EVALUATION OF PSYCHOMETRIC PROPERTIES OF THE PHENYLKETONURIA-SYMPTOM SEVERITY AND IMPACTS SCALE (PKU-SSIS) IN ADOLESCENTS WITH PKU
Author(s)
Hafiz Oko-osi, MS, PharmD1, Amy Howerter, PhD2, Ibrahim Alfayoumi, MS2, Tanu Bhargava, PhD2, Kate Delaney, BA, CSP1, Karon Cook, PhD2, Ebony Dashiell-Aje, PhD1, David A. Andrae, PhD1;
1BioMarin Pharmaceutical Inc., Novato, CA, USA, 2Clinical Outcomes Solutions, Tucson, AZ, USA
1BioMarin Pharmaceutical Inc., Novato, CA, USA, 2Clinical Outcomes Solutions, Tucson, AZ, USA
OBJECTIVES: Phenylketonuria (PKU) is a rare metabolic genetic disorder caused by deficiency of phenylalanine hydroxylase, leading to elevated phenylalanine (Phe) within the blood and brain, resulting in cognitive, psychological, and emotional symptoms that, even when treated early, often affect health-related quality of life (HRQOL). To support treatment development and disease management, the Phenylketonuria Symptom Severity and Impacts Scale (PKU-SSIS) was developed as a disease-specific patient-reported outcome measure to understand the symptom experience of individuals with PKU and impacts on everyday life. This study evaluated the psychometric properties of the PKU-SSIS Adolescent Version to determine its suitability for use in the adolescent PKU population.
METHODS: A non-interventional study of the PKU-SSIS (adolescents aged 12-17 years and their caregivers) was completed using an online survey at two timepoints. Participants were recruited across the United States and Canada through PKU summer camps, patient advocacy groups, healthcare professionals, and third-party recruiters. Participants also completed the Behavior Rating Inventory of Executive Function-Second Edition (BRIEF-2) screener, the Adolescent PKU-QOL, and global anchor items to assess psychometric properties of the PKU-SSIS.
RESULTS: Adolescents (n=57) with PKU completed surveys two weeks apart. Initial item level analyses supported a unidimensional graded response model after collapsing PKU-SSIS response options into a dichotomous scale. Internal consistency reliability was strong (KR-20 = 0.84), and test-retest reliability was strong (ICC(2,1)=0.89 - 0.90). The PKU-SSIS total score demonstrated convergent validity between PKU-SSIS and BRIEF-2 (r=0.71) and between the PKU-SSIS and PKU-QOL items (Moodiness r=0.71; Sadness r=0.72; Anxiety r=0.62; Headache r=0.47; Tiredness r=0.66; Lack of concentration r=0.65; Slow thinking r=0.66; and Irritability r=0.47).
CONCLUSIONS: Findings demonstrate strong psychometric support for the PKU-SSIS total score including reliability and convergent validity of PKU-SSIS in adolescents. The PKU-SSIS is suitable for use in adolescents with PKU for assessing symptoms and further characterizing the impact of PKU in clinical research and practice.
METHODS: A non-interventional study of the PKU-SSIS (adolescents aged 12-17 years and their caregivers) was completed using an online survey at two timepoints. Participants were recruited across the United States and Canada through PKU summer camps, patient advocacy groups, healthcare professionals, and third-party recruiters. Participants also completed the Behavior Rating Inventory of Executive Function-Second Edition (BRIEF-2) screener, the Adolescent PKU-QOL, and global anchor items to assess psychometric properties of the PKU-SSIS.
RESULTS: Adolescents (n=57) with PKU completed surveys two weeks apart. Initial item level analyses supported a unidimensional graded response model after collapsing PKU-SSIS response options into a dichotomous scale. Internal consistency reliability was strong (KR-20 = 0.84), and test-retest reliability was strong (ICC(2,1)=0.89 - 0.90). The PKU-SSIS total score demonstrated convergent validity between PKU-SSIS and BRIEF-2 (r=0.71) and between the PKU-SSIS and PKU-QOL items (Moodiness r=0.71; Sadness r=0.72; Anxiety r=0.62; Headache r=0.47; Tiredness r=0.66; Lack of concentration r=0.65; Slow thinking r=0.66; and Irritability r=0.47).
CONCLUSIONS: Findings demonstrate strong psychometric support for the PKU-SSIS total score including reliability and convergent validity of PKU-SSIS in adolescents. The PKU-SSIS is suitable for use in adolescents with PKU for assessing symptoms and further characterizing the impact of PKU in clinical research and practice.
Conference/Value in Health Info
2026-05, ISPOR 2026, Philadelphia, PA, USA
Value in Health, Volume 29, Issue S6
Code
PCR142
Topic
Patient-Centered Research
Topic Subcategory
Patient-reported Outcomes & Quality of Life Outcomes
Disease
No Additional Disease & Conditions/Specialized Treatment Areas, SDC: Rare & Orphan Diseases