Development and preliminary evidence of the psychometric properties of the GNE myopathy functional activity scale.

Abstract

GNE myopathy, a rare, severe, progressive myopathy, presents with lower extremity distal muscle weakness. The GNE myopathy functional activity scale (GNEM-FAS) evaluates the impact of GNE myopathy on functioning in adults. This paper presents the psychometric validation of the GNEM-FAS. Validation of the GNEM-FAS was performed using data from a randomized, double-blind, placebo-controlled Phase-II study (n = 46). Domain score distributions were acceptable. Moderate inter-item correlations (typical range, 0.40-0.70), strong item convergent and discriminant validity and high internal consistency reliability (α = 0.88-0.92) supported the instrument structure. Test-retest reliability was strong (ICC range: 0.87-0.95). Scale scores distinguished among subjects with differing disease severity (p < 0.05). This study provides preliminary evidence of the GNEM-FAS as a valid, reliable assessment.