. The sample consists of children exposed to elevated levels of phenylalanine, either postnatally as in Phenylketonuria (PKU; n D 46) or prenatally as in Maternal PKU (MPKU; n D 15). Non-hyperphenylalaninemic siblings of children with PKU (n D 18) serve as controls. Results indicate that elevated levels of phenylalanine are associated with ADHD symptoms. The manifestations of the symptom expression are dependent on exposure timing: prenatal exposure is associated with a higher likelihood of expressing hyperactive/ impulsive symptoms and postnatal exposure is associated with a higher likelihood of expressing inattentive symptoms. This toxicity is dose-dependent and higher levels of phenylalanine appear more detrimental.