Evaluation of Neuropsychiatric Function in Phenylketonuria: Psychometric Properties of the ADHD Rating Scale-IV and Adult ADHD Self-Report Scale Inattention Subscale in Phenylketonuria

Background: Previous qualitative research among adults and parents of children with phenylketonuria (PKU) has identified inattention as an important psychiatric aspect of this condition. The parent-reported ADHD Rating Scale-IV (ADHD RS-IV) and the Adult ADHD Self-Report Scale (ASRS) have been validated for measuring inattention symptoms in persons with attention-deficit/hyperactivity disorder (ADHD); however, their psychometric attributes for measuring PKU-related inattention have not been established. Objective: The primary objective of this investigation was to demonstrate the reliability, validity, and responsiveness of the ADHD RS-IV and ASRS inattention symptoms subscales in a randomized controlled trial of patients with PKU aged 8 years or older. Methods: A post hoc analysis investigated the psychometric properties (Rasch model fit, reliability, construct validity, and responsiveness) of the ADHD RS-IV and ASRS inattention subscales using data from a phase 3b, double-blind, placebo controlled clinical trial in those with PKU aged 8 years or older. Results: The Rasch results revealed good model fit, and reliability analyses revealed stong internal consistency reliability (alpha >= 0.87) and reproducibility (intraclass correlation coefficient >= 0.87) for both measures. Both inattention measures demonstrated the ability to discriminate between known groups (P < 0.001) created by the Clinical Global Impression-Severity scale. Correlations between the ADHD RS-IV and the ASRS with the Clinical Global Impression Severity scale and the age appropriate Behavior Rating Inventory of Executive Function Working Memory subscale were consistently moderate to strong (r >= 0.56). Similarly, results of the change score correlations were of moderate magnitude (r >= 0.43) for both measures when compared with changes over time in Behavior Rating Inventory of Executive Function Working Memory subscales. Conclusions: These findings of reliability, validity, and responsiveness of both the ADHD RS-IV and the ASRS inattention scales, in addition to content validation results, support their use for the assessment of inattention symptoms among persons with PKU aged 8 years or older in both clinical and research settings.