Little research has been conducted to examine behavior and cognition in children with mild PKU/hyperphenylalanemia, but there is evidence of reductions in general intelligence (IQ) (Costello, 1994) and impairments in executive abilities (Diamond, 1994; Gassio, 2005) in this population. It is important to note that the phenylalanine levels of children with mild PKU are approximately equivalent to those of children with classical PKU whose phenylalanine levels have been managed through dietary control. In children with diet-treated PKU, impairments in behavior and cognition are well-documented, particularly in relation to executive abilities (Christ, 2006; White, 2001, 2002). Taken together, these findings suggest that children with mild PKU are at risk for behavioral and cognitive impairments, and it is possible that these impairments may be mitigated by lowering phenylalanine levels through treatment with Kuvan.