Background: Aicardi-Goutières syndrome (AGS) is a rare genetic disorder characterized by a spectrum of motor abilities. While the Aicardi-Goutières syndrome severity score favors severely impacted individuals, there is an unmet need to define tools measuring function across the Aicardi-Goutières syndrome spectrum as potential outcome assessments for future clinical trials. Methods: Gross Motor Function Measure-88 (GMFM-88) and AGS Severity Scale were administered in individuals affected by Aicardi-Goutières syndrome (n = 71). We characterized the performance variability by genotype. Derived versions of the GMFM-88, including the GMFM-66, GMFM-66 item set (GMFM-66IS), and GMFM-66 Basal&Ceiling (GMFM-66BC) were calculated. The Aicardi-Goutières syndrome cohort was divided into severe (AGS Severity Scale score <4) or attenuated (≥4). Performance on the AGS Severity Scale highly correlated with total GMFM-88 scores (Spearman Correlation: R = 0.91). To assess variability of the GMFM-88 within genotypic subcohorts, interquartile ranges (IQRs) were compared. Results: GMFM-88 performance in the TREX1 cohort had least variability while the SAMHD1 cohort had the largest IQR (4.23 vs 81.8). Floor effect was prominent, with most evaluations scoring below 20% (n = 46, 64.79%), particularly in TREX1- and RNASEH2-cohorts. Performance by the GMFM-66, GMFM-66IS, and GMFM-66BC highly correlated with the full GMFM-88. The Aicardi-Goutières syndrome population represents a broad range of gross motor skills. Conclusions: This work identified the GMFM-88 as a potential clinical outcome assessment in subsets of the Aicardi-Goutières syndrome population but underscores the need for additional validation of outcome measures reflective of the diverse gross motor function observed in this population, including low motor function. When time is limited by resources or patient endurance, shorter versions of the GMFM-88 may be a reasonable alternative.
Keywords: Aicardi-Goutières syndrome; GMFM-88; gross motor function; outcome measures.