Employing an entropy-based measure of sway to probe postural stability in Fragile X Premutation carriers*

Carriers of the fragile X premutation are at risk of developing the late-onset neurodegenerative movement disorder Fragile X associated tremor/ataxia Syndrome. (FXTAS). Although only recently discovered, emerging research has revealed that premutation carriers exhibit various subtle deficits in certain aspects of cognition and stability well before the typical age of onset of FXTAS. This study aimed to characterize the premutation phenotype in terms of cognition and postural stability as well as investigating the relationship between these two faculties with the aim of identifying preclinical symptoms of FXTAS. Methods: A group of 12 female premutation carriers and 15 healthy controls had postural stability recorded while standing with their eyes open, closed, as well as during working memory and attention based dual-tasks. Postural sway was characterized through traditional parameters (area, path length, and velocity) as well as through entropy-based measures such as the Complexity Index. Results: There were no differences observed in terms of traditional parameters between groups. The control group exhibited higher complexity indices than carrier in both dual-task conditions. Similarly, the complexity index of the control group was significantly higher during both dual-tasks, compared to the baseline eyes open condition, while premutation carriers remained consistent across tasks. This may reflect a reduction in adaptive capacity in premutation carriers. Conclusion: A combination of traditional and entropy-based measures of sway may serve as an objective measure of dual-task interference in premutation carrier and reveal subtle changes in stability and postural control when under increased cognitive load.