Objective: To investigate changes in cortical activity of fragile X premutation carriers during self-paced sway to the limit of stability.

Background: The fragile X premutation is a genetic condition that leaves carriers of this premutation at risk of developing the neurodegenerative movement disorder Fragile X associated Tremor/Ataxia Syndrome (FXTAS). Recently, subtle motor deficits, including reduced limits of stability and slower postural corrections following perturbations, have been observed in carriers well before to the typical age of onset [1] Characterising motor issues and the corresponding neural networks involved in such processes may help identify individuals at higher risk of developing FXTAS.

Method: Postural control in 10 carriers (42.8± 3.4 years) and 10 controls (43.1 ±9.9) was assessed during a dynamic sway task, while high-density EEG was simultaneously recorded to assess cortical activation. Subjects started from a neutral stance and swayed to the limit of their stability in the anterior direction before returning to a neutral stance. Changes in EEG spectral power were analysed throughout the sway cycle.

Results: There was no significant difference between groups in terms of the distance travelled to the limit of stability (p=0.86) or the time to complete the sway cycle (p=0.12). Carriers took longer to reach their limit of stability (2.2s ± 0.68) compared to controls (1.71s ± 0.3) however, this did not reach the level of significance (p=0.054). There was no difference in cortical activity between groups in frontal, central or parietal regions as sway initiated or when the limit of stability was reached. The control group exhibited an increase in parietal beta activity at the limit of stability and when sway was initiated compared to the neutral stance (p=0.03, for both). Carriers did not exhibit such a change in beta power.

Conclusion: The results may suggest young premutation carriers exhibit subtle dynamic postural control deficits relative to healthy controls, while also exhibiting reduced cortical activation of parietal regions. The increase in parietal beta activity of controls may reflect processing of sensory information such as vestibular or proprioceptive information during the dynamic sway cycle, compared to resting stance. Carriers did not exhibit a change in beta power, possibly underlying the change in neural mechanisms governing postural control.

References: O’Keefe JA, Robertson-Dick E, Dunn EJ, Li Y, Deng Y, Fiutko AN, Berry-Kravis E, Hall DA. (2015) Characterization and Early Detection of Balance Deficits in Fragile X Premutation Carriers With and Without Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS). Cerebellum. 2015 Dec;14(6):650-62. doi: 10.1007/s12311-015-0659-7.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cortical-activation-during-dynamic-sway-of-young-fragile-x-premutation-carriers/