Outcomes in mild hyperphenylalaninemia: a comparison with PKU and healthy controls across cognition, behaviour, and quality of life.

Aims: Considering the cognitive, behavioural and quality of life (QoL) consequences of high phenylalanine levels in early treated phenylketonuria (PKU), this study examined whether monitoring and active management of individuals with the mild form of the condition hyperphenylalaninemia (HPA) would be advisable.

Method: Six individuals (aged 6 to 15) with untreated HPA were compared with six age and gender matches with PKU, and six healthy controls on the Wechsler Intelligence Scale for Children, 5th edition; Wechsler Individual Achievement Test, 2nd edition; Trail-Making test; Contingency Naming Test; and Oral Fluency test. Self- and parent-report rating scales administered included the Conners Comprehensive Behavior Rating Scales; Behavior Rating Inventory of Executive Function, 2nd edition; the Pediatric Quality of Life Inventory, and the Phenylketonuria Quality of Life (PKU group only) questionnaires.

Results: Early treated PKU participants demonstrated normal intelligence, pointing to the efficacy of dietary management. Quality of life and behavioural difficulties were observed including more severe externalising problems. HPA participants showed normal ability, including executive ability. Power was limited by the small sample.

Conclusion: This was the first study of the New Zealand population with HPA. While there was insufficient evidence to warrant treatment, there was also insufficient evidence to safely exclude the presence of cognitive impairment.