BACKGROUND: Familial chylomicronemia syndrome (FCS) is a rare metabolic disorder that impacts physical, emotional, social, and cognitive functioning. The FCS-Symptom and Impact Scale (FCS-SIS) patient-reported outcome (PRO) measure assesses common symptoms and impacts of FCS. This study was conducted to evaluate cross-sectional psychometric properties of the FCS-SIS and its scoring method.
METHODS: This multisite, cross-sectional, observational study of individuals with FCS was conducted in the United States and Canada. Participants completed a survey composed of 7 PRO measures, including the FCS-SIS, and questions about clinical characteristics and demographics. The structure of the FCS-SIS was evaluated using inter-item and item-scale correlations and internal consistency reliability. Construct, known-groups, and criterion validity were evaluated by examining associations between FCS-SIS item and composite scores and other measures included within the survey.
RESULTS: Most of the 33 participants were female (63.6%) and White (78.1%). On average, participants reported first noticing FCS symptoms at ~16 years, with abdominal pain the most frequently reported initial symptom (n=20). Participants reported 2.5 acute pancreatitis attacks on average over the past year. Average FCS-SIS symptom item scores ranged from 1.8 to 3.9 (on a 0-to-10 scale [none-to-worst-possible]) within the 24-hour recall period, with an average Symptom composite score of 2.7. The average impact item scores on the FCS-SIS ranged from 1.6 to 3.0 (on a 0-to-4 scale), with an average Impact composite score of 2.1. Inter-item correlations between the FCS-SIS Symptom items ranged from 0.32 to 0.78. Corrected item-total correlations were highly satisfactory for Impact items, ranging from 0.62 to 0.85. All a priori validity hypotheses were supported by observed correlations and score differences between known groups.
CONCLUSION: The results of this study support the structure, reliability, and validity of the FCS-SIS, laying the psychometric groundwork for longitudinal evaluation of its utility in assessing treatment benefit in FCS clinical studies.
